Showing papers in "The Condor in 1998"
TL;DR: In this paper, the authors compared the avifauna in two cities, Quebec (Canada) and Rennes (France), in order to define general responses of wildlife in an urban ecosystem.
Abstract: We compared the avifauna in two cities, Quebec (Canada) and Rennes (France), in order to define general responses of wildlife in an urban ecosystem. These cities have a similar urban structure that permits investigation along an urbanization gradient from downtown to rural residential areas. However, they are in opposite temperate climate and imbedded in a forested and an agricultural landscape, respectively. Plots ranging from 10 to 20 ha were surveyed in winter and spring by recording all birds seen or heard. Most plots could be located along a gradient according to proportions of vegetated open space. Both the Shannon-Wiener and Simpson indices of diversity indicated a pattern of increasing diversity from most to least urbanized areas in spring. Winter species diversity and richness was low in Quebec compared to Rennes, reflecting the much harsher winter conditions in Quebec. Breeding densities of House Sparrows (Passer domesticus) and European Starlings (Sturnus vulgaris) were quite similar in Quebec and Rennes, as were densities of European Blackbirds (Turdus merula) and its ecological equivalent in Quebec, the American Robin (Turdus migratorius). The type of surrounding landscape can not explain the variation of species numbers within the city. If we examine the urban environment as a new ecological system rather than a degraded environment, we can regroup birds in two major species groups: the omnivorous species adapted to the urban environment and its particular food resources such as garbage and the species that find, in the urban environment, resources which they normally exploit in their usual habitat.
487 citations
TL;DR: It is suggested that postfledging movements in Wood Thrushes are keyed by the availability of food resources and the presence of conspecifics, although other factors may play a role.
Abstract: We monitored 42 radio-tagged, fledgling Wood Thrushes (Hylocichla mustelina) to investigate movement and habitat use during the postfledging period Fledglings' mean (± SE) age at dispersal from the natal sites was 325 ± 06 days post hatching First dispersal sites were located 15 ± 03 km from the natal site All young joined flocks of juveniles, except three birds that remained solitary Sixteen birds stayed at the first dispersal site until departure on migration, whereas nine visited additional dispersal sites On 40 occasions, 15 fledglings moved up to 6 km from their dispersal sites Before late August, 967% of fledglings' locations occurred in: (1) second growth scrub/deciduous sapling sites located along forest borders and abandoned farms (594%), (2) gypsy moth (Lymantria dispar) damaged deciduous forest (244%), and (3) Virginia pine (Pinus virginianus) forest with heavy deciduous understory (128%) Fruiting trees and shrubs used as food sources by juveniles fruit earlier in these habitats After late August, an increased number of fledgling locations (141%) occurred in mature deciduous or mixed forest, possibly tracking the later fruiting cycles of understory plants in these habitats Twenty-four of 33 fledglings left the study area in September Mean age at departure was 81 ± 5 days post hatching We suggest that postfledging movements in Wood Thrushes are keyed by the availability of food resources and the presence of conspecifics, although other factors may play a role We conclude that successful conservation of migratory species requires protection of habitats used during the postfledging period as well as those used during the nesting portion of the life cycle
207 citations
TL;DR: Rates of predation were highest in small woodlots and declined with increasing forest patch size consistent with the trend reported for active nests on the same sites, with the amount of variation highest on sites with high predation rates.
Abstract: Artificial nests frequently are used to assess levels and patterns of nest predation, but how well these nests measure rates of predation or trends in predation rates at real nests is unclear. We compared predation rates between 58 active Wood Thrush (Hylocichla mustelina) nests paired with 58 artificial nests designed to resemble Wood Thrush nests. Paired nests were available to the same predator community both spatially and temporally. Rates of nest predation were significantly lower for active Wood Thrush nests (33%) than for artificial nests (64%). Rates of parasitism by Brown-headed Cowbirds (Molothrus ater) also differed between the two groups. Twenty-six percent of active nests and none of the artificial nests were parasitized by cowbirds. During 1993 and 1994, we conducted three artificial nest trials on six study sites per year. Rates of predation were highest in small woodlots and declined with increasing forest patch size consistent with the trend reported for active nests on the same sites. Within sites, rates of predation varied among trials with the amount of variation highest on sites with high predation rates. Our results suggest that although artificial nests should not be used to measure actual rates of nest predation or parasitism, they may be valuable for detecting trends in rates of predation. However, because there are many potential biases associated with the use of artificial nests that may make interpretation of trend data difficult, we recommend using artificial nests primarily in pilot studies or in conjunction with active nests.
175 citations
TL;DR: The timing of arrival from spring migration was studied in 4 years for male Pied Flycatchers in central Spain to determine whether arrival times are consistent within individuals between years and are similar between relatives.
Abstract: The timing of arrival from spring migration was studied in 4 years for male Pied Flycatchers (Ficedula hypoleuca) in central Spain. Heritability and repeatability analyses were performed at several levels of familial resemblance and male age in order to determine whether arrival times are consistent within individuals between years and are similar between relatives. Oldest males arrived earlier. Arrival time explained much of the variation in laying time and number of young fledged. Age-independent variation in wing length also affected arrival date, the males with longest wings settling earlier. Arrival times were not repeatable within individuals across years and were not similar between relatives (parents-sons, full-sibs). Although genetic variation may exist in departure dates of long-distance migrant birds, the close connection of an early arrival to high reproductive success may have depleted genetic variation in arrival time. In addition, environmental variation probably is too high to detect significant heritability in arrival times without very large sample sizes.
