of the Clayton-Bush 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).
Other recent papers concerning the role of preening for combating ectoparasites include the following:
Clayton, D. H. J. A. H. Koop, C. W. Harbison, B. R. Moyer and S. E.
Bush. 2010. How birds combat ectoparasites. Open Ornithology Journal 3:
41-71. (invited review for special issue: Currrent Issues in Avian
Koop, J. A. H., S. K. Huber and D. H. Clayton. 2012. Does sunlight
enhance the effectiveness of avian preening for ectoparasite control? J. of
Parasitology 98: 46-48.
Waite, J. L., A. R. Henry and D. H. Clayton. 2012. How effective is
preening for controlling mobile ectoparasites? An experimental
test with pigeons and hippoboscid flies.
International Journal of Parasitology. 42:463-467
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
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.
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
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.
following two figures are from Price et al. 2005. IBIS. 147:790-796.
1. Spectrogram of double clicks produced by Aerodramus
papuensis while flying
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.