Showing papers by "Keith A. Hobson published in 2010"

Conserving migratory land birds in the new world: do we know enough?

Abstract: Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences on fitness and the importance of habitat on the breeding grounds used after breeding. Although detailed investigations have shed light on the ecology and population dynamics of a few avian species, knowledge is sketchy for most species. Replication of comprehensive studies is needed for multiple species across a range of areas, Information deficiencies are even greater during the wintering season, when birds require sites that provide security and food resources needed for survival and developing nutrient reserves for spring migration and, possibly, reproduction. Research is needed on many species simply to identify geographic distributions, wintering sites, habitat use, and basic ecology. Studies are complicated, however, by the mobility of birds and by sexual segregation during winter. Stable-isotope methodology has offered an opportunity to identify linkages between breeding and wintering sites, which facilitates understanding the complete annual cycle of birds. The twice-annual migrations are the poorest-understood events in a bird's life. Migration has always been a risky undertaking, with such anthropogenic features as tall buildings, towers, and wind generators adding to the risk. Species such as woodland specialists migrating through eastern North America have numerous options for pausing during migration to replenish nutrients, but some species depend on limited stopover locations. Research needs for migration include identifying pathways and timetables of migration, quality and distribution of habitats, threats posed by towers and other tall structures, and any bottlenecks for migration. Issues such as human population growth, acid deposition, climate change, and exotic diseases are global concerns with uncertain consequences to migratory birds and even less-certain remedies. Despite enormous gaps in our understanding of these birds, research, much of it occurring in the past 30 years, has provided sufficient information to make intelligent conservation efforts but needs to expand to handle future challenges.

Recent advances in understanding migration systems of New World land birds

Abstract: Our understanding of migratory birds' year-round ecology and evolution remains patchy despite recent fundamental advances. Periodic reviews focus future research and inform conservation and management; here, we take advantage of our combined experiences working on Western Hemisphere avian migration systems to highlight recent lessons and critical gaps in knowledge. Among topics discussed are: (1) The pipeline from pure to applied researchers leaves room for improvement. (2) Population limitation and regulation includes both seasonal and between-season interactions. (3) The study of movements of small-bodied species remains a major research frontier. (4) We must increase our understanding of population connectivity. (5) With few exceptions, population regulation has barely been investigated. (6) We have increasingly integrated landscape configuration of habitats, large-scale habitat disturbances, and habitat quality impacts into models of seasonal and overall demographic success. (7) The post-breeding seas...

Using Isoscapes to Track Animal Migration

Abstract: Movement patterns and annual migrations of animals are vital components of their ecology but have generally been poorly studied due to fundamental limitations in using exogenous markers. Stable isotope measurements of animal tissues represent endogenous markers that can provide information on origins because they reflect isoscape patterns occurring at various scales. In cases where animals move among isotopically distinct regions or over isotopic gradients, the isotopic measurement of a tissue representing the appropriate period of dietary integration can be used to place animals spatially and temporally. Detailed information on animal ranges, isoscape pattern and the dynamics of isotopic turnover in various tissues allows the placement of individuals or populations to solution space within isoscapes. Basic principles and examples of tracking migratory animals using stable isotopes are provided with particular emphasis on the use of the stable isotopes of the elements C, N, H, O and Sr. Improvements in our understanding of the factors causing annual deviations from isoscape patterns based on long-term datasets are needed to improve resolution of placing animals to origins.

Changes in diet and trophic position of a top predator 10 years after a mass mortality of a key prey