134 citations
TL;DR: It is found that observing parrots from the canopy is a useful method for quantifying parrot activities in a closed-canopy system, and that these forest-dwelling parrots are markedly less social than their counterparts on islands and in more open habitats.
Abstract: We explored patterns of flight activity, flocking, and habitat use in a diverse community of parrots in an Amazonian lowland forest. Parrots were most active just after sunrise with a second peak of flight activity following a mid-day lull. Brotogeris spp. were exceptional, being most active in the early afternoon. Among the nine genera studied, we observed marked differences in where the birds flew relative to the canopy. Body size was a poor predictor of flight height, although it was strongly and inversely correlated with flock size. Most parrot species flew in groups of one to four individuals, suggesting that mated pairs are stable and that family groups remain together post-fledging. Flocks were exclusively monospecific except when the birds were foraging in trees or eating soil at clay licks. These forest-dwelling parrots did not show dramatic increases in flock size in the evening, reflecting the lack of communal and multispecies roosting observed in other parrots. Generally, the large- and mid-sized species of parrots were associated with high-ground forest, whereas smaller species favored transitional forest. Because daily ranging patterns for these parrots potentially include all habitats, these patterns of habitat use suggest selection for subtle differences among forest types. As expected, smaller species were less detectable at a distance than large species. Comparisons of size and detectability indicate that macaws can be reliably counted to a distance of 300 m, but 100 m may be more appropriate for the smaller and low-flying genera. In sum, we found that observing parrots from the canopy is a useful method for quantifying parrot activities in a closed-canopy system, and that these forest-dwelling parrots are markedly less social than their counterparts on islands and in more open habitats. Patterns of flight behavior, habitat preferences, and the body size to flock size relationship invite further studies on the roles of predation and resource availability in the structuring of parrot communities.
124 citations
TL;DR: In this paper, the authors describe stopover ecology for 132 radiomarked Western Sandpipers (Calidris mauri) relocated repeatedly along the Pacific Flyway of North America.
Abstract: We describe stopover ecology for 132 migrant radiomarked Western Sandpipers (Calidris mauri) relocated repeatedly along the Pacific Flyway of North America. Eighty-eight percent of radiomarked birds were detected at 1-5 sites north of their banding sites, at distances ranging from 240-4,000 km away. We compare length of stay and physical indices of Western Sandpipers banded at coastal sites (San Francisco Bay, California and Grays Harbor, Washington), and an interior, western Great Basin site (Honey Lake, California). Western Sandpipers radiomarked at the interior site had significantly shorter length of stays than birds radiomarked at coastal sites, and they had significantly lower fat scores. The ephemeral nature of Great Basin stopover sites and an increased risk of predation may explain some of this variation. Fat and body condition indexes explained little of the observed variation in length of stay of Western Sandpipers at banding and other stopover sites. Length of stay of birds radiomarked at Grays Harbor were significantly longer compared to birds radiomarked to the south that also stopped at Grays Harbor, suggesting a potential capture effect on length of stay of birds at banding sites. Mean length of stays at seven sites other than banding sites ranged from 1.1-3.3 days and were not significantly affected by sex of bird, year of study, or banding location. Length of stay of male Western Sandpipers at the Copper River Delta, Alaska became significantly shorter later in the migration period, but not for females. Coastal sites along the Pacific Flyway from San Francisco to the breeding grounds generally function as stopovers for Western Sandpipers instead of staging areas.
121 citations
TL;DR: Nest height was positively correlated with concealment at the nest site, supporting the predator-avoidance theory and no other attribute of nest placement differentiated successful nest sites, suggesting that nest predation is likely a function of random events in space and time.
Abstract: We located 511 Acadian Flycatcher (Empidonax virescens) nests in bottomland hardwood forest of eastern Arkansas. Microhabitat characteristics were measured and their relationship with nest success evaluated. Fifty-two percent of all nesting attempts resulted in predation. Attributes of nest placement were similar between successful and unsuccessful nests, although successful nests were placed higher. Similarly, nonparasitized nests were typically higher than parasitized nests. Nests initiated late in the breeding season were placed in larger trees with higher canopy bases resulting in increased vegetation around the nest. Fifteen different tree species were used for nesting. Acadian Flycatchers chose nest trees in a nonrandom fashion, selecting Nuttall oak (Quercus nuttallii) and possumhaw (Ilex decidua) in greater proportions than their availability. However, there was no relationship between tree species used for nesting and nest success. Nest height was positively correlated with concealment at the nest site, supporting the predator-avoidance theory. No other attribute of nest placement differentiated successful nest sites, suggesting that nest predation is likely a function of random events in space and time.
110 citations
TL;DR: This article examined the flight behavior of Common Terns (Sterna &undo) over a nesting colony in Barnegat Bay, New Jersey in 1997 and found that there were no differences in flight behavior as a function of presence and type of craft (motor boat, personal watercraft).
