Members of the Clayton Lab also work on behavior, particularly defensive behavior of birds against ectoparasites. For example, we have done a good deal of research on the relationship of preening behavior to avian bill morphology. The beaks of Darwin’s finches and other birds are among the best known examples of adaptive evolution. Beak morphology is usually interpreted in relation to its critical role in feeding behavior. However, the beak also plays an important role in preening, which is the first line of defence against harmful ectoparasites such as feather lice, fleas, bugs, flies, ticks, and feather mites. We recently identified a feature of the beak specifically adapted for ectoparasite control. Experimental trimming of the tiny (1-2mm) maxillary overhang of Rock Pigeons (Columba livia) had no effect on feeding efficiency, yet triggered a dramatic increase in feather lice and the feather damage they cause. The overhang functions by generating a shearing force against the tip of the lower mandible, which moves forward remarkably quickly during preening, at up to 31 times per second (view preening video and relevant papers). This force damages parasite exoskeletons, significantly enhancing the efficiency of preening for parasite control. Overhangs longer than the natural mean of 1.6mm break significantly more often than short overhangs. Hence, stabilizing selection will favour overhangs of intermediate length. The adaptive radiation of beak morphology should therefore be re-assessed with both feeding and preening behavior in mind (Clayton et al. 2005 Proceedings of the Royal Society of London B  ).

We also work on the relationship of maintenance behavior (preening, scratching, bathing, sunning, etc) to sexual selection. Elaborate secondary sexual traits, such as the ornamental plumage of birds, are favored by female choice because they serve as honest indicators of male quality. Elaborate traits are thought to be honest signals because they are expensive to produce and increase predation risk. We have investigated another potential cost of elaborate traits, i.e. the time and energy required to maintain them in good condition. We tested the hypothesis that species of birds with ornamental plumage invest more time in maintenance behavior than do related species without such plumage. We call this the “High maintenance handicap hypothesis”. In a recent paper (Walther and Clayton 2005 Behavioural Ecology ) we show that ornamental species do indeed spend significantly more of their daily activity in maintenance behavior. Time spent on maintenance cannot be devoted to other activities. This temporal trade-off reinforces the honesty of ornamental plumage. We suggest that high maintenance handicaps are present in a variety of animals.

Finally, we also have a long-term “side” project concerning the evolution of echolocation behavior in cave-swiftlets.  Swiftlets are small, insectivorous birds found throughout the Australasian region from the Indian Ocean to the South Pacific. Most species roost and nest in caves, often placing their nests in areas of complete darkness, and are able to navigate using echolocation (Figure 1).  Unlike the ultrasonic cries of bats, the echolocation clicks of swiftlets are well within the human range of hearing and so presumably do not allow the acuity needed to locate aerial insect prey. Rather, studies of several species indicate that echolocation is used in swiftlets primarily for avoiding obstacles while flying in darkness when visual cues are not available. We are interested in the evolutionary history of echolocation (Figure 2).  For example, how many times has it evolved, and is it a useful phylogenetic character for this group of birds.

The following two figures are from Price et al. 2005. IBIS. 147:790-796.

Figure 1. Spectrogram of double clicks produced by Aerodramus papuensis while flying
outside of Losavi Cave, Papua New Guinea between 02:00 and 03:00h, 18 November 2002.

Figure 2. Echolocation reconstructed onto the maximum likelihood phylogeny of the swiftlets.