Abstract: Chiaradia, A., Forero, M. G., Hobson, K. A., and Cullen, J. M. 2010. Changes in diet and trophic position of a top predator 10 years after a mass mortality of a key prey. - ICES Journal of Marine Science, 67: 1710-1720.After the disappearance of primary prey, seabirds exhibit gradually decreased breeding performance, and eventually the population size drops. Results are presented of an investigation into the diet of little penguins (Eudyptula minor) at Phillip Island, Australia, during a period when their key prey, pilchard (Sardinops sagax), declined dramatically. Data from stomach flushing (1982-2006) were used, supported by stable isotope (δ 15 N, δ 13 C) analyses of blood samples (2003, 2004, and 2006). The effect of the pilchard mortality on penguin diet was immediate, the birds shifting to a diet almost devoid of pilchard, and this was followed by 2 years of low breeding success, with considerably fewer penguins coming ashore. During periods when pilchard was not part of the diet, penguins consumed prey of a higher trophic level, e.g. higher values of δ 15 N. Variability in penguin blood δ 15 N coincided with years of low prey diversity. The disappearance of pilchard resulted in a decrease in prey diversity and led penguins to “fish up” the foodweb, possibly because of the simplified trophic structure. After 1998, however, breeding success re-attained average levels and the numbers of penguins coming ashore increased, probably because of increased abundance of prey other than pilchard after a 3-year period of food scarcity. Although little penguins apparently compensated over time, a less-flexible diet could make them ultimately vulnerable to further changes in their foodweb.

Influence of forage preferences and habitat use on 13C and 15N abundance in wild caribou (Rangifer tarandus caribou) and moose (Alces alces) from Canada.

Abstract: Stable isotope composition (δ13C and δ15N) of moose (Alces alces) and caribou (Rangifer tarandus) hair from the boreal forest of Jacques-Cartier Park and Cote-Nord (Quebec) and arctic tundra of Queen Maud Gulf and Southampton Island (Nunavut) was investigated as an indicator of dietary preferences and habitat use. Values of δ13Chair and δ15Nhair in moose were consistently lower compared to those of caribou. This is consistent with the depletion in 13C and 15N in the plants preferred by moose, essentially browse (shrub and tree leaves), compared to caribou forage, which included significant amounts of graminoids, lichen and fungi. The δ13Chair values of caribou differed between closed boreal forest and open-tundra ecosystems. This pattern followed that expected from the canopy effect observed in plant communities. Variation in δ15Nhair values of caribou was probably linked to the effect of different climatic conditions on plant communities. This study underlines the potential of isotopic analysis for studi...

Spring arrival along a migratory divide of sympatric blackcaps (Sylvia atricapilla).

Abstract: The recent formation of a migratory divide in the blackcap (Sylvia atricapilla) involves sympatrically breeding birds migrating to different overwintering quarters. Within the last 50 years, a novel migratory strategy has evolved resulting in an increasing proportion of birds now wintering in Britain instead of migrating to the traditional sites in the Mediterranean area. This rapid microevolution has been attributed to allochronic spring arrival of migrants from the respective wintering quarters leading to assortative mating. Moreover, blackcaps wintering in Britain may experience fitness advantages owing to improved local wintering conditions. We used stable hydrogen isotope signatures (δD) to scrutinize the degree of temporal segregation of blackcaps upon spring arrival and to test for carry-over effects in body condition associated with the disparate wintering environments. Although we found that migrants from Britain arrive significantly earlier on German breeding grounds than migrants from the Mediterranean region, we also found a considerable overlap in arrival times. In a resampling model, the mean probability of assortative mating of birds wintering in Britain is ≤28% in both years. These results suggest that allochrony alone is not a strong isolating barrier between the two subpopulations. Migrants from both wintering locations did not differ in terms of body mass, mass-tarsus residuals or mass-tarsus ratio and arrived in a similar reproductive disposition. Thus, blackcaps wintering in Britain do not gain an apparent fitness advantage on spring migration due to carry-over effects in body condition. Future studies should explore additional factors such as differences in song quality and habitat that might contribute to the rapid microevolution of the blackcap.

Temporal and spatial patterns in the diet of northern fulmars Fulmarus glacialis in the Canadian High Arctic

