Temporal Migration Patterns Between Natal Locations of Ruby-Throated Hummingbirds (\u3ci\u3eArchilochus colubris\u3c/i\u3e) and Their Gulf Coast Stopover Site

Background Autumn latitudinal migrations generally exhibit one of two different temporal migration patterns: type 1 where southern populations migrate south before northern populations, or type 2 where northern populations overtake southern populations en route. The ruby-throated hummingbird (Archilochus colubris) is a species with an expansive breeding range, which allows opportunities to examine variation in the timing of migration. Our objective was to determine a relationship between natal origin of ruby-throated hummingbirds and arrival at a Gulf coast stopover site; and if so, what factors, such as differences in body size across the range as well as the cost of migration, might drive such a pattern. To carry out our objectives, we captured hummingbirds at a coastal stopover site during autumn migration, at which time we collected feathers from juveniles for analysis of hydrogen stable isotopes. Using the hydrogen stable isotope gradient of precipitation across North America and published hydrogen isotope values of feathers from populations of breeding ruby-throated hummingbirds, we assigned migrants to probable natal latitudes. Results Our results confirm that individuals from across the range (30–50° N) stopover along the Gulf of Mexico and there is a positive relationship between arrival day and latitude, suggesting a type 1 migration pattern. We also found no relationship between fuel load (proxy for migration cost) or fat-free body mass (proxy for body size) and natal latitude. Conclusions Our results, coupled with previous work on the spatial migration patterns of hummingbirds, show a type 1 chain migration pattern. While the mechanisms we tested do not seem to influence the evolution of migratory patterns, other factors such as resource availability may play a prominent role in the evolution of this migration system

Swainson\u27s Thrushes Do Not Show Strong Wing Selectivity Prior to Crossing the Gulf of Mexico

During long-distance fall migrations, nocturnally migrating Swainson’s Thrushes often stop on the northern Gulf of Mexico coast before flying across the Gulf. To minimize energetic costs, trans-Gulf migrants should stop over when they encounter crosswinds or headwinds, and depart with supportive tailwinds. However, time constrained migrants should be less selective, balancing costs of headwinds with benefits of continuing their migrations. To test the hypotheses that birds select supportive winds and that selectivity is mediated by seasonal time constraints, we examined whether local winds affected Swainson’s Thrushes’ arrival and departure at Ft. Morgan, Alabama, USA at annual, seasonal, and nightly time scales. Additionally, migrants could benefit from forecasting future wind conditions, crossing on nights when winds are consistently supportive across the Gulf, thereby avoiding the potentially lethal consequences of depleting their energetic reserves over water. To test whether birds forecast, we developed a movement model, calculated to what extent departure winds were predictive of future Gulf winds, and tested whether birds responded to predictability. Swainson’s Thrushes were only slightly selective and did not appear to forecast. By following the simple rule of avoiding only the strongest headwinds at departure, Swainson’s Thrushes could survive the 1500 km flight between Alabama and Veracruz, Mexico

Competition and habitat quality influence age and sex distribution in wintering rusty blackbirds.

Bird habitat quality is often inferred from species abundance measures during the breeding and non-breeding season and used for conservation management decisions. However, during the non-breeding season age and sex classes often occupy different habitats which suggest a need for more habitat-specific data. Rusty Blackbird (Euphagus carolinus) is a forested wetland specialist wintering in bottomland hardwood forests in the south-eastern U. S. and belongs to the most steeply declining songbirds in the U.S. Little information is available to support priority birds such as the Rusty Blackbird wintering in this threatened habitat. We assessed age and sex distribution and body condition of Rusty Blackbirds among the three major habitats used by this species in the Lower Mississippi Alluvial Valley and also measured food availability. Overall, pecan groves had the highest biomass mainly driven by the amount of nuts. Invertebrate biomass was highest in forests but contributed only a small percentage to overall biomass. Age and sex classes were unevenly distributed among habitats with adult males primarily occupying pecan groves containing the highest nut biomass, females being found in forests which had the lowest nut biomass and young males primarily staying in forest fragments along creeks which had intermediate nut biomass. Males were in better body condition than females and were in slightly better condition in pecan groves. The results suggest that adult males occupy the highest quality habitat and may competitively exclude the other age and sex classes

Stopover Biology of Ruby-Throated Hummingbirds (\u3ci\u3eArchilochus colubris\u3c/i\u3e) During Autumn Migration

Surprisingly little is known about the migration and stopover biology of Ruby-throated Hummingbirds (Archilochus colubris), and even less is known about their sex-or age-dependent migration. First, we provide basic information on the migration and stopover biology of this species along the northern coast of the Gulf of Mexico during autumn, including phenology, stopover duration, fuel deposition rate (FDR), arrival mass, and estimated flight ranges. Second, we investigate whether these stopover variables are influenced by age or sex. Age-dependent migration is expected because young, hatch-year birds on their first migration lack the experience of older individuals. Sex-dependent migration is expected because of sexually dimorphic characteristics in wing morphology and body size. We obtained information on arrival mass, phenology, FDR, stopover duration, and estimated flight ranges through banding data, passive integrated transponder tags, radio telemetry, and color marking at a long-term migration station along the northern coast of the Gulf of Mexico. Our data provide strong evidence for age-dependent migration and only weak evidence for sex-dependent migration. Older birds arrived earlier, had larger fuel loads, and had shorter stopover durations than younger birds. In younger birds, we found no effect of sex on FDR, arrival mass, stopover duration, or phenology. Older males arrived with larger fuel loads than females. Finally, we used flight simulation software and our data to estimate that males and older birds were capable of longer potential flight ranges than either females or younger birds

