by Carl Strang
Birds are the focus of this week’s literature feature.
Diane Colombelli-Négrel, Mark E. Hauber, Jeremy Robertson, Frank J. Sulloway, Herbert Hoi, Matteo Griggio, Sonia Kleindorfer. Embryonic Learning of Vocal Passwords in Superb Fairy-Wrens Reveals Intruder Cuckoo Nestlings. Current Biology, 2012; DOI: 10.1016/j.cub.2012.09.025
As described in a ScienceDaily article. They noticed that female superb fairy-wrens sing to their eggs, and they later demonstrated experimentally that the mothers were teaching their future nestlings a particular note, described by the authors as a password, that the nestlings would need to include in their begging calls to be fed. This note varies from nest to nest, and if the parents do not hear it they abandon. This is a novel way of dealing with nest parasites, in this case cuckoos, whose eggs and nestlings do not have the programming to learn and repeat the password.
Katzner, Todd, et al. 2012. Status, biology, and conservation priorities for North America’s eastern golden eagle (Aquila chrysaetos) population. Auk 129:168-176.
The eastern population estimate is 1000-2500 (east of the Mississippi River; western population 21,000-35,000). The species generally appears to be declining, though the eastern population has increased since the ban on DDT. Lead poisoning and incidental damage by leg-hold traps set for mammals are the biggest threats to eastern eagles. They are most abundant in Quebec, fewer in Ontario and Labrador as breeders. There has been no nesting in the eastern U.S. since the late 1990’s, the last ones in Maine and New York state. In Canada, nest sites are away from forested areas, mainly “at the interface of tundra, boreal forest, and wet meadows.” An estimated 15-25% migrate through the Great Lakes region. Wisconsin and Iowa host at least 70 birds in winter; the wintering status in Illinois is given as “unknown.”
W. Jetz, Thomas, G. H., Joy, J.B., Hartmann, K. & A.O. Mooers. The global diversity of birds in space and time. Nature, October 31, 2012.
As described in a ScienceDaily article. They did a combined fossil and DNA study of 10,000 bird species, and found unusual evolutionary diversification has been happening over the past 50 million years. Furthermore, the rate of new species appearance has not leveled off, but rather continued or even increased, in contrast to the usual pattern in which a foundational species diversifies but then a plateau is reached when available niches are filled. They attribute this difference to birds’ mobility, the opening of new habitats, and certain adaptable avian traits. Furthermore, there is no difference between speciation rates in the tropics and more polar regions, supporting a longer continuous history of tropical environments as being responsible for greater tropical diversity of birds (species accumulating, but extinction less rapid).
Stanley CQ, MacPherson M, Fraser KC, McKinnon EA, Stutchbury BJM (2012) Repeat Tracking of Individual Songbirds Reveals Consistent Migration Timing but Flexibility in Route. PLoS ONE 7(7): e40688. doi:10.1371/journal.pone.0040688
They followed individual wood thrushes over several migrations, and found that individuals showed little variation in spring migration departure date, and arrival date on territory, but much more flexibility in migration route and in fall departure date.
Brommer JE, Lehikoinen A, Valkama J (2012) The Breeding Ranges of Central European and Arctic Bird Species Move Poleward. PLoS ONE 7(9): e43648. doi:10.1371/journal.pone.0043648
They compared breeding bird atlases conducted in Finland, finding that there have been shifts northward in the centers of ranges for both northern and central European species. The shifts are happening slowly enough that surveys need to be taken decades apart. Northward advance of the northern edges of ranges is happening more quickly than extinctions at southern edges. The latter consideration is needed if range shifts are to be attributed to global climate change.