Abstract: I examined the flight behavior of Common Terns (Sterna &-undo) over a nesting colony in Barnegat Bay, New Jersey in 1997. I used the number of birds flying over the colony to test the hypothesis that there were no differences in flight behavior as a function of presence and type of craft (motor boat, personal watercraft). For the overall model, 66% of the variation in the number of terns flying over the colony was explained by breeding period, type of craft, speed, route (established channel or elsewhere), the inter- action of route and speed, and time of day. However, for the early stage of the reproductive cycle, type of craft, speed, and route explained 95% of the variation. Boats that raced elicited the strongest response, as did boats that were outside of the established channel. Boats traveling closer to the nesting colonies elicited stronger responses than those that remained in the channel. Personal watercrafts elicited stronger responses than motor boats. These data suggest that personal watercraft should be managed to reduce disturbance to colonial-nesting species, by eliminating them within 100 m of nesting colonies and restricting speed near such colonies.
107 citations
TL;DR: A survey of California's Central Valley between 1992-1995 documented it as one of the most important regions in western North America to migratory and wintering shorebirds as discussed by the authors, and the most migratory species were found to be the Dunlin (Calidris alpina), Long-billed Dowitcher (Limnodromus scolopaceus), and Killdeer (Charadrius vociferus).
Abstract: Surveys of California's Central Valley between 1992-1995 document it as one of the most important regions in western North America to migratory and wintering shorebirds. Populations averaged 134,000 individuals in August, 211,000 in November, 303,000 in January, and 335,000 in April. Of 33 species, the 10 or 11 that averaged over 1,000 individuals each season accounted for 99% of total numbers. Managed wetlands, agricultural fields (especially rice), and agricultural evaporation ponds held the most shorebirds. Species varied their seasonal, geographic, and habitat use of the Central Valley, primarily in response to changes in water availability from rainfall or management practices and latitudinal variation in habitat availability mediated, in part, by climate. In the record rainfall year of 1994-1995, shorebird numbers increased 74% between November and January, primarily from coast-to-interior movements of the Dunlin (Calidris alpina) and Long-billed Dowitcher (Limnodromus scolopaceus) and local habitat shifts of Killdeer (Charadrius vociferus). Although the Valley's shorebirds face threats from poor or toxic water quality, changing agricultural practices, and habitat loss to urbanization, they should benefit from current efforts to increase flooding of rice fields and to secure a stable high quality water supply for wetlands. Development of a sound conservation strategy is crucial for the preservation of shorebird populations in the Central Valley, as this agriculturally-dominated landscape is among the most altered in North America and remains vulnerable to strong economic and population growth pressures that may impact shorebird habitats in the future.
106 citations
TL;DR: All three groups of predators left all types of egg remains, suggesting that researchers should refrain from classifying nest predators only based on egg remains.
Abstract: We evaluated the consumption of Japanese Quail (Coturnix coturnix) eggs by captive reptiles, birds, and mammals in order to examine potential bias of nest predation experiments, and to determine whether predator identification through egg remains is reliable by the commonly used methods. Because none of the 86 individuals of 22 species of snakes consumed quail eggs in captivity, nest predation may be under-represented in artificial nest experiments. All three groups of predators left all types of egg remains, suggesting that researchers should refrain from classifying nest predators only hy egg remains. The presence of scratches on quail eggs could be considered as a potential tool for reducing small-mouthed mammal bias on predation estimates in small-sized eggs in nest predation experiments.
100 citations
TL;DR: The Galapagos Penguin population has fluctuated, dropping precipitously after the 1982-1983 El Nino and has since then been recovering very slowly as discussed by the authors, and these trends suggest that long-term global climate warming is likely to threaten the population particularly because the population is small and its distribution restricted.
Abstract: The Galapagos Penguin (Spheniscus mendiculus) population probably has always been small and largely restricted to the islands of Fernandina and Isabela. Counts suggest the current population of Galapagos Penguins is likely between 4,250 and 8,500, half of what it was in the early 1970s. Population size has varied and declined probably because of substantial changes in oceanic conditions. Body condition as evidenced by weight is enhanced during cold surface water conditions, La Nina, and deteriorates when surface waters are warmed, El Nino, and under the most severe conditions, penguins starve. Analysis of a long-term data set from counts of the population suggests that the population has fluctuated, dropping precipitously after the 1982-1983 El Nino and has since then been recovering very slowly. This parallels the overall warming in the Pacific during the last 20 years associated with the more frequent El Nino and less frequent La Nina events. These trends suggest that long-term global climate warming is likely to threaten the Galapagos Penguin population particularly because the population is small and its distribution restricted. New threats from climatic warming and increasing human perturbations such as fishing, inadvertent discharge of petroleum products, and transport of potential predators and pathogens to islands increase the risk of extinction.
TL;DR: Mean and minimum concealment did not explain occurrence of predation or brood parasitism for any of the three bird species, and concealment at parasitized versus unparasitized nests and depredated versus fledged nests did not change differently over time.
