How to capture wild passerine species to study baseline corticosterone levels

Baseline corticosterone levels have been suggested to be an effective tool to assess and monitor the health status of individuals and populations of wild birds. However, measuring baseline corticosterone levels in the field is difficult because the capture protocol may affect rates of corticosterone secretion. In passerine birds, two methods of capture are widely used: (1) passive netting consisting of monitoring mist-nets frequently to check if a bird has been caught; and (2) target netting consisting of installing a conspecific decoy and/or playing a tape-recorded conspecific song in the vicinity of a mist-net until the territorial bird is captured. Our objective here was to determine whether these methods of capture are effective at achieving non-disturbed baseline corticosterone levels in American Redstarts (Setophaga ruticilla). We found that passive netting was associated with elevated corticosterone levels, suggesting that hanging in a net for several minutes activates the HPA axis and, thus, elicits an adreno-cortical stress response. In contrast, target netting was not associated with an increase in corticosterone levels, regardless of the length of time between when the target bird first approached the net and when it was captured. Therefore, we suggest that researchers interested in estimated baseline corticosterone in this species use target netting and not passive netting

Responses of river-dependent wildlife to dam removal, salmon restoration, and nutrient subsidies in the Elwha River Watershed, Olympic Peninsula, Washington

The ongoing removal of two hydroelectric dams from the Elwha River on Washington’s Olympic Peninsula provides an unprecedented opportunity to study the effects of dam removal and subsequent salmon restoration on river-dependent wildlife species. Salmon are widely known to distribute marine nutrients into freshwater systems, providing benefits to both riverine and upland wildlife communities through improved nutrient availability. We examined two species of river-dependent wildlife (river otter Lontra canadensis, and American dipper Cinclus mexicanus) to gather data on home range and seasonal movement patterns, body condition, and dietary contributions from marine-derived nutrients prior to and during dam removal. We radio-tracked ten river otters in the Elwha River and adjacent Salish Sea, and collected biological samples from all otters captured in the Elwha River as well as 246 dippers captured across four watersheds with varying qualities of salmon runs. We are using stable isotopes (C, N) to track marine derived nutrient contributions to the diets of otters and dippers, species that are both sensitive indicators of aquatic food web quality. In both species, stable-isotope ratios were more enriched in tissues from areas with intact salmon migrations, indicating greater consumption of salmon tissues and potential enrichment of invertebrate prey. In dippers, females breeding in areas with salmon migrations were in better condition and both sexes were more likely to occupy territories in fall. Adult condition patterns were more pronounced behind anthropogenic, compared to natural, obstructions. These patterns indicate that dams have sizeable individual level impacts on aquatic consumers and provide a valuable baseline to track the recovery of this watershed following completion of dam removal

Incorporating site and year-specific deuterium ratios (H-2) from precipitation into geographic assignments of a migratory bird

The study of migratory connectivity is rapidly growing in ornithology, as is the technology used to measure it. While use of extrinsic markers, such as archival tags, is becoming more prevalent, for many small species the best tool available for tracking birds remains intrinsic markers, such as stable-hydrogen isotope ratios (H-2). Many researchers have raised concerns that spatial and temporal environmental variation introduces a large amount of error into isotope-based assignments, limiting their utility. Here, using feathers, we sought to address these issues in developing H-2 base maps for assigning pied flycatchers Ficedula hypoleuca of known origin to 15 sites across the breeding range (approx. 4 020 800 km(2)). We evaluated the effects of including random site variation and year-specific precipitation H-2 (H-2(P)) maps on assignments, compared to using mean annual growing season H-2(p) and no site effects. We found a positive correlation between feather H-2 (H-2(F)) and mean annual H-2(P,) resulting from large scale geographic variation. Repeatability of feather H-2 for individuals sampled in multiple years was strong overall, but variable among populations. Annual variation in H-2(P) explained 21% of within individual variation in H-2(F). Neither year- nor site-specific methods improved assignment precision or accuracy. All three methods assigned flycatchers of unknown origin captured at an African overwintering site to similar breeding areas. However, methods using long-term means of H-2(p) assigned birds more precisely than year-specific methods. Our results suggest that annual variation in this system is primarily a result of food web or individual level processes and that random site effects are not strong enough to drastically impact accuracy. We conclude that improvements in isotope based geographic assignments will rely on the addition of prior information, such as relative abundance in a Bayesian framework, or additional intrinsic markers