Abstract: AQUATIC BIOLOGY Aquat Biol Vol. 10: 181–191, 2010 doi: 10.3354/ab00277 Published online August 31 Temporal and spatial patterns in the diet of northern fulmars Fulmarus glacialis in the Canadian High Arctic M. L. Mallory 1, *, N. J. Karnovsky 2 , A. J. Gaston 3 , K. A. Hobson 4 , J. F. Provencher 5 , M. R. Forbes 6 , G. L. Hunt Jr. 7 , T. Byers 8 , T. A. Dick 9 Canadian Wildlife Service, Box 1714, Iqaluit, Nunavut X0A 0H0, Canada Department of Biology, Pomona College, 175 W. 6th St., Claremont, California 91711, USA National Wildlife Research Centre, Environment Canada, Carleton University, Ottawa, Ontario K1A 0H3, Canada Environment Canada, 11 Innovation Blvd., Saskatoon, Saskatchewan SYN 3H5, Canada Department of Biology, University of Victoria, Victoria, British Columbia V8W 3N5, Canada Department of Biology, Carleton University, Ottawa, Ontario K1S 5B6, Canada Department of Ecology and Evolutionary Biology, University of California – Irvine, Irvine, California 92697, USA Byers Environmental Studies, Box 1049, Teulon, Manitoba R0C 3B0, Canada Department of Zoology, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada ABSTRACT: The northern fulmar Fulmarus glacialis is a medium-sized seabird with a broad, circum- polar range in the northern hemisphere, and is the only petrel that inhabits the High Arctic. We used stomach analysis and stable isotopes (δ 15 N, δ 13 C) of muscles to examine the diet of 179 fulmars dur- ing the breeding season at 4 locations in Arctic Canada, to compare diet to those from studies con- ducted in these regions > 2 decades earlier. Across sampling locations, cephalopods, polychaetes and crustaceans dominated dietary remains in fulmars, although there was some regional variation. Both stable isotopes and stomach dissections showed that a seasonal shift in diet occurred in May, after which fulmars fed at a higher trophic level, suggesting a difference in winter/migration diet and breeding season diet. After migration, fulmar digestive organs decreased markedly in size, and by the time chicks were hatching, these organs were still 17 to 39% smaller than their size when birds arrived at the colony. Despite ongoing changes in the marine environment in much of the Arctic due to global warming, recent fulmar diet samples were similar to samples collected in the 1970s and 1980s, except that a higher proportion of recent collections contained fish. KEY WORDS: Arctic · Cephalopod · Crustacean · Procellariiformes · Reproduction Resale or republication not permitted without written consent of the publisher INTRODUCTION Invertebrate and fish fauna vary across oceano- graphic zones in the North Atlantic in response to differing oceanographic conditions, often on small geographic scales (e.g. Karnovsky et al. 2003). Many marine birds are generalist predators that exploit invertebrates and fish (e.g. Woo et al. 2008). Conse- quently, monitoring the diet of marine birds provides a measure of the diversity and availability of different types of organisms in marine food webs and allows detection of shifts in food webs due to changes in oceanographic conditions (e.g. Gaston et al. 2003, Frederiksen et al. 2004, 2006). In the North Atlantic, the northern fulmar Fulmarus glacialis is the only Procellariiform seabird (petrel) found in Boreal, Low Arctic and High Arctic oceano- graphic zones (Salomonsen 1965, Hatch & Nettleship 1998). It feeds on zooplankton, cephalopods, fish and carrion across its range in Boreal and Low Arctic waters (Furness & Todd 1984, Hamer et al. 1997, Phillips et al. 1999, Garthe et al. 2004). Relatively less is known about *Email: mark.mallory@ec.gc.ca © Inter-Research 2010 · www.int-res.com

Understanding the migration ecology of European red admirals Vanessa atalanta using stable hydrogen isotopes

Abstract: Tracking migratory movement of small animals with variable migration patterns is difficult with standard mark–recapture methods or genetic analysis. We used stable hydrogen isotope (δD) measurements of wings from European red admirals Vanessa atalanta to study several aspects of this species’ migration. In the central part of southern Europe we found large differences in δD values between red admirals sampled in autumn and spring supporting the hypothesis that reproduction takes place in the Mediterranean region during winter. There was also an apparent influx to southern Europe in the spring of individuals with a more southerly origin, since many samples had higher δD values and similar to those expected from coastal areas of North Africa. We found a clear seasonal difference in the δD values of red admirals sampled in northern Europe. Spring migrants arriving in northern Europe generally had high δD values that indicated a southerly origin. In autumn, δD values suggested that red admirals were mostly from regions close to the sampling sites, but throughout the sampling period there were always individuals with δD values suggesting non-local origins. The migration pattern of this species is supposedly highly variable and plastic. δD differences between individuals in the western part of Europe were generally small making migratory patterns difficult to interpret. However, butterflies from western Europe were apparently isolated from those from north-eastern Europe, since δD values in the western region rarely corresponded to those of autumn migrants from the north-east. Use of δD data for inferring butterfly migration in Europe is complex, but our study showed that this technique can be used to help uncover previously unknown aspects of red admiral migration.

