For the Birds – Talks at the Ecological Society of America meeting
I recently returned from Memphis where I attended the annual meeting of the Ecological Society of America. In this column, I will review several talks I attended on birds to give you an idea of some new research being done on birds.
Gabriel Colbeck of Washington State University is conducting doctoral research on Black-throated Blue Warblers at the Hubbard Brook Forest in New Hampshire. Specifically, Colbeck is interested in the acoustics of bird song.
We know that low frequency sounds (lower pitched sounds) carry better through dense habitat than higher frequency sounds. Also sounds with slower elements tend to be distorted less in dense habitat than sounds with faster elements.
Colbeck is seeking to determine if Black-throated Blue Warblers adjust their characteristic buzzy “zur zur zur zwee” song to the nature of the habitat. Colbeck compared areas in Hubbard Brook that were damaged by the ice storm of January, 1998 to undamaged areas. In the damaged area, the ice storm downed many canopy trees and now the understory is dense with shrubs and saplings, contrasting with the more open understory of undisturbed areas.
Black-throated Blue Warblers sing a high- and low-frequency song. Colbeck expected low-frequency songs to be given more in the disturbed areas but found no difference in the proportion of these two types of songs in the disturbed and undisturbed habitats. He did however find that slower paced songs were more prevalent in the dense, disturbed area. The results suggest that these warblers adjust the nature of their songs to acoustic features of their environment.
Rebecca Tittler and colleagues at Carleton University in Ottawa presented a paper on dispersal distances of North American songbirds. The authors seek to determine how far breeding birds in one year moved from either their breeding site in the previous year or, for birds in their first breeding season, from the site where they were born. The authors used the Breeding Bird Survey (BBS) dataset to examine changes in abundance of 51 species from one year to the next. The authors looked for a high number of birds along BBS routes in the year after a high number of birds on a BBS route within the same state or country. The results suggest that songbirds disperse between 5 and 60 miles between years, a value much larger than previous work based on recapture of banded birds.
David Brown of Lousiana State University and Tom Sherry of Tulane reported on the wintering behavior of Ovenbirds in Jamaica. Two classes of birds were found: sedentary birds that have a fixed home range overlapping with neighbors and floaters that shift their habitat based on food availability. The classes were not related to age or sex.
Finally, Dee Boersma of the University of Washington gave a fascinating talk on Magellanic Penguins. She has been studying the largest colony of these penguins in the world at Punta Tomba along the south coast of Argentina for the past 22.
The climate at this site is temperate and the penguins nest on beaches above the tideline in burrows in the sand. The burrows are usually adjacent to a small bush that provides shade. Over the past 22 years, this population has decreased by 80%.
Two eggs are laid in the burrow of each pair. The mother and father take turns incubating the eggs with each shift lasting ten to 15 days. The eggs hatch after seven weeks. The chicks are incubated for an additional five weeks. Immediately after relinquishing incubation duties, the very hungry parent heads out to sea to feed on small fish and squid.
Using satellite transmitters placed on the backs of some male Magellanic Penguins, Boersma has shown that the penguins are now swimming much farther north and seaward to feed. Global climate change is proposed reason for this change in foraging behavior. Warmer ocean waters may have forced the preferred food of these penguins to be found in cooler offshore waters. Climate change may have affected the ocean currents along the coast as well.
The upshot is that the penguins must swim farther to find enough food to replace their fat reserves before they come back to take their mate’s place in incubating. It is possible at some point that an incubating parent may be forced to abandon the nest if the other parent is away foraging for too long.
Penguins that arrive late on the breeding grounds tend to be in poorer physiological condition, lay smaller eggs and have lower reproductive success. The late arrival is also driven by the necessity to feed farther offshore than in earlier years of the study.
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at [email protected] Previous columns and other information on Maine birding can be found at his blog: http://www.mainebirds.blogspot.com/