Abstract: We studied the effect of time and nest-site characteristics on nest concealment measurements and analyzed differences in concealment between parasitized, nonparasitized, depredated, and fledged nests. Mean concealment at nests of three old-field bird species was best explained by bird species, nest plant, and height of the nest. Nests lost concealment over time, particularly those placed high in shrubs or roses (Rosa spp.). Mean and minimum concealment did not explain occurrence of predation or brood parasitism for any of the three bird species, and concealment at parasitized versus unparasitized nests and depredated versus fledged nests did not change differently over time. A literature review showed that most studies of real passerine nests using visual nest concealment have taken measurements after nest termination, and few studies indicated that concealment was important in explaining nest predation or brood parasitism. Late concealment measurements may be an additional source of error in nesting studies, especially if predation or parasitism is more likely to occur at nests sharing similar vegetation characteristics.
TL;DR: It is shown that closed habitat species use significantly higher MAX than their more open habitat relatives, which contrasts with the one reported in studies based on community-wide comparisons, which in general do not correct song data for phylogeny and body mass, or include oscine species.
Abstract: We studied the acoustic frequencies contained in the songs of 44 species of New World doves of eight genera in relation to body mass and habitat structure. On each sonogram, maximum (MAX), minimum (MIN), emphasized frequency (ENF), and frequency bandwidth (BAND = MAX - MIN) were measured. Log-transformed frequencies and body mass data were subjected to a comparative analysis of independent contrast, using Goodwin's (1983) phylogeny. We show the existence of a negative relationship among frequencies and body mass, irrespective of the model of character evolution chosen. Similar results were obtained in raw contrast comparisons among 13 pairs of closely related species. Residuals of variation in song frequencies, after control for the effect of body mass and phylogeny, differed among habitats. In particular, closed habitat species use significantly higher MAX than their more open habitat relatives. This pattern contrasts with the one reported in studies based on community-wide comparisons, which in general do not correct song data for phylogeny and body mass, or include oscine species.
TL;DR: This paper conducted point counts of diurnal raptors on Boulder, Colorado, grasslands for three winters and summers, and compared results to landscape features of the count areas, finding that the first three species were more abundant on plots that included significant amounts of urban habitat, with a critical landscape threshold at about 5-7% urbanization: Bald Eagle (Haliaeetus leucocephalus), Ferruginous Hawk (Buteo regalis), Rough-legged Hawk, and Prairie Falcon (Falco mexicanus).
Abstract: We conducted point counts of diurnal raptors on Boulder, Colorado, grasslands for three winters and summers, and compared results to landscape features of the count areas. Four wintering species were scarce on plots that included significant amounts of urban habitat, with a critical landscape threshold at about 5-7% urbanization: Bald Eagle (Haliaeetus leucocephalus), Ferruginous Hawk (Buteo regalis), Rough-legged Hawk (B. lagopus), and Prairie Falcon (Falco mexicanus). Counts of the first three species also were positively correlated with proximity of the count plots to the nearest colony of black-tailed prairie dogs (Cynomys ludovicianus). Two breeding species, the Red-tailed Hawk (B. jamaicensis) and Swainson's Hawk (B. swainsoni), were more abundant on plots dominated by lowland hayfields and tallgrass prairies, as opposed to upland mixed and shortgrass prairies. They, along with the ubiquitous American Kestrel (Falco sparverius), were not sensitive to the amounts of urbanization (up to 30%) that occurred in the landscapes sampled. Results of this study suggest that urban open space grasslands can support sizable populations of most diurnal raptors, as long as prey populations persist, but that some species are highly sensitive to landscape urbanization.
TL;DR: The relationship between competitive foraging ability and age-specific mortality was examined in a free-ranging Rock Dove population and it was suggested that differential mortality of juvenile and adult pigeons could in pail arise from differences in competitive abilities over food.
Abstract: The general-stated view that high mortality rates in young birds arises from a lack of behavioral proficiency is based on limited empirical evidence. The relationship between competitive foraging ability and age-specific mortality was examined in a free-ranging Rock Dove (Columba livia) population. In this system, competition for food was intense and predators were scarce. Young and adult pigeons showed considerable niche overlap, were members in the same flocks, and used similar foraging techniques, all of which favored competition between these age groups. Competition was especially intense when pigeons foraged on food provided by the public, which was the preferred and major food source for the population. Young pigeons were poorer competitors than adults in all situations analyzed. First, juveniles foraged less rapidly, and so were more vulnerable to exploitation competition. Second, juveniles were subordinate to adults within a despotic social system, and so suffered more from contest competition. These findings suggest that juveniles were less likely to attain a positive energy balance through the day and were more vulnerable to starvation and disease. As predicted, more juvenile corpses than expected were found during the study, indicating that young pigeons experienced higher mortality rates than adults. It is therefore suggested that differential mortality of juvenile and adult pigeons could in pail arise from differences in competitive abilities over food.
TL;DR: It is concluded that the selection of woodrats provided a potential energetic benefit over the use of other prey, which provides a partial explanation for the owl's affinity for late seral forests.
