|ognizant Communication Corporation|
VOLUME 13, NUMBER 2, 2000
Bird Behavior, Vol. 13, pp. 63-67, 2000
1056-1383/00 $20.00 + .00
Copyright © 2000 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.
Responses of Scissor-Tailed Flycatchers (Tyrannus forficatus) to Experimental Cowbird Parasitism
Brian D. Peer and Spencer G. Sealy
Department of Zoology, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
We experimentally parasitized nests of scissor-tailed flycatchers (Tyrannus forficatus) in southern Texas with model bronzed cowbird (Molothrus aeneus) eggs and real and model brown-headed cowbird (M. ater) eggs. Twenty of 21 bronzed cowbird eggs were rejected an average of 3 days (range 1-11 days) after they were placed into nests, and all 20 brown-headed cowbird eggs were rejected after an average of 2 days (range 1-4 days). Three bronzed cowbird eggs were rejected after more than 5 days, which suggests that rejection frequencies in some studies have been underestimated because most researchers generally use 5 days as a cutoff for the length of time to eject parasitic eggs. Our data confirm that the scissor-tailed flycatcher is a rejecter species and that egg rejection may account for the lack of observed parasitism on this species. However, it is more likely that cowbirds seldom parasitize scissor-tailed flycatchers because some instances of natural parasitism should have been detected given the length of time required to reject experimentally introduced cowbird eggs.
Key words: Scissor-tailed flycatchers; Bronzed cowbirds; Brown-headed cowbirds; Egg rejection; Brood parasitism
Simulated Host Activity Does Not Attract Parasitism by Brown-Headed Cowbirds (Molothrus ater)
Paula M. Grieef and Spencer G. Sealy
Department of Zoology, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
Avian brood parasites such as the brown-headed cowbird (Molothrus ater) use a variety of features in their environments to locate potential host nests. We examined nest concealment and simulated parental activity in eliciting parasitism by cowbirds on nests of the clay-colored sparrow (Spizella pallida). We also measured the defensive responses of sparrows to freeze-dried mounts of a female cowbird, predators and control species to simulate activity at three distances from the nest. The degree of nest concealment did not affect the outcome of active nests. None of the nests in any of the five levels of simulated parental activity was parasitized, but depredation occurred in all but one treatment. Parental responses probably cannot be used to locate nests because clay-colored sparrows did not act defensively toward the cowbird mounts.
Key words: Brood parasitism; Host activity; Host selection; Brown-headed cowbird; Clay-colored sparrow
Orientation of Perching Birds When the Sun Is at Low Elevation
Michael J. Justice,1 Teresa C. Justice,2 and Kimberly C. Joyner2
1East Carolina University, Greenville, NC
2Chowan College, Murfreesboro, NC
A popular explanation for the dark dorsum/light ventrum color pattern seen in many avian species is crypsis through countershading. However, effective crypsis is dependent on the location of the sun in the sky and the orientation of the bird. When the sun is at low elevation, a bird would have to face its dorsum toward the sun to be countershaded. Facing its ventrum toward a low-lying sun would enhance the dorso-ventral contrast and increase conspicuousness. Thus, varying conspicuousness may be a cause of orientation behavior or a consequence of other factors affecting orientation. This study sought to determine whether some bird species orient with respect to the sun in a nonrandom fashion. To do this, the angle of perches with respect to the sun was quantified in 20 common North American bird species. Seven species faced the sun more often than expected, while the other 13 species failed to reject the null hypothesis of random orientation. These data suggest that orientation with respect to the sun is biologically significant for some avian species, but it is unclear which specific aspects of color or life history are associated with orientation toward the sun.
Key words: Orientation; Countershading; Bird color; Communication
Recovery of Cached Food by Blue Jays (Cyanocitta cristata)
Paul Alexander Callo and Curtis S. Adkisson
Department of Biology, Virginia Tech, Blacksburg, VA 24060
Blue jays (Cyanocitta cristata) are important dispersers of Quercus, Fagus, and Castanea nuts in eastern North America and their caching behavior in the wild has been well documented. Unlike in other Corvid species such as Clark's nutcrackers, pinyon jays, and western scrub-jays, the cache recovery behavior of blue jays has not been well studied. A laboratory study was conducted in which the caching and recovery behaviors of blue jays were examined. The performance of caching birds was quantified and compared with a random foraging model. Blue jays do return to their own caches with success rates higher than predicted by a random searching model, and they probe fewer sites than predicted by a random searching model. They cache significantly more caches near edges and objects than expected in the laboratory environment, but they do not recover more of these edge caches than expected by random. The possible role of other hypothesized recovery mechanisms is also discussed.
Key words: Blue jay; Cyanocitta cristata; Caching; Recovery behavior
Variation in the Bout Structure of Northern Mockingbird (Mimus polyglottus) Singing
Nicholas S. Thompson,1 Emily Abbey,1 Jessica Wapner,1 Cheryl Logan,2 Peter G. Merritt,3 and Albert Pooth4
1Departments of Biology and Psychology, Clark University,
2Department of Psychology, University of North Carolina, Greensboro, NC
3Treasure Coast Regional Planning Council, Stuart, FL
4Department of Biology, University of Miami, Miami, FL
The highly variable singing of the northern mockingbird (Mimus polyglottus) is distinguishable from that of other sympatric mimids by its organization into bouts: the bird's tendency to repeat an element several times before proceeding to another. To determine the degree to which this bout structure is a common feature of mockingbird song, 10 samples of singing from widely different populations and circumstances were examined including examples from coastal and central New England, central North Carolina, and the Florida peninsula and examples of day and night and spring and summer song. Measures included note parameters (peak frequency, internote interval, and note duration) and bout parameters (songs per bout and mean values of note parameters). All samples were found to be organized in bouts, but the degree of differentiation of the bouts (i.e., the degree to which the boundaries between bouts were emphasized by the contrast between their songs) varied both within and between samples. Bout differentiation was not maximized: songs of bouts sung in close temporal proximity were more similar than average, and the performance overall seemed to consist of runs of high and low values of note and/or bout parameters. Whether these variations in the bout structure reflect changes in the state of the singer or in his circumstances or serve to enhance the overall effectiveness of his performance remains to be determined.
Key words: Mimidae; Mockingbird; Communication; Song variation; Song structure
Nest Site Selection in Monk Parakeets (Myiopsitta monachus) in Florida
Joanna Burger1 and Michael Gochfeld2
1Division of Life Sciences, Rutgers University, Piscataway,
2Environmental and Community Medicine, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854
Monk parakeets (Myiopsitta monachus) have been expanding their range in Europe and North America. We examined their nest site selection in two colonies in South Florida to test the hypothesis that they select specific size and species of tree for their nests, and place the nest and its opening away from the prevailing winds from the Atlantic Ocean. They selected nest trees as a function of species and size of the tree. All of the nests at Miami Springs were in punk trees (Melaleuca quinquenervia), and all the nests in Bryant Park were in coconut palm (Cocos nucifera) trees, even though there were a variety of other trees present. At both colonies they nested in taller trees than were generally available. At Bryant Park they nested in trees that had significantly larger diameter-at-breast-height than the trees that were available, although this was not the case at Miami Springs. The nests were either among the coconuts or at the distal ends of the Melaleuca branches, and away from the prevailing winds. We suggest that the location of nests reflects selection for strong, large trees, and the relative smallness of the nests in comparison with those in their native South America may partially reflect pressures from high storm winds.
Key words: Monk parakeet; Myiopsitta monachus; Nest site
selection; Invasive species; Florida