An inexpensive, 3D‐printable breast muscle meter for field ornithologists

The size of the pectoral muscle is an important component of body condition in birds and has been linked to indices of fitness and migratory performance. Bauchinger et al. (2011. Journal of Ornithology 152: 507–514) developed, calibrated, and validated an aluminum “muscle meter” device that estimates the size of pectoral muscles noninvasively. To make this tool more widely available, we created a CAD model from 3D-scan data of the aluminum muscle meter that can be 3D-printed in durable plastic for ~ $30 USD. We tested this device on seven species of songbirds in Jamaica, The Bahamas, Cameroon, Equatorial Guinea, and Michigan. We demonstrate that the breast muscle meter measurements are (1) repeatable among users, (2) correlated with a four-category visual breast muscle scoring system, and (3) correlated with scaled mass index (an index of body condition). Muscle scores from our device outperformed the traditional four-category muscle scoring system in predicting scaled mass index. Finally, with our device, we quantified the increasing breast muscle size of American Redstarts (Setophaga ruticilla) from March through May as they prepared for spring migration. Given the precision of the 3D-scanning hardware used to generate our 3D image for printing, we produced a plastic muscle meter that is as precise and useful as the aluminum original, but more cost-effective and widely available

Differential migration and the link between winter latitude, timing of migration, and breeding in a songbird

Patterns of connectivity between breeding and wintering grounds can have important implications for individual fitness and population dynamics. Using light-level geolocators and stable hydrogen isotopes (delta H-2) in feathers, we evaluated differential migration of Savannah sparrows (Passerculus sandwichensis) breeding on Kent Island in the Bay of Fundy, New Brunswick, Canada in relation to sex, age, and body size. Based on geolocators recovered from 38 individuals between 2012 and 2014, the winter distribution was centered in North Carolina (median latitude 34A degrees, range 26A degrees-41A degrees), with males overwintering, on average, approximately 275 km further north than females. Based on analyses of tail feather samples collected from 106 individuals from the same population between 2008 and 2012, males and adults had more negative delta H-2 values than females and juveniles, respectively, providing additional evidence that males wintered north of females and that adults wintered north of juveniles. Winter latitude and delta H-2 values within each sex were not found to be related to body size. From geolocator data, males returned to the breeding grounds, on average, 14 days earlier than females. For males, there was some evidence that arrival date on the breeding grounds was negatively correlated with winter latitude and that individuals which arrived earlier tended to breed earlier. Thus, benefits for males of early arrival on the breeding grounds may have contributed to their wintering farther north than females. Social dominance may also have contributed to age and sex differences in winter latitude, whereby dominant males and adults forced subordinate females and juveniles further south

Atmospheric pressure predicts probability of departure for migratory songbirds

Abstract Background Weather can have both delayed and immediate impacts on animal populations, and species have evolved behavioral adaptions to respond to weather conditions. Weather has long been hypothesized to affect the timing and intensity of avian migration, and radar studies have demonstrated strong correlations between weather and broad-scale migration patterns. How weather affects individual decisions about the initiation of migratory flights, particularly at the beginning of migration, remains uncertain. Methods Here, we combine automated radio telemetry data from four species of songbirds collected at five breeding and wintering sites in North America with hourly weather data from a global weather model. We use these data to determine how wind profit, atmospheric pressure, precipitation, and cloud cover affect probability of departure from breeding and wintering sites. Results We found that the probability of departure was related to changes in atmospheric pressure, almost completely regardless of species, season, or location. Individuals were more likely to depart on nights when atmospheric pressure had been rising over the past 24 h, which is predictive of fair weather over the next several days. By contrast, wind profit, precipitation, and cloud cover were each only informative predictors of departure probability in a single species. Conclusions Our results suggest that individual birds actively use weather information to inform decision-making regarding the initiation of departure from the breeding and wintering grounds. We propose that birds likely choose which date to depart on migration in a hierarchical fashion with weather not influencing decision-making until after the departure window has already been narrowed down by other ultimate and proximate factors

DataSheet_1_Incorporating drivers of global change throughout the annual cycle in species distribution models for migratory birds: a gap in ecological forecasting.docx

Understanding the consequences of global change for migratory birds is complex as individuals are exposed to diverse conditions and experiences that interact across their annual cycle. Species distribution models (SDMs) can serve as a powerful tool that help us understand how species distributions respond to global change. However, SDMs applied to migratory birds may fail to capture the effects of seasonal variability on species distributional changes, likely due to a lack of appropriate modeling frameworks and limited data availability that hamper the inclusion of events and conditions throughout the annual cycle. Here, we review patterns in the migratory bird SDM literature over the last two decades using a vote counting approach, and provide a framework for migratory bird SDMs moving forward. We found evidence that species distribution models applied to migratory birds (1) typically incorporate data from only one season of the full annual cycle and do not account for seasonal interactions, (2) are focused on terrestrial species in North America and Europe, (3) tend to model the distributions of obligate migratory species, especially songbirds and waterfowl, and (4) largely lack biologically relevant threat layers. To improve our ability to forecast how species cope with global change, we recommend a Bayesian modeling framework where existing knowledge about a species’ migratory connectivity, threats, and/or other biologically relevant factors can be specified via model priors. Full annual cycle species distribution models are important tools for improving forecasts of migratory bird distributions in response to global change.</p

Songbirds initiate migratory flights synchronously relative to civil dusk

Abstract Background Each spring and fall billions of songbirds depart on nocturnal migrations across the globe. Theory suggests that songbirds should depart on migration shortly after sunset to maximize their potential for nightly flight duration or to time departure with the emergence of celestial cues needed for orientation and navigation. Although captive studies have found that songbirds depart during a narrow window of time after sunset, observational studies have found that wild birds depart later and more asynchronously relative to sunset than predicted. Methods We used coded radio tags and automated radio-telemetry to estimate the time that nearly 400 individuals from nine songbird species departed their breeding or wintering grounds across North America. We also assessed whether each species was most likely beginning long-distance migratory flights at departure or instead first making non-migratory regional flights. We then explored variation in nocturnal departure time by post-departure movement type, species, age, sex, and season. Results We found that 90% of individuals from species that were likely initiating long-distance migratory flights departed within 69 min of civil dusk, regardless of species, season, age, or sex. By contrast, species that likely first made non-migratory regional movements away from the migratory destination departed later and more asynchronously throughout the night. Regardless of post-departure movement type, 98% of individuals departed after civil dusk but otherwise showed no preference in relation to twilight phase. Conclusions Although the presence of celestial orientation cues at civil dusk may set a starting point for departure each night, the fact that species likely beginning long-distance migration departed earlier and more synchronously relative to civil dusk than those first making non-migratory regional movements is consistent with the hypothesis that departing promptly after civil dusk functions to maximize the potential for nightly flight duration and distance. By studying the onset of migration, our study provides baseline information about departure decisions that may enhance our understanding of departure timing throughout migration