Search

Hybridization between Cerulean Warbler (Setophaga cerulea) and Northern Parula (Setophaga americana) has been suggested from field observations at several sites in eastern North America, but without quantitative data to confirm this pairing. Here we present the first mensural and molecular evidence to confirm hybridization of these closely related species. Two suspected hybrids were detected based on atypical songs during the 2014 and 2015 breeding season in Summit County, Ohio, USA. Analysis of tissue samples, morphometric and plumage data showed a combination of Cerulean Warbler and Northern Parula plumage characteristics; the overall appearance resembled a Cerulean Warbler male but with white eye arcs, a weak yellow wash on the breast, and some yellow mantle feathers suggesting Northern Parula parentage. A mitochondrial and 2 nuclear genes were sequenced. Both individuals' mitochondrial sequences were identical to Cerulean Warbler sequences, indicating that both had a Cerulean Warbler dam. Sequences from nuclear genes had a total of 10 heterozygous loci, confirming that they were sired by Northern Parulas. These hybrids, and other reports, come from areas where Northern Parulas are expanding their breeding range into Cerulean Warbler range, suggesting that this hybrid combination may become more common. [ABSTRACT FROM AUTHOR]

Migrating birds congregate near the shores of Lake Erie during migration and may be funneled through small green spaces within the urban matrix of Great Lake coastal cities, where they are at risk of higher mortality from manmade structures. Bird deaths due to window collisions were assessed amongst a complex of low-rise buildings (<30 m) on a university campus in Cleveland, OH. A 1.8 km route was surveyed three times per week during a 12-month period. Deaths were tested against null hypotheses that season, taxonomy, and building attributes had no significant relationship with avian mortality. We recovered 271 dead birds of 50 species, all of which were consistent with regional bird lists and Neotropical-Nearctic and North American migrants through Ohio. Deaths occurred non-randomly by week, month, and migratory status with 90 percent of deaths occurring during spring and fall migrations. Consequently, migrants (warblers: 34 percent of species richness, 30 percent of deaths; sparrows: 14 percent of richness, 35 percent of deaths) were observed nine times more frequently than residents. Neotropical-Nearctic migrant species outnumbered North American migrant species. Although there was no statistical difference between the compass direction of a building facade and the number of deaths, deaths were not randomly distributed among campus buildings. Rather, significantly more deaths occurred at facades with higher percentages of glass. The presence of trees within 5 m of a window and the reflection of trees in windows were also associated with a greater risk of fatality. A better understanding of the factors associated with bird-window collisions is a pressing issue in the conservation of migratory birds. [ABSTRACT FROM AUTHOR]

Understanding interactions between biota and the built environment is increasingly important as human modification of the landscape expands in extent and intensity. For migratory birds, collisions with lighted structures are a major cause of mortality, but the mechanisms behind these collisions are poorly understood. Using 40 years of collision records of passerine birds, we investigated the importance of species' behavioural ecologies in predicting rates of building collisions during nocturnal migration through Chicago, IL and Cleveland, OH, USA. We found that the use of nocturnal flight calls is an important predictor of collision risk in nocturnally migrating passerine birds. Species that produce flight calls during nocturnal migration tended to collide with buildings more than expected given their local abundance, whereas those that do not use such communication collided much less frequently. Our results suggest that a stronger attraction response to artificial light at night in species that produce flight calls may mediate these differences in collision rates. Nocturnal flight calls probably evolved to facilitate collective decision-making during navigation, but this same social behaviour may now exacerbate vulnerability to a widespread anthropogenic disturbance. Our results also suggest that social behaviour during migration may reflect poorly understood differences in navigational mechanisms across lineages of birds.