Migratory Connectivity in the Rusty Blackbird: Isotopic Evidence From Feathers of Historical and Contemporary Specimens

Abstract: . The Rusty Blackbird (Euphagus carolinus) has declined dramatically across its range in North America since at least the 1960s, but the causes for this decline are unknown. We measured ratios of stable hydrogen isotopes (δD) in feathers collected from Rusty Blackbirds wintering in the Mississippi Alluvial Valley (n = 255 birds) and the coastal plain of South Carolina and Virginia (n = 281 birds), 2005–2009, to estimate the region of origin of birds wintering west and east of the Appalachians, respectively. We also measured δD values in feathers from all available museum specimens collected from 1879 to 1990 in these same two regions (n = 190 birds). Isotopic values support migratory connectivity in this species with breeding populations in the western and central boreal forest migrating through a central or Mississippi flyway and those breeding in the eastern boreal forest migrating to a winter range east of the Appalachians. We detected little long-term change in the breeding origins of modern a...

Linking Canadian Harvested Juvenile American Black Ducks to Their Natal Areas Using Stable Isotope (δD, δ13C, and δ15N) Methods

Abstract: Understanding source-sink dynamics of game birds is essential to harvest and habitat management but acquiring this information is often logistically and financially challenging using traditional methods of population surveys and banding studies. This is especially true for species such as the American Black Duck ( Anas rubripes ), which have low breeding densities and extensive breeding ranges that necessitate extensive surveys and banding programs across eastern North America. Despite this effort, the contribution of birds fledged from various landscapes and habitat types within specific breeding ranges to regional harvest is largely unknown but remains an important consideration in adaptive harvest management and targeted habitat conservation strategies. We investigated if stable isotope ( D, 13C, 15N) could augment our present understanding of connectivity between breeding and harvest areas and so provide information relevant to the two main management strategies for black ducks, harvest and habitat management. We obtained specimens from 200 hatch-year Black Duck wings submitted to the Canadian Wildlife Service Species Composition Survey. Samples were obtained from birds harvested in Western, Central, and Eastern breeding/harvest subregions to provide a sample representative of the range and harvest rate of birds harvested in Canada. We sampled only hatch-year birds to provide an unambiguous and direct link between production and harvest areas. Marine origins were assigned to 12%, 7%, and 5% of birds harvested in the Eastern, Central, and Western subregions, respectively. In contrast, 32%, 9%, and 5% of birds were assigned, respectively, to agricultural origins. All remaining birds were assigned to nonagricultural origins. We portrayed probability of origin using a combination of Bayesian statistical and GIS methods. Placement of most eastern birds was western Nova Scotia, eastern New Brunswick, Prince Edward Island, and southern Newfoundland. Agricultural birds from the Central region were consistent with the Saguenay region of Quebec and the eastern claybelt with nonagricultural birds originating in the boreal. Western nonagricultural birds were associated with broad boreal origins from southern James Bay to Lake of the Woods and east to Cochrane, Ontario. Our work shows that the geographic origins, landscape, and habitat associations of hatch-year Black Ducks can be inferred using this technique and we recommend that a broad-scale isotopic study using a large sample of Canadian and US harvested birds be implemented to provide a continental perspective of source-sink population dynamics.

