Showing papers in "Ibis in 2015"
TL;DR: The authors tracked 19 juvenile Egyptian Vultures from the declining breeding population on the Balkan Peninsula between 2010 and 2014 to estimate survival and identify important migratory routes and wintering areas for this species.
Abstract: Many populations of long-distance migrants are declining and there is increasing evidence that declines may be caused by factors operating outside the breeding season. Among the four vulture species breeding in the western Palaearctic, the species showing the steepest population decline, the Egyptian Vulture Neophron percnopterus, is a longdistance migrant wintering in Africa. However, the flyways and wintering areas of the species are only known for some populations, and without knowledge of where mortality occurs, effective conservation management is not possible. We tracked 19 juvenile Egyptian Vultures from the declining breeding population on the Balkan Peninsula between 2010 and 2014 to estimate survival and identify important migratory routes and wintering areas for this species. Mortality during the first autumn migration was high (monthly survival probability 0.75) but mortality during migration was exclusively associated with suboptimal navigation. All birds from western breeding areas and three birds from central and eastern breeding areas attempted to fly south over the Mediterranean Sea, but only one in 10 birds survived this route, probably due to stronger tailwind. All eight birds using the migratory route via Turkey and the Middle East successfully completed their first autumn migration. Of 14 individual and environmental variables examined to explain why juvenile birds did or did not successfully complete their first migration, the natal origin of the bird was the most influential. We speculate that in a declining population with fewer experienced adults, an increasing proportion of juvenile birds are forced to migrate without conspecific guidance, leading to high mortality as a consequence of following sub-optimal migratory routes. Juvenile Egyptian Vultures wintered across a vast range of the Sahel and eastern Africa, and had large movement ranges with core use areas at intermediate elevations in savannah, cropland or desert. Two birds were shot in Africa, where several significant threats exist for vultures at continental scales. Given the broad distribution of the birds and threats, effective conservation in Africa will be challenging and will require long-term investment. We recommend that in the short term, more efficient conservation could target narrow migration corridors in southern Turkey and the Middle East, and known congregation sites in African wintering areas.
90 citations
TL;DR: Hybridization, the interbreeding of different species, plays an important role in several evolutionary processes, such as adaptive trait transfer, adaptive radiations, and the origin of new species.
Abstract: Hybridization, the interbreeding of different species, plays an important role in several evolutionary processes, such as adaptive trait transfer (Arnold 2006, Arnold et al. 2008, Hedrick 2013), adaptive radiations (Seehausen 2004), and the origin of new species (Mavarez & Linares 2008, Abbott et al. 2013, Schumer et al. 2014). However, hybridization can have detrimental effects for the species involved: one of the species can be driven to extinction (Rhymer & Simberloff 1996) or two species can merge into one leading to a loss in biodiversity (Seehausen 2006, Seehausen et al. 2008), so hybridization has also become a relevant topic in conservation (Allendorf et al. 2001, Brumfield 2010).
77 citations
TL;DR: It is concluded that while corvids can have a negative impact on bird species, their impact is small overall, and nearly five times more frequent for productivity than for abundance.
Abstract: Corvids are often viewed as efficient predators capable of limiting prey species populations. Despite this widely held belief, a comprehensive review quantifying the effect of corvids on the demography of prey species is lacking. We examine the impacts of crows, ravens Corvus spp. and Eurasian Magpies Pica pica on the population parameters of other bird species. We summarize results from 42 studies, which included 326 explicit evaluations of relationships between a corvid and a potential prey species. Population parameters of studied prey species were categorized as abundance-related (numbers, nest density) or productivity-related (nest success, brood size). Information from both experimental removal studies and correlative studies was examined. Combining all studies, no negative influence of corvids on either abundance or productivity of prey species was found in 81% of cases. Negative impacts were significantly more likely in cases examining productivity rather than abundance (46 vs. 10%). Experimental studies that removed only corvid species were significantly less likely to show a positive impact on productivity than those removing corvids alongside other predators (16 vs. 60%). This suggests that the impact of corvids is smaller than that of other predators, or that compensatory predation occurs. The impact of corvids was similar between diverse avian groups (such as gamebirds, passerines and waders; or ground-nesting and other species). Crows were found to be significantly more likely to have a negative impact on prey species productivity than were Magpies (62 vs. 12%), but no differences were found in relation to prey abundance. We conclude that while corvids can have a negative impact on bird species, their impact is small overall, and nearly five times more frequent for productivity than for abundance. These results suggest that in most cases bird populations are unlikely to be limited by corvid predation and that conservation measures may generally be better targeted at other limiting factors. However, negative impacts were found in a minority of cases, and those may require further investigation to develop management tools to mitigate such impacts where they are of economic or conservation concern.
74 citations
TL;DR: This work was supported by the Lanier Honour Scholarship, part of the Cornelius Vanderbilt Program at Vanderbilt Uinversity, and partially provided by the Regional Government of Balearic Islands and FEDER funding.
Abstract: Funds were partially provided by the Regional Government of Balearic Islands and FEDER funding. E.C.S. was supported by the Lanier Honour Scholarship, part of the Cornelius Vanderbilt Program at Vanderbilt Uinversity
61 citations
TL;DR: It is shown that nest survival was higher on herb-rich meadows than on monocultures, and similar to the 1980s, so it seems that increased predator densities are an increased threat during the egg stage only if habitat quality is low and high-quality habitat in the form of herb- rich meadows provides a degree of protection against predators.