Abstract: We tested three predictions of a hypothesis that states Northern Spotted Owls (Strix occidentalis caurina) select habitat according to the distribution of their primary prey. Our predictions were that Northern Spotted Owls should (1) select larger (> 100 g) species among the assemblage of available prey, (2) select habitats according to the distribution of large prey, and (3) the owl's reproductive success should be influenced by the availability of large prey. We also evaluated the potential energetic value of several prey species. We found that Northern Spotted Owls (n = 11 pairs and 1 single male) in northwestern California differentially selected the dusky-footed woodrat (Neotoma fuscipes), a moderately large sigmodontine rodent (x mass = 232 g). When foraging, owls selected late seral forest edge sites where dusky-footed woodrats were more abundant. Although the relationship between site selection, prey abundance, and the owl's breeding success was not statistically significant, the average abundance of dusky-footed woodrats at sites foraged by breeding owls (x = 11.4 woodrats 100-trap-nights -1 ) was greater than at sites foraged by nonbreeding owls (x = 4.7 woodrats 100-trap-nights -1 ). We estimated that a male Spotted Owl would require 150,015 to 336,232 kJ over a 153-day period while helping to produce one young, and concluded that the selection of woodrats provided a potential energetic benefit over the use of other prey. These findings provide a partial explanation for the owl's affinity for late seral forests.
TL;DR: It is demonstrated that social and biological factors can influence tolerance to intrusion, and intrusion-induced behaviors such as nest abandonment and decreased nest attentiveness have led to reduced reproduction and survival in species that are intolerant of intrusion.
Abstract: Human intrusion can be a serious problem for birds because it can cause displacement, prevent access to resources, and reduce reproduction and survival. The factors that influence avian tolerance to intrusion are poorly understood. We studied passerine responses to intrusion in Wyoming montane forests during the breeding season by using two indices of intrusion tolerance: detectability period, the amount of time that a bird remains near its initial flush point; and approach distance, how close one can get to a bird before it flushes. A solitary observer experimentally approached focal individuals and recorded detectability period, approach distance, the seasonal and daily timing of intrusion, number of nearby conspecifics, number of nearby heterospecific individuals, and surrounding vegetation conditions. Using data from the literature, we also assessed influences of migratory status, body mass, conspicuousness, and height above the ground at which species are active during the breeding season. Detectability period was significantly shorter, indicating intrusion tolerance was lower, when fewer conspecifics were nearby. Approach distance was significantly longer, indicating tolerance was lower, for more-conspicuous species and for species that are active closer to the ground. Effects of other variables studied were not significant. These results demonstrate that social and biological factors can influence tolerance to intrusion. Intrusion-induced behaviors such as nest abandonment and decreased nest attentiveness have led to reduced reproduction and survival in species that are intolerant of intrusion. With knowledge of factors that influence tolerance, the risk of disturbing birds that are sensitive to intrusion could be reduced.
TL;DR: Diet estimates of the contribution of terrestrial prey to the diet of Glaucous Gulls was less than what may be inferred from conventional methods of diet analysis, which emphasizes the benefit of combining stable-isotope and conventional analyses to infer temporal and geographic changes in diet of wild birds and other organism.
Abstract: We collected boluses and food remains of adult Glaucous Gulls (Larus hyperboreus) at or near nests and chicks, and digestive tracts from adults at three sites on the Yukon-Kuskokwim Delta, Alaska that differed in proximity to marine and terrestrial foods. We observed both geographic and temporal variation in diet; gulls consumed proportionately more terrestrial prey after peak hatch in late June, and gulls near the coast consumed proportionately more marine prey than gulls at two inland areas. Goslings occurred in > 60% of all samples from these inland areas. We compared these data to those from a previous study in western Alaska and found no marked differences. Evidence for similar patterns of geographic and temporal variation in diet was found using measurements of stable-carbon and nitrogen isotopes in gull and prey tissues. Stable isotope analysis further revealed that adult gulls consumed proportionately more marine prey (saffron cod, Eleginus gracilis) than they fed to their young. Using isotopic models, we estimated that 7-22% and 10-23% of the diet of adult and juvenile Glaucous Gulls, respectively, was comprised of terrestrial species. In addition to significant age-related variation, dietary estimates varied among geographic areas and between pre- and post-hatch periods. Overall, our isotopic estimates of the contribution of terrestrial prey to the diet of Glaucous Gulls was less than what may be inferred from conventional methods of diet analysis. Our study emphasizes the benefit of combining stable-isotope and conventional analyses to infer temporal and geographic changes in diet of wild birds and other organism.
TL;DR: This paper tracked four male Magellanic Penguins (Spheniscus magellanicus) from the beginning of their winter migration for periods ranging from three to six weeks and found that the birds traveled northeast along the coast at speeds consistent with sighting and band-return data which suggest a round-trip winter migration in this species of up to several thousand kilometers.