Prealternate molt-migration in Rusty Blackbirds and its implications for stopover biology

To achieve greater understanding of the full annual cycles of birds, it is critical to describe the spatial nature of little-understood phases. One of the least understood aspects of avian annual cycles is the ecology of molt: the periodic replacement of feathers. While work on the spatial nature of molt in migratory passerines has increasingly found incidences of species and populations completing molt during migration, this work has been limited entirely to prebasic flight feather molt. We examined the prevalence and progression of contour feather molt in a migratory songbird, the Rusty Blackbird (Euphagus carolinus), during spring stopover. We found that 98% of birds exhibited a partial prealternate molt during stopover, primarily in the head region. Furthermore, molt intensity peaked in the middle of the migration period and was negatively associated with fat score. This is the first evidence in the passerine literature of an obligate prealternate molt completed during migration, which is in many ways similar to the molt strategy of a variety of shorebirds (Families Charadriidae and Scolopacidae). These findings could prove crucial to understanding the constraints on spring migration in this declining species. Furthermore, we argue that molt schedules such as those of the Rusty Blackbird and shorebirds should be referred to as “prealternate molt-migration,” broadening the traditional definition of molt-migration beyond prebasic flight feather molt

How to capture wild passerine species to study baseline corticosterone levels

Baseline corticosterone levels have been suggested to be an effective tool to assess and monitor the health status of individuals and populations of wild birds. However, measuring baseline corticosterone levels in the field is difficult because the capture protocol may affect rates of corticosterone secretion. In passerine birds, two methods of capture are widely used: (1) passive netting consisting of monitoring mist-nets frequently to check if a bird has been caught; and (2) target netting consisting of installing a conspecific decoy and/or playing a tape-recorded conspecific song in the vicinity of a mist-net until the territorial bird is captured. Our objective here was to determine whether these methods of capture are effective at achieving non-disturbed baseline corticosterone levels in American Redstarts (Setophaga ruticilla). We found that passive netting was associated with elevated corticosterone levels, suggesting that hanging in a net for several minutes activates the HPA axis and, thus, elicits an adreno-cortical stress response. In contrast, target netting was not associated with an increase in corticosterone levels, regardless of the length of time between when the target bird first approached the net and when it was captured. Therefore, we suggest that researchers interested in estimated baseline corticosterone in this species use target netting and not passive netting

Habitat Selection of Three Neotropical Grassland Birds Is Dependent on Vegetation Structure and Resources

Grassland birds are globally imperiled. Those of endemic Neotropical savannas may be particularly threatened as knowledge of the ecology of many species is lacking, restricting our ability to take decisive conservation action. During the dry (non-breeding) season of 2010, we studied the population size, distribution, and habitat associations of the Cock-tailed Tyrant (Alectrurus tricolor), Black-masked Finch (Coryphaspiza melanotis), and Wedge-tailed Grass-finch (Emberiziodes herbicola) across a disturbance-mediated savanna–grassland gradient in Beni, Bolivia. We used distance sampling and surveyed structural and resource-specific habitat features at plots where birds were present versus random locations. Occupancy models identified fine-scale habitat associations. Cock-tailed Tyrant (7.1 ind./km2) specialized on open habitats in areas expected to be heavily inundated in the wet season, avoided trees, and selected tall grassy swards. Black-masked Finch (25.1 ind./km2) occurred across the gradient, associating with tall, forb-rich swards, sparse shrubs, and low levels of fruiting and seeding vegetation. Wedge-tailed Grass-finch (27.9 ind./km2) also occurred across the gradient, particularly associated with tall, forb-rich swards, abundant seeding grasses, and sparse shrubs. Our results offer the first quantitative abundance estimates for these species in Beni, provide vital baselines for future monitoring, and improve knowledge of the ecology and conservation management needs of these species. Importantly, our results suggest that populations of these three grassland birds may be best maintained in heterogenous, mosaic landscapes that can be produced by carefully managed burning and grazing. Further research in the breeding season would facilitate making stronger, more specific management recommendations