Abstract: Effective conservation of endangered species requires a solid understanding of the demographic causes of population change. Bird populations breeding on agricultural grasslands have declined because their preferred habitat of herb-rich meadows has been replaced by grassland monocultures. The timing of agricultural activities in these monocultural grasslands is critical, as they often coincide with the nesting phase of breeding birds. Here, we aim to identify the effect of habitat management and targeted nest protection on nest survival of Black-tailed Godwits Limosa limosa in the Netherlands, a population that has shown a 70% reduction in breeding population size since the 1970s. To protect nests in monocultures from destruction, farmers are paid to either delay mowing or leave a patch of unmown grass around the nest, a patch which in practice varied in size. In herb-rich meadows, which are typically managed for bird conservation purposes, mowing occurs after hatching. Nest survival declined as the season advanced, more steeply on monocultures than on meadows. Targeted nest protection was only partially successful, as nest predation was considerably higher on mown grassland monocultures with small unmown patches around the nest than in mown monocultures with large unmown patches and in unmown fields. Increased predator densities over the years have been suggested as an important cause of the trend towards lower nest survival, but here we show that nest survival was higher on herb-rich meadows than on monocultures, and similar to the 1980s. It thus seems that increased predator densities are an increased threat during the egg stage only if habitat quality is low. High-quality habitat in the form of herb-rich meadows therefore provides a degree of protection against predators.
54 citations
TL;DR: Books on population densities and abundance changes across habitats in one of the world's largest and most threatened bird families, the parrots, are reviewed to identify gaps in knowledge, model phylogenetic and other influences on abundance, and seek patterns that might guide thinking for data-deficient taxa and situations.
Abstract: Estimates of population density and abundance change (differences in density or encounter rates across land uses or time periods) form the cornerstone of much of our knowledge of species' responses to environmental conditions, extinction risks and potential conservation actions. Gathering baseline data on abundance of the world's c. 10 000 bird species and monitoring trends in the light of rapidly changing environmental and harvest pressures is a daunting prospect. With this in mind, we review literature on population densities and abundance changes across habitats in one of the world's largest and most threatened bird families, the parrots (Psittaciformes), to identify gaps in knowledge, model phylogenetic and other influences on abundance, and seek patterns that might guide thinking for data-deficient taxa and situations. Density estimates were found for only 25% of 356 parrot species. Abundance change data were similarly limited and most came from logged forest, with very few comparisons across different anthropogenic habitats. Threatened species were no more likely to have a density estimate than non-threatened species, and were less likely to have estimates of abundance change. Exploratory generalized linear mixed models indicated that densities are most influenced by genus, and are generally higher within protected areas than outside. It is unclear whether the latter effect stems from habitat protection, a reduction in poaching or both, but protected areas appear to be beneficial for parrots. Individual members of the ‘parakeet’ genera (e.g. Pyrrhura and Eos) were predictably abundant, whereas within larger-bodied genera such as Ara (macaws), species were predictably uncommon (< 10 individuals per km2) and there was a long tail of extreme rarity. Responses of parrots to habitat change were highly variable, with natural variation in parrot abundance across different primary forests as great as that between primary forest and human-altered forests. The speed at which environmental change is affecting the world's parrots far outstrips that of our current capacity to track their abundance and we assess the likely scale of data deficiency in this and other bird groups. Developments in survey and analysis methods such as variants of distance sampling and the integration of niche modelling with point density estimation may increase our effectiveness in monitoring parrots and other important and threatened bird groups.
44 citations
TL;DR: Daily, monthly and seasonal patterns in fluxes at rotor heights and the influence of wind direction on flight intensity are demonstrated, among the first to show the magnitude and variation of low-altitude flight activity across the North Sea.
Abstract: Assessing the impacts of avian collisions with wind turbines requires reliable estimates of avian flight intensities and altitudes, to enable accurate estimation of collision rates, avoidance rates and related effects on populations. At sea, obtaining such estimates visually is limited not only by weather conditions but, more importantly, because a high proportion of birds fly at night and at heights above the range of visual observation. We used vertical radar with automated bird-tracking software to overcome these limitations and obtain data on the magnitude, timing and altitude of local bird movements and seasonal migration measured continuously at a Dutch offshore wind farm. An estimated 1.6 million radar echoes representing individual birds or flocks were recorded crossing the wind farm annually at altitudes between 25 and 115 m (the rotor-swept zone). The majority of these fluxes consisted of gull species during the day and migrating passerines at night. We demonstrate daily, monthly and seasonal patterns in fluxes at rotor heights and the influence of wind direction on flight intensity. These data are among the first to show the magnitude and variation of low-altitude flight activity across the North Sea, and are valuable for assessing the consequences of developments such as offshore wind farms for birds.
41 citations
TL;DR: It is shown that the individual quality of the breeder and the timing of their first clutches are key factors influencing the decision to double brood, and thereby that they are important determinants of reproductive performance in Eurasian Hoopoes.
Abstract: Double brooding may be a good strategy for short-lived species to maximize annual and lifetime reproductive success (ARS and LRS, respectively). Nevertheless, there is typically individual variation in the probability of producing a second clutch. Here we evaluate factors that influence the decision to double brood in the Eurasian Hoopoe Upupa epops. Analyses of an 11-year dataset showed that 36% of the females and 21% of the males produced a second clutch after successfully raising a first clutch. Double-brooded females had higher ARS (9.1 ± 1.9 fledglings; mean ± se) and LRS (0.93 ± 0.08 recruits) than single-brooded females (ARS: 4.5 ± 2.1 fledglings; LRS: 0.36 ± 0.03 recruits). This suggests that double brooding is adaptive in Hoopoes, and raises the question of why most individuals only produce one clutch per season. The probability of double brooding varied only slightly between years, suggesting that it is influenced by individual characteristics rather than by external, population-level environmental factors. In both sexes, the probability of double brooding increased with earlier timing of the first clutch, and the timing of reproduction was the most important factor influencing reproductive success. The latter is likely to be mediated by changes in resources during the season. The probability of double brooding also increased slightly with female age, due to differences in intrinsic quality among females rather than to a gain in experience. In contrast to many other studies, the probability of double brooding increased with an increasing number of fledglings from the first clutch, suggesting that it is a strategy of individuals of high quality. Taken together, we show that the individual quality of the breeder and the timing of their first clutches are key factors influencing the decision to double brood, and thereby that they are important determinants of reproductive performance in Eurasian Hoopoes.