Abstract: We tracked four male Magellanic Penguins (Spheniscus magellanicus) from the beginning of their winter migration for periods ranging from three to six weeks. Upon leaving the colony at Punta Tombo, Argentina where they had bred and molted, all four birds traveled northeast along the coast at speeds consistent with sighting and band-return data which suggest a round-trip winter migration in this species of up to several thousand kilometers. Three of the birds followed a similar route, moved at approximalely the same rate, and were still moving northeastward at a distance of over 800 km from the colony when signals ceased. The fourth bird departed from the northeast route at approximately 300 km into its trip and remained in a large bay for at least 29 days, when the last signal was received. Initially, the birds traveled rapidly and made few deep dives. Later, their rate of travel slowed, their paths became more erratic, and they made more deep dives, all indications of probable foraging. This suggests that location of the penguin migration route and rate of travel along it may be determined by seasonal movement of prey. As all birds were within 250 km of shore for the entire period in which signals were received, our results underscore the importance of controlling pollution associated with petroleum transport along the coast of Argentina, currently a major source of Magellanic Penguin mortality.
TL;DR: The results suggest that growth and survival of Roseate Tern chicks are determined primarily by parental quality; much of the information about parental quality is expressed by the time the eggs are laid, and most of it is expressed during the first 3 days old.
Abstract: We measured growth of Roseate Tern (Sterna dougallii) chicks at a colony in Connecticut in 10 successive years, 1987-1996. Data on body mass during the first 3-4 days of life were fitted to a quadratic regression model, yielding three parameters of early growth for each of 1,551 chicks: mass at hatching, linear growth, and quadratic growth. First chicks in each brood (A-chicks) exceeded second chicks (B-chicks) in each of the three growth parameters; A-chicks from broods of two grew faster during the first 3 days than single chicks. The three parameters of early growth depended upon egg mass, hatch order, hatch date, and year, but not on parental age after controlling for effects of the other vari- ables. The linear and quadratic growth parameters were negatively correlated. Subsequent growth and survival of chicks were predicted by all three parameters of early growth. After controlling for effects of early growth, none of the other variables measured (hatch date, egg mass, parental age, hatching asynchrony, female-female pairing, or trapping) contributed significantly to explaining later growth or survival. Year effects were substantial in only 2 of the 10 years of study. Individual pairs were consistent in performance (as indexed by early growth) in successive years. These results suggest that growth and survival of Roseate Tern chicks are determined primarily by parental quality; much of the information about parental quality is expressed by the time the eggs are laid, and most of it is expressed by the time the chicks are three days old.
TL;DR: It is concluded that Bell Miners do not mate promiscuously and that the majority of helpers are close relatives of the breeding pair, which seems to have evolved as a system of collateral kinship among the breeding birds and helpers.
Abstract: We used multi-locus DNA fingerprinting to determine the parentage of 13 broods of Bell Miner (Manorina melanophrys) nestlings. Despite very large contingents of male helpers attending individual nests and living in close proximity to breeding females, we found only one instance of extra-pair paternity in 24 nestlings. The genetic father of the extra-pair nestling was not among the males in our study population. The majority of helpers (67% of 52 cases) were close relatives (r > 0.25) of at least one parent of the brood being provisioned. Helpers were more often closely related to the male than the female parent. Only 17% of cases involved helpers that were apparently unrelated to either of the parents of the broods being aided. We conclude that Bell Miners do not mate promiscuously and that the majority of helpers are close relatives of the breeding pair. Cooperative breeding in Bell Miners seems to have evolved as a system of collateral kinship among the breeding birds and helpers.
TL;DR: It is concluded that future studies should consider age as a major source of variability in avian plasma chemistry, and that results obtained from captivity should be used cautiously to interpret plasma chemistry in the study and rehabilitation of wild birds.
Abstract: Despite the interest in blood chemistry for studying ecological and pathological characteristics of birds, sources of variability such as age and captivity are poorly understood, and reference values usually are obtained from adult captive birds. We determined 15 plasma chemical variables for 164 free-living Egyptian Vultures (Neophron percnopterus) of three age groups (nestlings, subadults, and adults), and for 9 captive adults. Free-living subadults and adults exhibited identical plasma chemistry values. Nestlings had significantly higher levels of creatinine, urate, urea, triglycerides, calcium, phosphorus, and alkaline phosphatase (AP) than both free-living subadults and adults, but lower values of glucose and aspartate aminotransferase (AST). Captive adults had significantly higher levels of total protein, albumin, creatinine, urate, cholesterol, calcium, phosphorus, and AST than free-living adults, which we attribute to differences in diet quality and physical activity. We conclude that future studies should consider age as a major source of variability in avian plasma chemistry, and that results obtained from captivity should be used cautiously to interpret plasma chemistry in the study and rehabilitation of wild birds.
TL;DR: Because cowbird parasitism appears to impose substantial costs on Indigo Bunting nestlings and adults, concern over the conservation implications of parasitism should not be limited to species that suffer total reproductive failure when parasitized.
