Cryptic speciation in a Holarctic passerine revealed by genetic and bioacoustic analyses

There has been much controversy regarding the timing of speciation events in birds, and regarding the relative roles of natural and sexual selection in promoting speciation. Here, we investigate these issues using winter wrens ( Troglodytes troglodytes ), an unusual example of a passerine with a Holarctic distribution. Geographical variation has led to speculation that the western North American form Troglodytes troglodytes pacificus might be a distinct biological species compared to those in eastern North America (e.g. Troglodytes troglodytes hiemalis ) and Eurasia. We located the first known area in which both forms can be found, often inhabiting neighbouring territories. Each male wren in this area sings either western or eastern song, and the differences in song are as distinct in the contact zone as they are in allopatry. The two singing types differ distinctly in mitochondrial DNA sequences and amplified fragment length polymorpism profiles. These results indicate that the two forms are reproductively isolated to a high degree where they co-occur and are therefore separate species. DNA variation suggests that the initial split between the two species occurred before the Pleistocene, quite long ago for sister species in the boreal forest. Surprisingly, the two forms are similar in morphometric traits and habitat characteristics of territories. These findings suggest that sexual selection played a larger role than habitat divergence in generating reproductive isolation, and raise the possibility that there are other such morphologically cryptic species pairs in North America.     

Factors affecting songbird communities using new short rotation coppice habitats in spring

The aim of this study was to describe the songbird communities occupying willow and poplar short rotation coppice (SRC) crops during the breeding season, and to identify the features of existing plantations that affect their abundance. Songbird point-counts were undertaken at 66 different plots of SRC at 29 sites throughout Britain and Ireland during spring 1993. Measures of vegetation and coppice management in each plot were also taken. The songbird species using the SRC survey plots were similar to those reported from traditional coppice habitats. Willow SRC contained more resident and migrant songbird species than poplar SRC. Warbler species and buntings in particular were rarely recorded from poplar plots. Finches, tits and thrushes were recorded equally from both willow and poplar. More migrant species were recorded from year 2 willow coppice (i.e. in its third growth season since winter cutting) than in either year 1 or year 3. Most resident species selected older willow or poplar coppice growth up to year 3 or 4, the oldest age classes in the sample. These 4-year trends for migrant and resident songbirds are similar to those observed in traditional coppice woodland over a 10- or 12-year rotation. Skylark and Meadow Pipit were recorded from recently cut SRC plots (year 0). In a regression analysis, the number of songbird species and individuals, particularly migrants, were found to be positively related to the increased structural density or complexity of the coppice vegetation.     

Lack of predator‐odor detection and avoidance by a songbird,the House Wren

ABSTRACT Recent studies suggest that songbirds have a better sense of smell than initially suspected. Work is now focused on determining how birds use their sense of smell to enhance survival and reproduction. One question is whether birds use smell to detect and avoid predators. We examined the reaction of House Wrens (Troglodytes aedon) to the odor of a potential predator in their nests. On two different days of the nestling stage, we placed papers infused with the urine and anal scent gland material of a mustelid (American mink, Neovison vison), a neutral odoriferous substance (cologne, garlic, or vinegar), or water in nest boxes. The proportion of individuals that hesitated to enter nest boxes after first arrival did not differ significantly between treatments on either day. We also found no significant differences on either day in the time it took wrens to first enter nest boxes, time spent in nest boxes after first entry, the propensity to stay in nest boxes and brood young, or latency to return to nest boxes after first exposure to treatments. Our results suggest that House Wrens either did not detect or did not respond to foreign odors in nest cavities, including the odor of a mustelid predator. In a similar study ( Amo et al. 2008 . Functional Ecology 22: 289–293), adult Blue Tits (Cyanistes caeruleus) were less likely to enter nest boxes that contained the odor of a mustelid. One explanation for this difference is that Blue Tits may have a better sense of smell than House Wrens. Alternatively, or additionally, Blue Tits may be inherently (or as result of experience) more prone than House Wrens to avoid unusual odors or, specifically, the odor of mustelid predators in their nests. Additional studies are needed to determine the extent to which songbirds use their sense of smell to detect and avoid nest predators.