39 citations
TL;DR: This work finds that corticosterone from feathers (CORTf) is negatively related to trophic position (TP) inferred from feather stable-nitrogen isotope values (d 15 N) in Leach’s Storm-petrels Oceanodroma leucorhoa, and shows the first evidence of a correlation between individual endocrine levels and foraging ecology.
Abstract: Diet during the non-breeding period influences condition and subsequent reproduction. Physiological mechanisms underlying such carry-over effects are poorly understood but could be clarified by studying physiological responses to variation in diet during nonbreeding. The hormone corticosterone provides a functional link between diet and survival and reproduction, but methodological limitations have prevented previous studies from testing the hypothesis that, on an individual level, avian corticosterone levels during the non-breeding period reflect broader patterns in feeding ecology during that time. Using museum specimens (1859–2002) and live birds (2012), we found that corticosterone from feathers (CORTf) is negatively related to trophic position (TP) inferred from feather stable-nitrogen isotope values (d 15 N) in Leach’s Storm-petrels Oceanodroma leucorhoa. CORTf was not related to stable-carbon isotope values (d 13 C). We detected no temporal trends in CORTf or d 15 N, and neither was related to a large-scale index of winter climate, suggesting a general ecological phenomenon rather than a reflection of historical environmental changes. However, we detected a temporal trend in feather d 13 C, and d 13 C was related to d 15 N. Our findings suggest a physiological benefit of feeding at higher TPs, either through increased nutritional value or reduced foraging costs associated with higher TP prey, and future research should aim to distinguish between these two explanations. Nevertheless, ours is the first evidence of a correlation between individual endocrine levels and foraging ecology, and demonstrates non-lethal variation in a physiological mediator in turn related to variation in resource use.
38 citations
TL;DR: It is considered that all populations of Rufous-thighed Kites are fully migratory, wintering in Equatorial forests in the Amazonian basin, and this discovery requires a reassessment of the species’ global conservation status as an Atlantic Forest breeding endemic, threatened by habitat loss and degradation.
Abstract: Gaps in our knowledge of the geographical distribution of species represent a fundamental challenge to biogeographers and conservation biologists alike, and are particularly pervasive in the tropics. Here we highlight the case of the Rufous-thighed Kite Harpagus diodon, a South American raptor commonly mapped as resident across half the continent. Recent observations at migration watch points have indicated it may be partially migratory in the southernmost parts of its range. To investigate this possibility, we collated contemporary and historical specimen records, published sight records and ‘digital vouchers’ – photographs and sound-recordings archived online (from citizen science initiatives) – and explored the spatiotemporal distribution of records. We were unable to trace any documented records of this species from Amazonia during the austral summer (October–March), or records from the Atlantic Forest biome during the peak of the Austral winter (June–August), and all proven breeding records stem from the Atlantic Forest region. We compared this pattern with that of a ‘control’ species, the congeneric Double-toothed Kite H. bidentatus, again using specimens and digital vouchers. For this species we found no evidence of seasonality between biomes and can disregard spatiotemporal variation in observer effort as a cause of seasonal biases. We consider that all populations of Rufous-thighed Kites are fully migratory, wintering in Equatorial forests in the Amazonian basin. We provide evidence that this pattern was previously obscured by erroneous undocumented records and poor or erroneous specimen metadata, and its discovery was primarily facilitated by digital vouchers. This discovery requires a reassessment of the species’ global conservation status as an Atlantic Forest breeding endemic, threatened by habitat loss and degradation, as it was previously considered to be resident across large swathes of undisturbed Amazonian Forest on the Guiana Shield. The bulk of the digital voucher data used to elucidate this pattern were extracted from a Brazilian citizen science initiative WikiAves, which may serve as a model for collating biodiversity data in megadiverse countries and help catalyse environmental awareness.
36 citations
TL;DR: It is suggested that the decision made by thousands of householders to provide supplementary food for Red Kites in their gardens is the primary factor explaining their daytime abundance in this urban area.
Abstract: Reintroductions are commonly used to mitigate biodiversity loss. One prominent example is that of the Red Kite Milvus milvus, a charismatic raptor of conservation concern. This species has been reintroduced across the UK over the last 25 years following its near extinction after centuries of persecution. The species was not expected to recolonize urban areas; its historical association with human settlements is attributed to scavenging on human waste and refuse, a resource now greatly reduced on the streets of modern European cities. However, the species has become a common daytime visitor to a large conurbation centred on the town of Reading, southern England, approximately 20 km from the first English reintroduction site. Given a near-absence of breeding and roost sites, we investigated foraging opportunities and habitat associations that might explain use by Red Kites of this urban area. Surveys of discarded human foods and road-kill suggested that these could support at most 13–29 Kites per day. Face-to-face surveys of a cross-section of residents revealed that 4.5% (equivalent to 4349 households) provided supplementary food for Red Kites in their gardens. Using estimates of per-household resource provision from another study, we calculated that this is potentially sufficient to feed 142–320 Kites, a substantial proportion of the total estimated to visit the conurbation each day (between 140 and 440). Road transects found positive associations between Red Kites and residential areas. We suggest that the decision made by thousands of householders to provide supplementary food for Red Kites in their gardens is the primary factor explaining their daytime abundance in this urban area.