Abstract: Brood parasitism by Brown-headed Cowbirds (Molothrus ater) is known to affect the fitness of many hosts by causing a reduction in the number of chicks that fledge from parasitized nests However, little is known ahout less immediate effects on host fitness We studied nestling growth and food acquisition and parental provisioning in parasitizcd and unparasitized nests of the Indigo Bunting (Passerina cyanea) Indigo Bunting nestlings in parasitized nests exhibited reduced rates of mass gain, but not tarsus growth, relative to bunting chicks in unparasitized nests Bunting nestlings in parasitized nests received less food than did buntings in unparasitized nests Buntings in parasitized nests spent more time begging than did those in unparasitized nests, but energy expended in this behavior may not have detracted greatly from the amount of energy available for growth Adults at parasitized nests exhibited a higher provisioning rate than those at unparasitized nests Increascd provisioning by adult buntings at parasitized nests did not come at the expense of time spent brooding nestlings, but increased provisioning has the potential to affect the survival and future reproductive success of host adults Because cowbird parasitism appears to impose substantial costs on Indigo Bunting nestlings and adults, concern over the conservation implications of parasitism should not be limited to species that suffer total reproductive failure when parasitized
TL;DR: The phylogeny suggests a series of adaptive shifts from the ancestral habitat of scrub and river margins in tropical lowlands to bushy highlands and elfin forest, then colonization of edge habitats in the humid montane forest, and finally interior montane and submontane forest.
Abstract: Most species of chat-tyrants (Ochthoeca, Silvicultrix) are widespread along the length of the Andes, with broadly overlapping ranges, but segregated in different altitudinal zones or habitats. We used mitochondrial DNA sequences to study their phylogenetic relationships. Our data show considerable divergence and multiple base substitutions at some positions between geographically overlapping species. Such divergence probably predates the period of marked ecoclimatic changes in the Pleistocene, whereas vicariance patterns may reflect events in the lower Pleistocene. Only some of the boundaries between allospecies correspond to marked topographic barriers, and we suggest that sharp species-replacements indicate secondary contact zones. An evolutionary dynamic scenario is suggested where divergence of isolated populations is followed by establishment of sharp geographical replacements and, with development of full ecological compatibility, establishment of broad overlap along the Andes cordillera. The phylogeny suggests a series of adaptive shifts from the ancestral habitat of scrub and river margins in tropical lowlands to bushy highlands and elfin forest, then colonization of edge habitats in the humid montane forest, and finally interior montane and submontane forest. However, the adaptive redistribution has obscured the early vicariance events in the group. The results support the monophyly of all chat-tyrants, but with a distinctive internal structure, where Silvicultrix is a monophyletic internal branch within Ochthoeca. Support also is given for a close relationship between Tumbezia salvini and Ochthoeca. We suggest keeping Tumbezia as a separate genus, merging Silvicultrix with Ochthoeca, and elevating O. frontalis and spodionota, and O. cinnamomeiventris and thoracica to species rank.
TL;DR: It is concluded that abdominal implantations alter murre nesting behavior.
Abstract: We implanted 6 Common Murres (Uria aalge) and 10 Thick-billed Murres (Uria lomvia) with satellite transmitters and compared subsequent presence at the colony, nesting status, and provisioning to a control group that underwent a simple surgical procedure. In the 10 days following implantation, we resighted 10 of 11 control birds at the colony and 6 of 16 implanted birds. Of the birds that returned, 7 of 10 control birds retained breeding status, whereas zero of six implanted birds retained breeding status. We conclude that abdominal implantations alter murre nesting behavior.
TL;DR: Song Sparrow nest-site selection varied among forest types, but lateral cover at ground level and foliage cover above the nest were similar for nests in each forest type, suggesting that foliage coverabove the nest may increase parasitism.
Abstract: We studied Song Sparrow (Melospiza melodia) reproductive ecology in natural and restored riparian forest to evaluate the influence of habitat structure and nest-site selection on parasitism by Brown-headed Cowbirds (Molothrus ater). Logistic regression revealed that habitat structure affected the probability of parasitism at two scales, BROAD (within 11.3 m of the nest) and LOCAL (within 5 m of the nest). Nests with abundant lateral cover at a height of < I m (BROAD) were less likely to be parasitized, suggesting that lateral cover at ground level may reduce parasitism by concealing host movements in the vicinity of the nest. In contrast, nests with abundant foliage cover at a height of 2-3 m (LOCAL) were more likely to be parasitized, suggesting that foliage cover above the nest may increase parasitism by providing perches from which female cowbirds can watch host activities and find nests. Sparrow nest-site selection varied among forest types, but lateral cover at ground level and foliage cover above the nest were similar for nests in each forest type. Results suggest that further research on the effects of habitat structure on nest-site selection and cowbird parasitism could lead to methods of reducing parasitism through appropriate habitat management and restoration efforts.
TL;DR: Diurnal time-activity budgets on American Avocets, Long-billed Dowitchers, Least Sandpiper, and Western Sandpipers found each species use different behavioral strategies in response to such factors as migration distances, energetic needs, differential predation, and diet.
Abstract: Playas in the Southern High Plains (SHP) are important for migrant shorebirds, but the functional role of playas to migrant shorebirds is not clearly understood. We conducted diurnal time-activity budgets on American Avocets (Recurvirostra americana), Long-billed Dowitchers (Limnodromus scolopaieus), Least Sandpipers (Calidris minutilla), and Western Sandpipers (C. mauri) in spring and fall 1993 and 1994 in 69 playas on the SHP of Texas. During both seasons, Least and Western Sandpipers spent 70-80% of their time feeding. Long-billed Dowitchers spent 77% of their time feeding in spring, but spent more time sleeping and less feeding in fall. American Avocets spent 41-50% of their time feeding and 34-40% of their time sleeping during each season. All four species spent minimal time engaged in locomotion, body maintenance, alert, and aggressive behaviors. American Avocets and Long-billed Dowitchers fed most during the midday and late periods and slept most during the early period. Least Sandpipers fed most during the early period, whereas feeding activities of Western Sandpipers remained 70-80% throughout the day. Each of these species use different behavioral strategies in response to such factors as migration distances, energetic needs, differential predation. nocturnal foraging, and diet. Playas appear to serve as important intermediate stopover sites for shorebirds during migration.