Arctic waders and the capital-income continuum: Further tests using isotopic contrasts of egg components

Abstract: Birds migrating annually to high-latitude breeding grounds may benefit from the transport of endogenous nutrient reserves that ultimately contribute to reproduction. Shorebirds represent a diverse group of Arctic breeders that typically arrive on the breeding grounds with body reserves enriched in 13C and 15N due to wintering and staging in marine or estuarine habitats. Such isotopic differences between endogenous macronutrient reserves and local foodwebs allow the use of stable isotopes to test for the source of nutrient allocations to eggs. We examined δ13C and δ15N values in lipid-free yolk and albumen and δ13C values in yolk lipid of first clutches of ten species of sandpiper and plover breeding near Churchill, Manitoba, Canada in 2003. Most birds had egg isotope values indicating a C3 terrestrial biome, which fits primarily an income (exogenous) breeding strategy. Two exceptions were single sandpiper and plover with strong marine isotope values. Among species, strong positive relationships for each isotope between egg tissue components suggest that egg proteins and lipids tended to be derived from the same isotopic source. Correlations of egg δ13C values for lipids and proteins approached theoretical relationships expected for exogenous breeding strategies, based on captive studies. Significant positive correlations between clutch initiation date and δ13C values of egg lipids and albumen suggest some endogenous nutrient contributions to later laid eggs but the circumstances under which this may occur are unstudied. Where possible, we recommend that researchers use blood and fat biopsies from laying females as a means of anchoring endogenous and exogenous endpoints for modeling of each reproductive event. We encourage the isotopic analysis of egg albumen, yolk and yolk lipids among individuals and species and tests of correlations among these components as a means of inferring origins of nutrients to eggs.

Migratory connectivity in a declining bird species: using feather isotopes to inform demographic modelling

Abstract: Aim Conservation programmes for endangered migratory species or populations require locating and evaluating breeding, stopover and wintering areas We used multiple stable isotopes in two endangered European populations of wrynecks, Jynx torquilla L, to locate wintering regions and assess the degree of migratory connectivity between breeding and wintering populations Location Switzerland and Germany Methods We analysed stable nitrogen (d 15 N), carbon (d 13 C) and hydrogen (dD) isotopes from wing feathers from two populations of wrynecks to infer their wintering origins and to assess the strength of migratory connectivity We tested whether variation in feather isotopic values within the Swiss population was affected by bird age and collection year and then considered differences in isotopic values between the two breeding populations We used isotopic values of summer- and winter-grown feathers to estimate seasonal distributions Finally, we calculated a species-specific dD discrimination factor between feathers and mean annual dD values to assign winter-grown feathers to origin Results Bird age and collection year caused substantial isotopic variation in winter-grown feathers, which may be because of annually variable weather conditions, movements of birds among wintering sites and/or reflect asynchronous moulting or selection pressure The large isotopic variance in winter-grown feathers nevertheless suggested low migratory connectivity for each breeding population, with partially overlapping wintering regions for the two populations Main conclusions Isotopic variance in winter-grown feathers of two breeding populations of wrynecks and their geographical assignment point to defined, albeit overlapping, wintering areas, suggesting both leapfrog migration and low migratory connectivity On this basis, integrative demographic models can be built looking at seasonal survival patterns with links to local environmental conditions on both breeding and wintering grounds, which may elucidate causes of declines in migratory bird species

Stable isotopes link diet to avian yolk carotenoid allocation: a comparative study of five auk species (Charadriiformes: Alcidae).

Abstract: The allocation of important but environmentally limited nutrients, such as carotenoids, often represents a trade‐off between homeostasis and reproduction. However, key questions remain about how diet and species traits influence carotenoid allocation. We studied yolk carotenoid profiles and yolk color in relation to trophic level (based on δ15N values) in five species of seabirds belonging to the family Alcidae: common murre (Uria aalge), pigeon guillemot (Cepphus columba), Cassin’s auklet (Ptychoramphus aleuticus), rhinoceros auklet (Cerorhinca monocerata), and tufted puffin (Fratercula cirrhata). In three species, which ranged from low (tufted puffin) to high (pigeon guillemot) trophic level, yolks had pink to red hues and contained exclusively astaxanthin, while yolks of species from a high trophic level (common murre) and from a generalist forager (rhinoceros auklet) had yellow to orange hues and contained astaxanthin, lutein, and zeaxanthin. The absence of a systematic relationship between t...

Comparing the predictive capability of forest songbird habitat models based on remotely sensed versus ground-based vegetation information

Abstract: Habitat suitability models allow for predictive modeling of the supply of wildlife habitat through time under various forest harvesting scenarios. These models often rely on remotely sensed data in...