TL;DR: This paper used an automated radiotelemetry array extending 350km from southwest Nova Scotia to southern Maine to study the migratory and stopover movements of Northern Waterthrushes Parkesia noveboracensis, Red-eyed Vireos Vireo olivaceus and Yellow-rumped Warblers Setophaga coronata in relation to fuel load and weather at the northeastern edge of the Gulf of Maine.
Abstract: Departure decisions of songbirds at ecological barriers they encounter en route can strongly influence time, energy and survival costs of migration. To date, most field studies of departure decisions and their correlates have used indirect methods and followed migrants at a single stopover site, with limited information on what happens to individuals after they depart from the site. We used an automated radiotelemetry array extending 350km from southwest Nova Scotia to southern Maine to study the migratory and stopover movements of Northern Waterthrushes Parkesia noveboracensis, Red-eyed Vireos Vireo olivaceus and Yellow-rumped Warblers Setophaga coronata in relation to fuel load and weather at the northeastern edge of the Gulf of Maine. From the 105 radio-transmitters we deployed in southwest Nova Scotia, we recorded 42 landscape-scale stopover flights and 47 migratory flights by 75 individuals. Of the migratory flights, 57% were orientated southwest, a trajectory that, if held, would require individuals to complete a 350-440km overwater flight. The remaining 43% of migratory flights were orientated northwest, away from the Gulf of Maine, and 15 individuals were confirmed to have detoured around all or a portion of the barrier, as evidenced by their being re-detected over the Bay of Fundy and/or along the coast of Maine between 4h and 15days later. Across all individuals, initial fat score had a positive effect on departure probability, especially for individuals that made stopover flights. Among weather variables, tailwind assistance was the best predictor of migratory departures but did not appear to be the main factor determining whether individuals orientated towards or away from the Gulf of Maine. Weather had little effect on departure decisions of individuals that made stopover flights. These differences in the correlates of migratory departures and stopover flights would probably not have been distinguishable had our study been restricted to a local scale. Therefore, our findings highlight the importance of expanding the scale at which departure decisions and the ecology of stopover in general are studied.
TL;DR: In this article, the authors assessed whether daily water flux (DWF) is higher on hot days, reflecting increases in evaporative cooling demands, in an arid-zone bird that obtains its water through food intake.
Abstract: Endothermic animals resident in hot, arid terrestrial environments are likely to face a trade-off between their ability to obtain water and elevated thermoregulatory water requirements. We assessed whether daily water flux (DWF) is higher on hot days, reflecting increases in evaporative cooling demands, in an arid-zone bird that obtains its water through food intake. We obtained measurements of DWF (partitioned into water influx and efflux rates) in 71 White-browed Sparrow-Weavers Plocepasser mahali at a desert site and a semi-desert site, during summer in the Kalahari Desert of southern Africa. We found no evidence that DWF varied with maximum daily air temperature (Tair, range = 27.6–39.2 °C). Instead, DWF was lower during dry periods than in the wet season at the semi-desert site. Furthermore, birds showed deficits in water balance (water influx/water efflux) during the dry periods at both sites. Our data show that DWF is low in a non-drinking bird that obtains its water through food, and that demands for evaporative water loss on very hot days (maximum Tair of 40–44 °C) may exceed water intake rates during hot and dry periods. Species that do not have opportunities to drink will experience strong trade-offs between thermoregulation, hydration state and activity levels as temperatures increase.
TL;DR: It is argued that songs evolved to be more complex in species-poor, demonstrably less noisy environments, and this has led to the great diversity in song that has been documented among five Phylloscopus species.
Abstract: Aspects of birdsong complexity, such as the number of distinct notes in a song, commonly increase along latitudinal gradients, a pattern for which at least 10 explanations have been suggested In two Himalayan warblers, songs are more complex in the northwest than in the southeast In Grey-hooded Warbler Phylloscopus xanthoschistos, high complexity results from increased note diversity within song types, sung across a higher bandwidth In Blyth's Leaf Warbler Phylloscopus reguloides, high complexity is a consequence of increased variation between song types The hypothesis with strongest support is that songs evolved to be more complex in species-poor, demonstrably less noisy environments We consider geographical variation to be an outcome of sexual selection favouring complexity across environments, where detection of the signal varies Sexual selection favouring complexity may be resolved in different ways, because complexity has multiple features (repertoire size, song switching, etc) We argue this has led to the great diversity in song that we have documented among five Phylloscopus species
TL;DR: No support for a link between wing length and migration is found, indicating that wingshape is a more important predictor of shorebird migratory behaviour than wing length, and the results suggest that total migration distance and migratory strategy may act on the evolution of wing shape in shorebirds, and possibly in other avianspecies.