TL;DR: Although both Roseate and Sandwich Terns in Puerto Rico fed primarily on the same few species of fish, they did so in different proportions, which is consistent with an earlier study demonstrating foraging habitat segregation in these two species.
Abstract: I analyzed regurgitations from adult Roseate Terns (Sterna dougallii) and Sandwich Terns (S. sandvicensis) breeding in southwestern Puerto Rico in 1992 and 1993, and compared them with observations of prey delivered to chicks from 1991 to 1993 to determine similarities in the prey base for the two tern species during different stages in the breeding cycle, and differences between the diets of adults and chicks. I sampled prey fish at Turrumote lagoon where terns regularly fished to determine if the species composition of the fishes in the lagoon was representative of the prey base taken by terns. Adult Roseate Terns fed primarily on dwarf herrings (Jenkinsia lamprotaenia) and anchovies (Anchoa spp.), and fed chicks mostly dwarf herrings and sardines (Harengula and Opisthonema spp.); few anchovies were fed to chicks. Adult Sandwich Terns fed primarily on silversides (HypOatherina harringtonensis) and sardines, and fed chicks mostly sardines and dwarf herrings; few silversides were fed to chicks. In 1992, both tern species apparently compensated for a lack of sardines by feeding their chicks proportionally more dwarf herrings. Diet diversity was greater for Sandwich than for Roseate Terns both in regurgitations and in prey delivered to chicks. Dietary overlap between the two species was low prior to, but converged following, chick hatching. Both species fed chicks increasingly larger prey as the chicks grew larger, but patterns were not consistent among years. Prey samples taken from Turrumote lagoon were representative of, but not in proportion to, the species of prey fed to chicks. These results indicate that although both Roseate and Sandwich Terns in Puerto Rico fed primarily on the same few species of fish, they did so in different proportions. This finding is consistent with an earlier study demonstrating foraging habitat segregation in these two species.
TL;DR: Redhead females exhibited one of the lowest incubation constancy among duck species (Anatidae), coupled with a comparatively high number of incubation recesses per day, and was higher for older females and for females of lower body mass and was lower on days with higher maximum daily temperatures.
Abstract: Incubation constancy, i.e., the proportion of time on the nest, of female Red-heads (Aythya americana) was examined during the summers of 1995 and 1996 in relation to female age, body mass, and ambient conditions. Redhead females exhibited one of the lowest incubation constancy (82%) among duck species (Anatidae), coupled with a comparatively high number of incubation recesses per day. Low constancy was not due to excessive disturbance at the nest or reduced maternal investment in the clutch, but was probably related to energetic constraints of the female imposed by laying parasitic eggs prior to nesting. As in most other duck species, incubation constancy decreased over the incubation period. Age, mass, and maximum daily temperature, and the interactions of initiation day X age and mass X date significantly influenced daily incubation constancy. Constancy was higher for older females and for females of lower body mass and was lower on days with higher maximum daily temperatures.
TL;DR: In addition, extreme variability in wetland habitat conditions present special problems for conducting censuses of species inhabiting these areas as mentioned in this paper, and they examined these issues in assessing multi-scale shorebird (order: Charadriiformes) censuses conducted in the western Great Basin from 1992-1997.
Abstract: Broad-scale avian surveys have been attempted within North America with mixed results. Arid regions, such as the Great Basin, are often poorly sampled because of the vastness of the region, inaccessibility of sites, and few ornithologists. In addition, extreme variability in wetland habitat conditions present special problems for conducting censuses of species inhabiting these areas. We examined these issues in assessing multi-scale shorebird (order: Charadriiformes) censuses conducted in the western Great Basin from 1992-1997. On ground surveys, we recorded 31 species of shorebirds, but were unable to accurately estimate population size. Conversely, on aerial surveys we were able to estimate regional abundance of some shorebirds, but were unable to determine species diversity. Aerial surveys of three large alkali lakes in Oregon (Goose, Summer, and Abert Lakes) revealed > 300,000 shorebirds in one year of this study, of which 67% were American Avocets (Recurvirostra americana) and 30% phalaropes (Phalaropus spp.). These lakes clearly meet Western Hemisphere Shorebird Reserve Network guidelines for designation as important shorebird sites. Based upon simulations of our monitoring effort and the magnitude and variation of numbers of American Avocets, detection of 5-10% negative declines in populations of these birds would take a minimum of 7-23 years of comparable effort. We conclude that a combination of ground and aerial surveys must be conducted at multiple sites and years and over a large region to obtain an accurate picture of the diversity, abundance, and trends of shorebirds in the western Great Basin.