Documenting Molt-migration in Western Kingbird (Tyrannus verticalis) Using Two Measures of Collecting Effort

Stable Isotopes (δD) Reveal East–West Differences in Scheduling of Molt and Migration in Northern Rough-Winged Swallows (Stelgidopteryx serripennis)

“…All other JULY 2011 -MOLT SCHEDULING IN ROUGH-WINGED SWALLOWS -529 such cases have been discovered through examination of material in museum collections (Johnson 1963, Rohwer and Manning 1990, Butler et al 2002 or by recent field work (Butler et al 2006, Rohwer et al 2007, Barry et al 2009). Neotropical migrant passerines that breed in western North America but molt on their breeding range tend to be small species that require less time to replace their primaries (Rohwer et al 2009b), and some are known to move upslope to molt (Carlisle et al 2005a, b;Rohwer et al 2008).…”

The importance of range edges for an irruptive species during extreme weather events

“…In migratory birds, the processes involved in the 'push-pull' hypothesis can be seen during molt-migration, a phenomenon in which birds molt at a location in between their breeding and wintering range. This is where poor weather conditions causing low productivity on the breeding grounds appear to 'push' birds out, leading to a staged migration as birds are 'pulled' to areas with better productivity (Barry et al 2009;Fox and Walsh 2012). Movement of species that require resources or habitats that are especially dependent on suitable weather conditions, such as seasonal or semi-permanent water sources, may respond more to 'push' pressures by moving away from sub-optimal conditions.…”

Assessing Migratory Double Breeding through Complementary Specimen Densities and Breeding Records

“…On a much smaller scale, Barry et al (2009) showed that using total passerines as a measure of collecting effort gave departure times for adult Western Kingbirds (Tyrannus verticalis) that closely paralleled results obtained when collecting effort was assessed as adult kingbirds divided by the sum of adults and immature kingbirds in collections. That example and the results reported here suggest that using online databases to develop indices of collecting effort can provide useful and often difficult-to-determine information about the timing and location of seasonal movements of migratory species.…”

“…Abundance indices are particularly valuable for showing whether absences of certain categories of specimens results from those birds not being present at the time and place of interest or from lack of collecting (Barry et al 2009). They also illustrate when a species was collected in numbers beyond the background level of collecting, which we measure as the sum of all other passerines collected in the same region and time period.…”

“…Our graphs of total passerines also provide data needed to assess the effect on the abundance index of single additional (or fewer) specimens. Neither ORNIS nor the Mexican bird atlas distinguishes adult birds from juveniles, so declines in abundance in the fall do not reflect accurately the departure of breeding adults in species in which juveniles migrate later than adults, frequent when adults migrate before molting but juveniles replace body plumage before their fall migration (Rohwer et al 2005, Barry et al 2009). …”