Abstract: Migration is an energetically expensive and hazardous stage of the annual cycle of non-resident avian species, and requires certain morphological adaptations. Wing shape is oneof the morphological traits that is expected to be evolutionarily shaped by migration.Aerodynamic theory predicts that long-distance migrants should have more pointedwings with distal primaries relatively longer than proximal primaries, an arrangementthat minimizes induced drag and wing inertia, but this prediction has mostly been testedin passerine species. We applied the comparative method of phylogenetically indepen-dent contrasts to assess convergent evolution between wing shape and migration withinshorebirds. We confirmed the assumption that long-distance migrants have less roundedwings than species migrating shorter distances. Furthermore, wing roundedness nega-tively correlates with fat load and mean distance of migratory flights, the basic compo-nents of migration strategies. After controlling for interspecific differences in body size,we found no support for a link between wing length and migration, indicating that wingshape is a more important predictor of shorebird migratory behaviour than wing length.The results suggest that total migration distance and migratory strategy may simulta-neously act on the evolution of wing shape in shorebirds, and possibly in other avianspecies.Keywords: comparative method, convergent evolution, ecomorphology, migration, wing shape.There is growing evidence that avian wing shapehas evolved in response to changes in migratorybehaviour (M€onkk €onen 1995, Lockwood et al.1998). This hypothesis is based on the classicalprediction of aerodynamic theory, which assumesthat long-distance migratory species should havemore pointed wings (Videler 2006). Pointed wingshave distal primaries that are relatively longer thanproximal primaries, locating the wing tip close tothe leading edge of the wing. Such a wing shape isconsidered to be more efficient during long-distance migration, as it sheds weaker vortices andgenerates little lift at the tips, helping to minimizeinduced drag (Swaddle & Lockwood 2003).Pointed wingtips are also suggested to minimizewing inertia and weight (Rayner 1988, Lockwoodet al. 1998). High wing pointedness reduces heartrate and the rate of energy expenditure duringflight in migrating passerines (Bowlin & Wikelski2008). In contrast, rounded wings generate greaterinduced drag associated with larger vortices at thetips, aiding take-off speed and manoeuvrability,but sub-optimal for migration (Lockwood et al.1998).The hypothesis of convergent evolution of wingmorphology and migration strategy has most fre-quently been tested within species by comparingwing shape between populations or subspeciesshowing different migratory habits. Although mostof these comparisons have confirmed assumptionsof the correlated evolution of wing pointedness
TL;DR: The Alpine Rock Ptarmigan Lagopus muta helvetica is considered to be particularly vulnerable to climate change because it lives exclusively above the treeline in alpine habitats and is adapted to cold climates as mentioned in this paper.
Abstract: The Alpine Rock Ptarmigan Lagopus muta helvetica is considered to be particularly vulnerable to climate change because it lives exclusively above the treeline in alpine habitats and is adapted to cold climates. Its Swiss population index has decreased over the last two decades. A considerable shrinkage in distributional area is predicted with further climate change. We assess whether the Alpine Rock Ptarmigan has moved to higher elevations in recent years in the Swiss Alps, and whether such elevational shifts have differed between regions and seasons, using observations recorded by volunteers over a 29-year period. The elevational shifts differed greatly between regions. In the Eastern and Southern Alps, Ptarmigans were increasingly recorded at higher elevations, with a mean uphill shift of 6.4–9.4 m/year over the last three decades, a pattern that could not be explained by the yearly variation in weather conditions, whereas there was only a moderate upward shift (1.5–3.2 m/year) in the Northern Alps and almost no shift in the Western Alps. Elevational changes were generally greater than those observed in other bird species. The observed upward shift in the Eastern and Southern Alps is among the fastest observed in animals and plants, and may be caused by an upward shift of the treeline and reforestation of formerly cut or unforested areas. The observed elevational shift of the distribution of the Alpine Rock Ptarmigan has led to a reduction in the range of this subspecies, which is restricted to the Alps and isolated from other populations.
TL;DR: ‘Birdfields’, as a targeted AES for Montagu's Harriers, is more effective than previous AES due to increased prey accessibility, and it is advocated that AES should always include monitoring and research activities, aiming at a more adaptive conservation approach.
Abstract: Farmland birds are in steep decline and agri-environment schemes (AES) to counteract these biodiversity losses are expensive and inefficient. Here we test a novel AES, ‘Birdfields’, designed using detailed ecological knowledge of the target species, Montagu's Harrier Circus pygargus. Current AES, such as field margins, that aim to improve foraging conditions (i.e. vole densities) for harriers are inefficient, as prey are difficult to capture in tall set-aside habitat. ‘Birdfields’ combines strips of set-aside to boost vole numbers and strips of alfalfa, as voles are accessible after alfalfa has been harvested. We found that vole numbers were generally highest in set-aside. Montagu's Harriers fitted with GPS-loggers used ‘Birdfields’ intensively after mowing, preferring mown to unmown strips. Thus, prey availability appeared more important than prey abundance. Thus, ‘Birdfields’, as a targeted AES for Montagu's Harriers, is more effective than previous AES due to increased prey accessibility. An additional advantage of ‘Birdfields’ is that it is considerably cheaper, due to the harvest of alfalfa. We advocate that AES should always include monitoring and research activities, aiming at a more adaptive conservation approach.
TL;DR: This research presents a meta-anatomy of the natural history of the Amazon rainforest from 1989 to 2002, a period chosen in order to explore its roots as well as specific cases up to and including the year in which the Amazonian rainforest was devastated.
Abstract: Fil: Blendinger, Pedro Gerardo. Universidad Nacional de Tucuman. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Instituto de Ecologia Regional; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina
TL;DR: Within large plantation-forest landscapes, a variety of growth stages is important for this species and the results suggest that grazing of open habitats within and adjacent to forest will additionally benefit the European Nightjar.
Abstract: In Europe, the consequences of commercial plantation management for birds of conservation concern are poorly understood. The European Nightjar Caprimulgus europaeus is a species of conservation concern across Europe due to population depletion through habitat loss. Pine plantation-forest is now a key Nightjar nesting habitat, particularly in northwestern Europe, and increased understanding of foraging habitat selection is required. We radiotracked 31 Nightjars in an extensive (185-km2) complex conifer plantation landscape in 2009 and 2010. Home-range 95% kernels for females, paired males and unpaired males were an order of magnitude larger than song territories of paired males, emphasizing the importance of habitats beyond the song territory. Nightjars travelled a mean maximum distance of 747 m from the territory centre each night. Homerange placement relative to landscape composition was examined by compositional analysis. Pre-closure canopy forest (aged 5–10 years) was selected at all scales (MCP, 95% and 50% kernels), with newly planted forest (aged 0–4 years) also selected within 50% kernels. For telemetry fixes relative to habitat composition within 2 km of their territory centre, individuals again selected pre-closure and newly planted forest, and also grazed grass heath. Open ungrazed habitat was not selected, with implications for open habitat planning for biodiversity conservation within public-owned forests. Despite the Nightjars’ selection for younger growth, moth biomass was greater in older forest stands, suggesting that foraging site selection reflects ease of prey capture rather than prey abundance. Within large plantation-forest landscapes, a variety of growth stages is important for this species and our results suggest that grazing of open habitats within and adjacent to forest will additionally benefit the European Nightjar.
