David J. T. Hussell

Cross-hemisphere migration of a 25 g songbird

The northern wheatear (Oenanthe oenanthe) is a small (approx. 25 g), insectivorous migrant with one of the largest ranges of any songbird in the world, breeding from the eastern Canadian Arctic across Greenland, Eurasia and into Alaska (AK). However, there is no evidence that breeding populations in the New World have established overwintering sites in the Western Hemisphere. Using light-level geolocators, we demonstrate that individuals from these New World regions overwinter in northern sub-Sahara Africa, with Alaskan birds travelling approximately 14 500 km each way and an eastern Canadian Arctic bird crossing a wide stretch of the North Atlantic (approx. 3500 km). These remarkable journeys, particularly for a bird of this size, last between one to three months depending on breeding location and season (autumn/spring) and result in mean overall migration speeds of up to 290 km d−1. Stable-hydrogen isotope analysis of winter-grown feathers sampled from breeding birds generally support the notion that Alaskan birds overwinter primarily in eastern Africa and eastern Canadian Arctic birds overwinter mainly in western Africa. Our results provide the first evidence of a migratory songbird capable of linking African ecosystems of the Old World with Arctic regions of the New World.

Changes in adult mass associated with the nesting cycle in the European starling

We manipulated broods of European Starlings to produce brood sizes of 3, 5, and 7 nestlings, and recorded the masses of adults throughout the nesting cycle. Males generally weighed more than females except during the laying period. Both sexes lost mass during the incubation and nestling periods, although the loss of somatic mass was most pronounced during the early part of the nestling period. Only at the end of the nestling period, and only among males, was body mass inversely related to the mass of the brood at the time of weighing. Repeated weighings of individuals during the second half of the nestling period revealed that females lost more mass than males, and adults rearing broods of 5 lost more than those rearing brooks of 3, although the average rate of loss was only 0.1 g day-1. Although mass loss is clearly associated with breeding and there are some indications that it is associated with level of effort, our results did not reveal convincing evidence for physiological stress.

Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America

Data from the North American Breeding Bird Survey (BBS) suggest that populations of aerial insectivorous birds are declining, particularly in northeastern regions of the continent, and particularly since the mid-1980s. Species that use nest boxes, such as Tree Swallows (Tachycineta bicolor), may provide researchers with large data sets that better reveal finer-scale geographical patterns in population trends. We analyzed trends in occupancy rates for ca. 40,000 Tree Swallow nest-box-years from 16 sites across North America. The earliest site has been studied intensively since 1969 and the latest site since 2004. Nest box occupancy rates declined significantly at five of six (83%) sites east of -78° W longitude, whereas occupancy rates increased significantly at four of ten sites (40%) west of -78° W longitude. Decreasing box occupancy trends from the northeast were broadly consistent with aspects of a previous analysis of BBS data for Tree Swallows, but our finding of instances of increases in other parts of the continent are novel. Several questions remain, particularly with respect to causes of these broadscale geographic changes in population densities of Tree Swallows. The broad geographic patterns are consistent with a hypothesis of widespread changes in climate on wintering, migratory, or breeding areas that in turn may differentially affect populations of aerial insects, but other explanations are possible. It is also unclear whether these changes in occupancy rates reflect an increase or decrease in overall populations of Tree Swallows. Regardless, important conservation steps will be to unravel causes of changing populations of aerial insectivores in North America. RESUME. Les donnees provenant du Releve des oiseaux nicheurs (BBS) de l’Amerique du Nord semblent indiquer que les populations d’insectivores aeriens sont en declin, particulierement dans les regions du nord-est du continent et depuis le milieu des annees 1980. Grâce aux especes qui utilisent les nichoirs, comme l’Hirondelle bicolore (Tachycineta bicolor), les chercheurs ont acces a une grande quantite de donnees qui revelent davantage les tendances des populations a l’echelle fine. Nous avons analyse la tendance du taux d’occupation par l’Hirondelle bicolore a partir de 40 000 nichoirs-annees provenant de 16 sites repartis en Amerique du Nord. Le site le plus ancien est suivi intensivement depuis 1969 et le plus recent, depuis 2004. Le taux d’occupation des nichoirs a diminue significativement dans 5 des 6 sites (83 %) situes a l’est du 78° de longitude ouest, tandis qu’il a augmente significativement dans 4 des 10 sites (40 %) a l’ouest du 78° de longitude ouest. La tendance a la baisse de l’occupation observee dans le nord-est concorde dans les grandes lignes avec les resultats d’une analyse anterieure des donnees du BBS pour cette espece, mais les hausses que nous avons observees dans d’autres regions de l’Amerique du Nord s’averent nouvelles. Plusieurs interrogations demeurent, notamment en ce qui a trait aux causes de ces changements dans la densite des populations d’Hirondelles bicolores a grande echelle. Ces vastes tendances geographiques concordent avec l’hypothese de changements climatiques generalises qui toucheraient les aires d’hivernage, de migration ou de nidification, lesquels pourraient affecter differemment les populations d’insectes aeriens, mais d’autres explications sont aussi possibles. En outre, nous ne savons pas si ces changements du taux d’occupation refletent une hausse ou une baisse dans l’ensemble des populations d’Hirondelles bicolores. Neanmoins, pour assurer leur conservation, il sera important d’elucider les causes des changements de populations chez les insectivores aeriens en Amerique du Nord.

Monitoring songbird population change with autumn mist netting

Counts of migrating birds potentially could be used to detect population change. This technique would be especially valuable for tracking species poorly monitored by breeding and wintering season counts, such as boreal-nesting songbirds that winter in the tropics. Numbers of migrants counted vary with weather and other factors, however, and we need to demonstrate that migration counts give accurate results. Population trends for 1979-91 were calculated for 13 songbird species captured during autumn mist netting at 2 sites in southern Michigan. All species were northern-nesters occurring at the study sites only as transients. Annual indices of abundance were derived from a multiple regression of daily number of newly-captured birds on independent variables for date, weather, moon phase and year. Trends in the annual capture indices were significantly and positively correlated with trends in breeding bird survey (BBS) data from presumed breeding grounds in Michigan and Ontario, and were of similar magnitude. The results suggest that intensive, standardized netting can be a useful population monitoring tool.

Breeding between Tree Swallows from the same brood

Abstract We provide data on three instances where Tree Swallows (Tachycineta bicolor) that fledged from the same nest (broodmates) eventually bred together in subsequent years. Two instances were detected in Ontario and a third was detected in Nova Scotia. Based on demographics at the times of each event, we estimated probabilities of these broodmate pairings as approximately 1 in 16,000, 1 in 5600, and 1 in 29,000, respectively, whereas the number of identified pairs in the populations was less than 65 in each case. Thus, inbreeding occurred at a higher frequency than expected by chance. We cannot distinguish whether these identical natal dispersal responses arose from similarity in genes or in rearing environments.