Stopover biology of migratory landbirds in a heavily urbanized landscape, the New York metropolitan area

Migration routes of many Nearctic-Neotropical landbirds pass through the most urbanized regions of North America. Migrants use urban habitat fragments as stopover sites and commonly occur in cities at exceptional density. Yet, knowledge of migrant stopover biology and refueling opportunities in such places is severely limited. This dissertation examined several aspects of migrant stopover biology in the New York metropolitan area to gain a more holistic understanding of how migratory landbirds utilize urban stopover sites, and ultimately to assess the quality of urban habitats as stopover sites. I first generated morphometric predictive models using salvaged bird specimens to allow me in subsequent studies to noninvasively measure the energetic condition (fat mass) of migrants in New York City (NYC). Next I compared the refueling performance of migrants in NYC to that of conspecifics in less-disturbed forests outside of the city. Blood plasma metabolite profiles indicated that refueling conditions for migrants were no poorer in NYC than in the non-urban habitats. Further, migrant refueling rates were comparable to, and in some cases higher than, those reported in the literature for birds at various non-urban stopover sites. Measures of arthropod biomass suggested food abundance for insectivorous migrants was also similar within and outside NYC. I then showed that stopover refueling in NYC often involved substantial increases in lean mass. This finding carries implications for stopover habitat management practices, as migrants using these sites will require high-protein foods in addition to the lipid- and carbohydrate-rich foods that maximize fattening rates. Next, radio-telemetry data from a small pilot study provided one of the first descriptions of migrant stopover durations within a city. Stopover durations ranged 1-14 days and were negatively related to fat mass, but not lean body mass, upon arrival. A larger-scale telemetry study revealed that migrant spatial behaviour in NYC was in many ways similar to what has been observed in passerine migrants in non-urban areas. Movement patterns were indicative of an ability to search for, locate, and occupy suitable microhabitat, and temporary home ranges suggested forest size was more than sufficient to meet their area requirements. Collectively, these studies provide a comprehensive assessment of the quality of urban habitats as migratory bird stopover sites. Findings indicated that the sites examined are functioning in the same fashion as less-disturbed, larger forest tracts elsewhere. No evidence was found to suggest that stopover refueling conditions within one of the world’s most urbanized landscapes are inadequate for migrating landbirds

Mobilization of mercury from lean tissues during simulated migratory fasting in a model songbird

The pollutant methylmercury accumulates within lean tissues of birds and other animals. Migrating birds catabolize substantial amounts of lean tissue during flight which may mobilize methylmercury and increase circulating levels of this neurotoxin. As a model for a migrating songbird, we fasted zebra finches (Taeniopygia guttata) that had been dosed with 0.0, 0.1, and 0.6 parts per million (ppm) dietary methylmercury and measured changes in blood total mercury concentrations (THg) in relation to reductions in lean mass. Birds lost 6-16% of their lean mass during the fast, and THg increased an average of 12% and 11% in the 0.1 and 0.6 ppm treatments, respectively. Trace amounts of THg in the 0.0 ppm control group also increased as a result of fasting, but remained extremely low. THg increased 0.4 ppm for each gram of lean mass catabolized in the higher dose birds. Our findings indicate that methylmercury is mobilized from lean tissues during protein catabolism and results in acute increases in circulating concentrations. This is a previously undocumented potential threat to wild migratory birds, which may experience greater surges in circulating methylmercury than demonstrated here as a result of their greater reductions in lean mass

Conservation Status and Monitoring of Bicknell\u27s Thrush in the Adirondacks and New England: A Brief Review

Bicknell’s thrush is among the most rare and probably most threatened species in North America and is considered the Nearctic-Neotropical migrant of highest conservation priority in the Northeast. The species breeds in high elevation spruce-fir forests in the northeastern US and Canada and is adapted to naturally disturbed habitats impacted by montane processes such as wind throw and fir waves. The U.S. Fish and Wildlife Service has recently issued a finding that the Bicknell’s thrush may warrant listing as threatened or endangered under the Endangered Species Act. The challenges facing Bicknell’s thrush are many, and New York State has a significant role to play in helping to safeguard the future of the species in the region. We provide a brief summary of regional monitoring and research efforts, what has been learned from them, and suggestions that may enhance the conservation of the species here and elsewhere

Quantitative magnetic resonance analysis and a morphometric predictive model reveal lean body mass changes in migrating Nearctic-Neotropical passerines