TL;DR: Test whether the availability of invertebrate prey limits the breeding success and adult abundance of House Sparrows in suburban London, where House Sparrow populations declined by 60% during the decade preceding this study.
Abstract: Factors affecting avian demography and abundance in urban landscapes are poorly understood and this hinders attempts to manage urban bird communities. Several recent studies indicate that lack of invertebrate prey in urban landscapes may constrain avian productivity and fitness relative to that in other habitats. House Sparrow Passer domesticus populations have undergone large declines in many European urban centres and inadequate reproductive success linked to invertebrate availability has been postulated as a potential cause of these declines. We conducted a replicated supplementary feeding experiment to test whether the availability of invertebrate prey limits the breeding success and adult abundance (colony size) of House Sparrows in suburban London, where House Sparrow populations declined by 60% during the decade preceding our study. Daily mealworm provision over two successive breeding seasons, sufficient to provide 82% of chick energy requirements of House Sparrow pairs nesting within 50 m of feeders, had a large positive impact on the abundance of recently fledged birds (+62%), but only a small positive impact, limited mainly to small colonies, on the overall abundance of territorial males. Colony growth was only weakly related to fledgling abundance in the previous year and did not appear to be constrained by nest-site availability. Conservation interventions that enhance invertebrate availability for suburban House Sparrows may increase reproductive success but are unlikely, on their own, to lead to population growth or recovery.
TL;DR: This work combined analyses of native and non-native realized climate niches to understand differences between models based on all locations, as well as on locations from the native range only, and showed that SDMs based on location data from native areas alone may underestimate the potential distribution of a given species.
Abstract: Non-native species can have severe impacts on ecosystems. Therefore, predictions of potentially suitable areas that are at risk of the establishment of non-native populations are desirable. In recent years, species distribution models (SDMs) have been widely applied for this purpose. However, the appropriate selection of species records, whether from the native area alone or also from the introduced range, is still a matter of debate. We combined analyses of native and non-native realized climate niches to understand differences between models based on all locations, as well as on locations from the native range only. Our approach was applied to four estrildid finch species that have been introduced to many regions around the world. Our results showed that SDMs based on location data from native areas alone may underestimate the potential distribution of a given species. The climatic niches of species in their native ranges differed from those of their non-native ranges. Niche comparisons resulted in low overlap values, indicating considerable niche shifts, at least in the realized niches of these species. All four species have high potential to spread over many tropical and subtropical areas. However, transferring these results to temperate areas has a high degree of uncertainty, and we urge caution when assessing the potential spread of tropical species that have been introduced to higher latitudes.
TL;DR: It is suggested that the distribution and activity of nest predators in lowland wet grassland landscapes may be influenced by the presence and distribution of areas of taller vegetation, and there may be scope for landscape-scale management of vegetation structure to influence levels of predation in these habitats.
Abstract: In Europe, lowland wet grasslands have become increasingly fragmented, and populations of waders in these fragments are subject to unsustainably high levels of nest predation. Patches of taller vegetation in these landscapes can support small mammals, which are the main source of prey for many predators. Providing such patches of habitat could potentially reduce levels of nest predation if predators preferentially target small mammals. However, predator attraction to patches of taller vegetation for foraging, shelter, perching and/or nesting could also result in local increases in predation rates, as a consequence of increased predator densities or spill-over foraging into the surrounding area. Here we assess the influence of taller vegetation on wader nest predation rates, and the feasibility of managing vegetation structure to alter predator impacts. Between 2005 and 2011, the nest distribution and hatching success of Northern Lapwings Vanellus vanellus, which nest in the open, and Common Redshanks Tringa totanus, which conceal their nests in vegetation, were measured on a 487-ha area of wet grassland in eastern England that is primarily managed for breeding waders. Predation rates of Lapwing nests increased significantly with distance from patches of taller vegetation, and decreased with increasing area of taller vegetation within 1 km of the nest, whereas neither variable influenced Redshank nest predation probability. These findings suggest that the distribution and activity of nest predators in lowland wet grassland landscapes may be influenced by the presence and distribution of areas of taller vegetation. For Lapwings at least, there may therefore be scope for landscape-scale management of vegetation structure to influence levels of predation in these habitats.
TL;DR: In this article, the authors report on an 11-year study of floater interference in a population of Spanish Imperial Eagles Aquila adalberti and analyze changes over the years in the productivity of 15 territories to test predictions of two hypotheses of density-dependent productivity in relation to the presence of floaters.
