Thursday, March 28, 2013

Bridget Stutchbury's book, "The Private Lives of Birds"

I’ve been reading a fascinating book by Bridget Stutchbury, The Private Lives of Birds: A Scientist Reveals the Intricacies of Avian Social Life. The book came out in 2010, but I didn’t read it until recently. Bridget Stutchbury is a well-known researcher at York University in Toronto. She specializes in the behavioral ecology of migratory songbirds, and achieved international fame when she placed geolocators—tiny tracking devices—on Purple Martins and Wood Thrushes during one breeding season and retrapped the birds the following spring.

Geolocators are very tiny—one device and the harness used to hold it just above a bird’s rump weigh less than one gram. All a geolocator does is to record light levels and the time of day, and scientists must retrap a bird and remove the geolocator to retrieve any data, so the technology is useful only for species with high site fidelity, likely to be caught again the following year. Day-length varies with latitude and the time of solar noon varies with longitude. Data from a geolocator can reveal a bird’s entire migratory path and where it spent the winter accurately to about 125 miles for latitude. They provide much better resolution for longitude. Satellite tracking devices, used on loons, osprey, and other large birds, are significantly more precise but much too heavy for songbirds. Scientists don’t put any device weighing more than 4 percent of a bird’s body weight on it. Geolocators are tiny enough to weigh more like 2 percent of the weight of medium-sized songbirds such as thrushes and martins, and for now provide the best information we have for working out migration and wintering locations for Neotropical songbirds.

  This information is extremely useful not just for learning cool stuff about various birds, but also because in many species, local breeding populations may winter in different locations from other breeding populations of the same species. Some birds of conservation importance have robust populations in one state but may be declining dangerously in another. The problems causing a decline may be due to factors on the breeding grounds, but may also arise along the migration route or on the wintering grounds. Without knowing the migration pathways and wintering areas for different populations, we have no way of figuring out what is going wrong in one case but not the other, and have no chance to try to correct it.

 Bridget Stutchbury’s seminal research led to her 2007 book, The Silence of the Songbirds, subtitled "How we are losing the world’s songbirds and what we can do to save them," a wonderful book I devoured as soon as it came out. She also is co-author of a fantastic textbook, Behavioral Ecology of Tropical Birds, published in 2001. So her Private Lives of Birds is based on a vast body of research put together by her and her students through her career, using state-of-the-art technology and good old fashioned field work.

It’s a fun read, because she elegantly explains how she and other researchers figure out each piece of information even as she’s keeping her focus on exactly what the title says, the private lives of birds. For example, scientists banding nesting birds have long known that most songbirds are monogamous. So they were mystified when DNA analysis in more and more species established that a single brood of nestlings raised by supposedly monogamous birds all were likely to have the same mother but one or more of the chicks may have been fathered by one or more males other than the one raising them. Stutchbury explains the advantages to birds of this “extra-pair paternity,” and explains what male birds do to try to keep their own mates faithful even as they try to mate with other females.

Her writing is fun and accessible as well as authoritative. Here and there she or her editors made minor errors: one does not see large numbers of crocodiles on a Texas island. And sometimes I squirmed thinking about the individual birds that were experimented upon for her to make many of her discoveries. It sounds like she didn't "sacrifice" any birds, but trapping one of a mated pair and keeping it off territory for hours or days to see whether it could get the territory back was probably pretty unpleasant for both that bird and the one trying to take over the territory. Fortunately, she has a track record of using the valuable information from these experiments to promote bird conservation that ultimately can benefit those individual birds as well as larger populations.

The book is chock full of valuable facts and insights, and is well worth reading for anyone who wants to understand more about the private lives of birds.