Abstract Most studies of lean mass dynamics in freeliving passerine birds have focused on Old World species at geographical barriers where they are challenged to make the longest non-stop flight of their migration. We examined lean mass variation in New World passerines in an area where the distribution of stopover habitat does not require flights to exceed more than a few hours and most migrants stop flying well before fat stores near exhaustion. We used either quantitative magnetic resonance (QMR) analysis or a morphometric model to measure or estimate, respectively, the fat and lean body mass of migrants during stopovers in New York, USA. With these data, we examined (1) variance in total body mass explained by lean body mass, (2) hourly rates of fat and lean body mass change in singlecapture birds, and (3) net changes in fat and lean mass in recaptured birds. Lean mass contributed to 50% of the variation in total body mass among white-throated sparrows Zonotrichia albicollis and hermit thrushes Catharus guttatus. Lean mass of refueling gray catbirds Dumetella carolinensis and white-throated sparrows, respectively, increased 1.123 and 0.320 g h -1 . Lean mass of ovenbirds Seiurus aurocapillus accounted for an estimated 33-40% of hourly gains in total body mass. On average 35% of the total mass gained among recaptured birds was lean mass. Substantial changes in passerine lean mass are not limited to times when birds are forced to make long, non-stop flights across barriers. Protein usage during migration is common across broad taxonomic groups, migration systems, and migration strategies

Passerine migrant stopover duration and spatial behaviour at an urban stopover site

a b s t r a c t Migration routes of many NearcticeNeotropical landbirds pass through the most urbanized regions of North America. Migrants are known to use urban habitats as stopover sites and often occur in cities at exceptional density; yet knowledge of migrant behaviour and ecology in such places is surprisingly limited. We radio-tracked ovenbirds (Seiurus aurocapillus) during stopovers in a New York City park to obtain some of the first detailed information on how landbird migrants utilize an urban habitat as a stopover site. We examined fine-scale movement patterns, home range sizes, stopover durations, and how arrival condition affected each of these metrics. During both seasons, most birds moved widely throughout the site upon presumed arrival and then either continued migration that night or settled into a more defined area on subsequent days. Area usage varied markedly among individuals during both seasons, ranging 1e16 ha. Stopover durations averaged 3.0 days (range ¼ 1e10 days) during spring and 2.9 days (range ¼ 1e14 days) during autumn. Spatial behaviours and stopover durations were not influenced by arrival condition during spring, and during autumn only movement rates and displacement distances were significantly (negatively) condition-related. Our findings do not support previous assumptions that urban stopover habitats are only used by migrants briefly in times of urgency when alternatives are unavailable. At least half of the birds we studied stopped over for multiple days during both seasons, and bird movements were indicative of an ability to search for, locate, and occupy suitable micro-sites. Ovenbird behaviour in our study site was similar in many ways to what has been observed in recent telemetry studies of ovenbirds and other passerine migrants at various non-urban stopover sites

Quantitative meta‐analysis reveals no association between mercury contamination and body condition in birds

Mercury contamination is a major threat to the global environment, and is still increasing in some regions despite international regulations. The methylated form of mercury is hazardous to biota, yet its sublethal effects are difficult to detect in wildlife. Body condition can vary in response to stressors, but previous studies have shown mixed effects of mercury on body condition in wildlife. Using birds as study organisms, we provide the first quantitative synthesis of the effect of mercury on body condition in animals. In addition, we explored the influence of intrinsic, extrinsic and methodological factors potentially explaining cross-study heterogeneity in results. We considered experimental and correlative studies carried out in adult birds and chicks, and mercury exposure inferred from blood and feathers. Most experimental investigations (90%) showed a significant relationship between mercury concentrations and body condition. Experimental exposure to mercury disrupted nutrient (fat) metabolism, metabolic rates, and food intake, resulting in either positive or negative associations with body condition. Correlative studies also showed either positive or negative associations, of which only 14% were statistically significant. Therefore, the overall effect of mercury concentrations on body condition was null in both experimental (estimate ± SE = 0.262 ± 0.309, 20 effect sizes, five species) and correlative studies (-0.011 ± 0.020, 315 effect sizes, 145 species). The single and interactive effects of age class and tissue type were accounted for in meta-analytic models of the correlative data set, since chicks and adults, as well as blood and feathers, are known to behave differently in terms of mercury accumulation and health effects. Of the 15 moderators tested, only wintering status explained cross-study heterogeneity in the correlative data set: free-ranging wintering birds were more likely to show a negative association between mercury and body condition. However, wintering effect sizes were limited to passerines, further studies should thus confirm this trend in other taxa. Collectively, our results suggest that (i) effects of mercury on body condition are weak and mostly detectable under controlled conditions, and (ii) body condition indices are unreliable indicators of mercury sublethal effects in the wild. Food availability, feeding rates and other sources of variation that are challenging to quantify likely confound the association between mercury and body condition in natura. Future studies could explore the metabolic effects of mercury further using designs that allow for the estimation and/or manipulation of food intake in both wild and captive birds, especially in under-represented life-history stages such as migration and overwintering