Food and feeding ecology of the Tasmanian short-tailed shearwater (Puffinus tenuirostris, Temminck): insights from three complementary methods

Abstract: The diet of seabirds is usually studied by the identification of prey items recovered from their stomachs. This method is however limited to recently ingested prey and to non-digestible hard parts, precluding the determination of marine resources consumed by birds during long foraging trips. Thus, alternative indirect approaches are necessary to assess the potential importance of digested prey from long-term foraging activity. In this study, we present three complementary techniques to determine the prey of breeding short-tailed shearwaters (Puffinus tenuirostris) when they feed for themselves during long foraging trips: (1) conventional food analysis, (2) stable isotope analysis of carbon and nitrogen signatures (δ13C and δ15N) of plasma, and (3) lipid analysis of stomach oil and the use of fatty acids and fatty alcohols as trophic markers (stomach oil is of dietary origin). Dietary analysis showed that fish dominated by mass over crustaceans (82 and 18%, respectively). Two euphausiids Euphausia vallentini (a sub-Antarctic species) and Nyctiphanes australis (a Tasmanian species), and fish postlarvae represented more than 94% of the total number of food items, with myctophid fish of larger size dominating by mass. Plasma isotopic signature of birds suggested that shearwaters foraged mainly in Antarctic waters (δ13C = -23.8‰), and fed at a trophic level close to that of a myctophid-eater, the king penguin (δ15Nshort-tailed shearwater = 8.7‰, δ15Nking penguin = 9.8‰). Comparisons between fatty -acid and -alcohol patterns of stomach oil wax esters with those of potential prey also suggested a food based on myctophids (Electrona antarctica, Krefftichthys anderssoni and Gymnoscopelus braueri). To conclude, both lipid and stable isotope methods emphasized the importance of myctophids in the nutrition of short-tailed shearwaters during the chick-rearing period when adult birds feed for themselves. This study illustrates the interest of using both direct and indirect methods to determine trophic relationships between marine organisms.

Deuterium (δD) in Feathers of Mongolian Waterbirds Uncovers Migratory Movements

Abstract: . The need for better understanding of migratory movements of wild birds in Asia promoted an evaluation of the usefulness of deuterium in feathers (δDf) to assign origins. Feathers were sampled from Bar-headed Geese (Anser indicus), Whooper Swans (Cygnus cygnus), Mongolian Gulls (Larus vegae mongoliens), Curlew Sandpipers (Calidris ferruginea) and Pacific Golden Plover (Pluvialis fulva) in north-central Mongolia, from June to September 2007. Univariate statistical analyses were performed to test for differences between study sites for all species and between growing (blood) and previously grown (non-blood) feathers only for Bar-headed Geese. Values of δDf in actively growing feathers generally agreed with those expected from integrated isotopic signals in precipitation expected for sampling sites. Values of δDf from adult migrant birds also indicated varying degrees of movement from north to south expected from the movement of these species in Asia. These results show promise for the isotope appro...

Isotope forensic analysis does not support vagrancy for a Marbled Duck shot in Essex

Abstract: Analysis of the stable-hydrogen isotope content (δD) of feathers taken from a first-winter Marbled Duck Marmaronetta angustirostris shot in Essex on 1st September 2007 showed little difference between juvenile feathers grown at the natal site and those grown during the post-juvenile moult. The δD values of both groups of feather were similar to those expected if the bird had grown feathers in coastal areas of northern Europe, but differed significantly from those in feathers from known wild individuals taken from the species' nearest breeding areas, in Spain. These results suggest that the bird originated from outside of the normal breeding range of the species and was most likely to have been of captive origin.

Linking breeding and wintering areas of ‘northern trumpeting’ Bullfinches Pyrrhula p. pyrrhula by colour‐rings and deuterium stable isotopes

Abstract: Capsule: Feather stable isotope analysis suggests summering of so‐called ‘northern trumpeting’ Bullfinches in Denmark.

Reply to Urquhart: Conservation of migratory double breeders

Abstract: Urquhart (1) raises additional potential conservation implications of our discovery of migratory double breeding in several Neotropical migrants (2) and suggests that source sink thinking is not appropriate for this situation. We fully agree.