Today’s column will be a review of recently published articles in ornithology that I hope will be of interest.
Foot waggling in Common Loons
If you have spent much time watching Common Loons, you surely have seen a loon on the water raise one foot into the air and either hold it there briefly or shake it, often several times in succession. This behavior is called a foot waggle. After waggling the foot, a loon may put the foot under the wing, a behavior called shipping.
The reasons for foot waggling have been discussed for years but not adequately tested. Some ornithologists suggest foot waggling occurs most frequently in birds that are about to sleep or rest and interpret foot waggling as a comfort movement. Other scientists think that the large foot of the loon with its extensive system of capillaries may be used to regulate body temperature. A foot out of the water might lose heat quickly by evaporation of water into the air. Other ornithologists have suggested that food waggling may function as a social signal.
A recent paper in the Condor by James Paruk describes his work to investigate the function of the loon foot waggle at several sites in the Upper Peninsula of Michigan. He found that 81% of the foot waggles observed occurred while a loon was either preening or resting. Foot waggling was therefore judged to be primarily a comfort movement. Occasionally, a loon would give a single foot waggle in a stressful situation such as after encounters with boaters or a Bald Eagle or after loud thunder. Because only some loons used the foot waggle in such situations, Paruk claims that the behaviors are idiosyncratic – some birds use the behavior and others do not.
The loons did waggle their feet more on sunny days than on cloudy days. The dark bodies of loons heat up more in direct sunlight. This relationship suggests that regulating body temperature may be a secondary function of foot waggling.
By the way, foot waggling is seen in other aquatic birds as well including grebes, Ruddy Ducks, scaups and their relatives, and mergansers.
Tail pumping in Eastern Phoebes
The tail-pumping behavior of a perched phoebe is a good feature to use in identifying this flycatcher. The function of this behavior has been the subject of much conjecture. Michelle Carder and Gary Ritchison recently published an article in the Journal of Field Ornithology that presents a test of possible explanations for the behavior.
They tested four hypotheses by extensive field observations. The first is that phoebes use tail pumping to maintain their balance on a perch. The authors measured tail-pumping rates on perches of different stability (thin versus thick branches) and under different wind speeds. They found no correlations and reject this explanation. A second hypothesis was that phoebes use tail pumping as a territorial display to other males. Through playback experiments, this explanation was also rejected.
Thirdly, tail pumping might be use to aid foraging by flushing insects. The authors found no support for this hypothesis.
The predator-deterrent hypothesis was supported by the author’s data. A phoebe should increase its tail wagging in the presence of a predator to let the predator know “I see you”. Lower rates of tail wagging when predators are not seen may discourage those predators from attacking a phoebe.
Altitudinal ranges of birds and climate change
As global warming proceeds, marked changes occur in the climate of mountains. The warming means that species restricted by temperature can move higher up a mountain.
For mobile species like birds, scientists expect that the distribution along an altitudinal gradient will occur. Birds must move higher up a mountain to find the temperature regime that best suits them.
Recently, Morgan Tingley and colleagues published a paper that explores this phenomenon. They resurveyed bird abundance in the Sierra Nevada mountains of California along four elevational transects, first established nearly a century ago. Climate information indicates that any site along the transects is warmer now than it was a century ago. The workers focused on 53 bird species and found that 48 of them had shifted their range higher up the mountains over the past century.
[Originally published on October 18, 2009]