Abstract: We report on an 11–year study of floater interference in a population of Spanish Imperial Eagles Aquila adalberti. We analyzed changes over the years in the productivity of 15 territories to test predictions of two hypotheses of density-dependent productivity in relation to the presence of floaters (birds without territories). According to the ‘interference’ hypothesis, the frequency of intrusion by floaters increases with density, resulting in a decrease in productivity. Thus, in a high-density population a negative relationship between floater intrusions and productivity of the territory is expected. In contrast, under the ‘habitat heterogeneity’ hypothesis, as density increases a higher proportion of individuals is forced to occupy lower quality habitats. Support of this hypothesis requires that floaters detect differences in quality among territories and preferentially visit the better quality territories. Consequently, a positive relationship between floater intrusions and productivity is expected. Results showed that floaters tended to visit their natal area at the beginning of the breeding season. Among floater eagles, males made significantly more intrusions per day than did females, but females stayed in the natal population for longer each year than males. Floater intrusions and productivity were highly positively correlated, supporting the ‘habitat heterogeneity’ hypothesis; individuals were apparently able to assess the quality of a territory and, at the frequencies observed, their interference with the breeding pair had no obvious negative effect on productivity.
TL;DR: In this paper, the authors present a simple and simple approach to study the relationship between wind conditions and departure likelihood of migrants at stopover sites, and show that the intensity of nocturnal migratory restlessness increases with increasing wind support towards the migratory goal.
Abstract: A variety of methods have been used to study the relationship between wind conditions and departure decisions of migrant birds at stopover sites. These methods are either costly or suffer from inaccuracy in determining whether or not an individual has resumed migration. Here we present a novel and simple approach to studying the relationship between wind conditions and departure likelihood. Northern Wheatears Oenanthe oenanthe caught during stopover were temporarily caged to measure their nocturnal migratory restlessness, which is an accurate proxy for their individual departure likelihood. We then related the degree of nocturnal restlessness to wind conditions prevailing at the time of capture. Confirming the general pattern from previous studies of departure, the intensity of nocturnal migratory restlessness, and hence departure likelihood, increased with increasing wind support towards the migratory goal. This suggests that approximating the propensity to depart by measuring nocturnal migratory restlessness is a reliable way to study the effect that wind conditions experienced during stopover has on the departure decision of migrants. Our study also shows that nocturnal migrants possess the ability to use information gathered during the day for their departure decisions at night. Because measuring migratory restlessness is straightforward and inexpensive, our approach is ideally suited to test hypotheses regarding spatio-temporal variation in wind selectivity in migrating birds.
TL;DR: The foraging habitat preferences of Scopoli's Shearwater Calonectris diomedea in the Mediterranean Sea are quantified to improve understanding of the at-sea distribution and habitat preference of a seabird inhabiting the over-exploited Mediterranean Sea.
Abstract: The distribution of seabirds at sea is influenced by physical, ecological and anthropogenic factors such as sea depth, prey distribution, intra-specific competition and commerical fishing activities. We quantified the foraging habitat preferences of Scopoli's Shearwater Calonectris diomedea in the Mediterranean Sea. We analysed habitat preferences in relation to a suite of physical and ecological variables including sea depth, net primary production and distance to other colonies (as a proxy of intra-specific competition). Since the Mediterranean is heavily impacted by commercial fisheries, we also incorporated the distance to fishing harbours in our analyses as a proxy of the availability of discards which are a potential feeding source for Scopoli's Shearwater. Foraging birds preferred shallower waters and avoided areas close to other colonies, thereby reducing interactions with conspecifics. We also found that long-distance trips were undertaken to areas close to fishing harbours, suggesting that these represented particularly profitable locations to compensate for the greater travelling costs involved. No differences in foraging between the sexes were recorded. This study improves our understanding of the at-sea distribution and habitat preference of a seabird inhabiting the over-exploited Mediterranean Sea. Our results support growing evidence that seabirds exhibit complex relationships with commerical fishing activities, which must be considered when planning conservation programmes.
TL;DR: This article examined the relationship between FAD and MAD in 28 summer migrant bird species over a 42-year period (1970-2011) at Portland Bird Observatory, UK and found that the relationship was weak, particularly in long-distance migrants.
Abstract: As the climate changes, many long-term studies have shown that the timing of bird migration is shifting, increasing the need for reliable measures of migratory phenology. Ideally, daily counts of birds at a site are used to calculate the mean arrival date (MAD) but, as this approach is not always possible and is very labour-intensive, simpler metrics such as first arrival date (FAD) have commonly been used. Here, we examine the relationship between FAD and MAD in 28 summer migrant bird species over a 42-year period (1970–2011) at Portland Bird Observatory, UK. Although significant correlations between FAD and MAD were detected, relationships were weak, particularly in long-distance migrants. We suggest that FAD, although a simple and straightforward measure, is not particularly robust as a proxy for overall migratory phenology at a population level.
TL;DR: This investigation investigates the reproductive performance of Tengmalm’s Owls Aegolius funereus in a temperate and a boreal population in relation to long-term variations in the abundance of their main prey (small rodents).