An Indigo Buntin (\u3ci\u3ePasserina cyanea\u3c/i\u3e) Transporting Snails During Spring Migration

Organisms with limited motility may use animal transport as a mechanism for dispersal. Migratory birds can provide a vehicle to move small organisms great distances, which may allow them access to areas that are otherwise inaccessible. During normal mist netting operations at a spring migration banding station along the northern Gulf of Mexico coast in Louisiana, USA, we encountered an Indigo Bunting (Passerina cyanea) with numerous snails, possibly Galba cubensis, underneath its breast feathers. While encounters of songbirds carrying snails appear rare, long-distance migrating songbirds represent a possible mechanism to transport small snails great distances to expand ranges, colonize new areas, or maintain genetic continuity

A Tennessee Warbler (\u3ci\u3eLeiothlypis peregrina\u3c/i\u3e) Captured In the Web of a Golden Silk Orb-Weaver (\u3ci\u3eTrichonephila clavipes\u3c/i\u3e)

During migration, transient birds usually find themselves stopping in unfamiliar habitats in order to rest and refuel before resuming migratory flight. Here we document the first case, to our knowledge, of a Tennessee Warbler (Leiothlypis peregrina) entrapped in a spiderweb. The warbler\u27s tarsus became caught in the mooring thread of a golden silk orb-weaver (Trichonephila clavipes) web and the bird was unable to free itself, resulting in death. While the role of spiderweb-related mortalities is likely minimal, they may represent a type of additive mortality that has been largely unconsidered during migration. Given the spatiotemporal overlap in the prevalence of spiderwebs and movement of migratory birds, researchers should document and report such anecdotal observations to determine the role spiders may play in mortality events during migration

Local Weather and Endogenous Factors Affect the Initiation of Migration in Short‐ and Medium‐Distance Songbird Migrants

Migratory birds employ a variety of mechanisms to ensure appropriate timing of migration based on integration of endogenous and exogenous information. The cues to fatten and depart from the non-breeding area are often linked to exogenous cues such as temperature or precipitation and the endogenous program. Shorter distance migrants should rely heavily on environmental information when initiating migration given relatively close proximity to the breeding area. However, the ability to fatten and subsequently depart may be linked to individual circumstances, including current fuel load and body size. For early and late departing migrants, we investigate effects of temperature, precipitation, lean body mass, fuel load and day of year on the initiation of migration (i.e. fuel load and departure timing) from the non-breeding region by analyzing 21 years of banding data for four species of short- and medium-distance migrants. Temperatures at the non-breeding area were related to temperatures at potential stopover areas. Despite local cues being predictive of conditions further north, the amount variation explained by local weather conditions in our models differed by species and temporal period but was low overall (< 33% variation explained). For each species, we also compared lean body mass and fuel load between early and late departing migrants, which showed mixed results. Our combined results suggest that most individuals migrating short or medium distances in our study did not time the initiation of migration with local predictive cues alone, but rather other factors such as lean body mass, fuel load, day of year, which may be a proxy for the endogenous program, and those beyond the scope of our study also influenced the initiation of migration. Our study contributes to understanding which factors influence departure decisions of short- and medium-distance migrants as they transition from the non-breeding to the migratory phase of the annual cycle

Fine-scale heterogeneity drives forest use by spring migrant landbirds across a broad, contiguous forest matrix

© 2018 American Ornithological Society. Much of our understanding of en route landbird habitat use comes from research performed at local scales, ignoring effects at larger spatial scales. We used a multiscale approach to investigate stopover habitat use by landbirds using transect surveys in 68 forested sites in southwestern Michigan, USA, during the springs of 2002 and 2003. We modeled relationships of bird density and arthropod abundance with broad-scale spatiotemporal factors (year, day of year, geographic location) and local landscape (forest composition and structure, presence of open water) as well as sitescale factors (bird density and arthropod abundance, which exchanged roles as predictor and response variables). We found migrant densities to be most influenced by fine-scale factors, such as the abundance of other avian taxa and substrate arthropods, followed by broader-scale factors, such as forest structure and location, within the local and broader surrounding landscape. We found that migrant habitat associations either did not directly match or were weakly associated with the availability of riparian or lacustrine water habitats at a local scale, even though our results suggested that birds using these habitat cues would have encountered more arthropods. Rather than finding indirect measures of food abundance-such as distance to a water source or forest cover at the landscape scale-important, our models best explained bird density by a direct relationship with site-scale food resources. Thus, the scale at which migrants demonstrate habitat selection appears to be influenced by proximate mechanisms such as high-quality habitat availability and the presence of large ecological features within the landscape. Not only do factors operating at multiple scales influence how birds use habitats, but scale also influences how we interpret research findings, in turn influencing conservation decisions