Abstract: Environmental variation across space and time can strongly influence life-history strate-gies in vertebrates. It has been shown that the reproductive success of birds of prey isclosely related to food availability. However, relatively little is known about intraspecificdifferences in reproductive success of birds in relation to varying ecological conditionsacross environmental gradients. We investigated the reproductive performance of Teng-malm’s Owls Aegolius funereus in a temperate (Czech Republic, 50°N) and a boreal (Fin-land, 63°N) population in relation to long-term variations in the abundance of theirmain prey (small rodents). Prey densities at the northern site were much higher, butthere were also large inter-annual fluctuations and years with steep summer declines ofvole densities. Northern owls laid larger clutches but offspring production per nest wassimilar at both study sites. This resulted from higher nestling mortality in the northernpopulation, especially in nests established later in the season. Despite much greater nest-ing losses due to predation by Pine Martens Martes martes, productivity at the popula-tion level was about four times greater at the temperate site, mainly due to the muchhigher breeding densities compared with Finland. Tengmalm’s Owls at the temperatestudy site may benefit from relatively stable prey abundance, a more diverse prey com-munity that offers alternative prey during vole scarcity, longer nights in summer thatallow more time for foraging, and a lower level of interspecific competition with othervole-specialized predators.Keywords: Aegolius funereus, Boreal Owl, life history, nesting success, predator–prey dynamics,prey abundance, reproductive strategy, seasonal decline.A central issue of evolutionary ecology is to under-stand how and why life-history traits vary acrossgeographical regions, both among and within spe-cies (Martin 2004). In birds, one of the most con-sistent patterns of variability in reproductivestrategies, illustrated both within and across spe-cies, is the latitudinal increase in clutch size (Lack1968, Klomp 1970, Jetz et al. 2008, Griebeleret al. 2010). At a species level, populations occur-ring in different parts of the range often facecontrasting ecological conditions; these local condi-tions can modify the selective pressures affectinglife-history characteristics, which in turn may leadto variation in reproductive strategies (Tieleman2009). Dark-eyed Juncos Junco hyemalis, whichbreed in North America across an extensive altitu-dinal gradient (Bears et al. 2009), provide a text-book example of within-species variation in lifehistories. Juncos inhabiting high elevations start tobreed later and their reproductive season is con-stricted so that on average they are able to raiseonly half the number of young compared withconspecifics living at lower elevations. Lower
TL;DR: The use of lighter transmitters and a reduction of handling time, particularly during the breeding season, are suggested as essential improvements in procedure to reduce the mortality risk associated with the capture, handling and tagging of these vulnerable species.
Abstract: Capturing and marking free-living birds permits the study of important aspects of their biology but may have undesirable effects. Bird welfare should be a primary concern, so it is necessary to evaluate and minimize any adverse effects of procedures used. We assess short-term effects associated with the capture, handling and tagging with backpack-mounted transmitters of Pin-tailed Pterocles alchata and Black-bellied Pterocles orientalis Sandgrouse, steppe birds of conservation concern. There was a significantly higher mortality (15%) during the first week after capture than during the following weeks (< 2.5%) in Pin-tailed Sandgrouse, but no significant temporal mortality pattern in Black-bellied Sandgrouse. In Pin-tailed Sandgrouse, mortality rate during the first week increased with increasing relative transmitter and harness weight regardless of season, and with increasing handling time during the breeding season. There were no significant differences in mortality rate between study areas, type of tag, sex or age or an effect of restraint time. These results suggest the use of lighter transmitters (< 3% of the bird’s weight) and a reduction of handling time (< 20 min), particularly during the breeding season, as essential improvements in procedure to reduce the mortality risk associated with the capture, handling and tagging of these vulnerable species.
TL;DR: In this article, the authors constructed DNA profiles for 271 individual birds using a collection of over 1600 moulted feathers collected from 148 territories, representing 34% of known Scottish territories in the largest population genetic study of Golden Eagles undertaken to date.
Abstract: Conservation management of species distributed across fragmented habitats requires consideration of population genetic structure and relative levels of genetic diversity throughout the relevant geographical range The Golden Eagle Aquila chrysaetos is monitored within Scotland to ensure its survival in the face of land-use pressure, persecution and future climate change In this study we constructed DNA profiles for 271 individual birds using a collection of over 1600 moulted feathers collected from 148 territories, representing 34% of known Scottish territories in the largest population genetic study of Golden Eagles undertaken to date The results, based on data from 10 nuclear microsatellite loci, revealed previously unreported genetic structure between the islands of the Outer Hebrides and the rest of Scotland (FST = 003), together with evidence of reduced genetic diversity in the Outer Hebridean population compared with mainland Scotland Analysis of gene flow supports a hypothesis of limited, predominantly male-mediated, dispersal from the Outer Hebrides to mainland Scotland The persistence of this pattern is discussed with respect to variation in population density and persecution pressure across Scotland A finding of non-random mating within the Outer Hebrides is interpreted as evidence of natal philopatry that was revealed by more intensive sampling in these islands, and is likely to be accentuated by the apparent degree of isolation of the islands from the rest of Scotland
TL;DR: The findings suggest that adaptation of PBM in response to climate-mediated changes in the timing and duration of the breeding season is possible, however, the requirement to complete PBM prior to migration or the onset of winter might constrain the extent to which breeding seasons can lengthen, especially for later nesting species.
Abstract: Higher temperatures resulting from climate change have led to predictions that the duration of the breeding season of many temperate bird species may be changing. However, the extent to which breeding seasons can be altered will also depend on the degree of flexibility in processes occurring at other points in the annual cycle. In particular, plasticity in the timing of post-breeding moult (PBM) could facilitate changes in the timing of key events throughout the annual cycle, but little is known about the level of within- and between-species plasticity in PBM. As part of the British Trust for Ornithology (BTO) Ringing Scheme, many ringers routinely record moult scores of flight feathers, and these can be used to provide information on the annual progression of PBM for a range of species. Here we use ringing data to investigate patterns of PBM in 15 passerines, as well as data from the BTO Nest Record Scheme to relate these differences to the timing of breeding of these species across the UK. We find considerable variation in both the mean start (19 May–29 July) and duration (66–111 days) of PBM between species, but find no evidence that species starting PBM later in the season complete it any faster. However, there is considerable within-species variation in PBM, particularly for multi-brooded species; PBM starts later and is completed in less time when the duration of the breeding season (difference between first and last nests) is longer. This implies that a later end to breeding can be compensated for by faster PBM, and that advances in breeding could lead to earlier and slower PBM. Our findings suggest that adaptation of PBM in response to climate-mediated changes in the timing and duration of the breeding season is possible. However, the requirement to complete PBM prior to migration or the onset of winter might constrain the extent to which breeding seasons can lengthen, especially for later nesting species.