|ognizant Communication Corporation|
VOLUME 15, NUMBER 1
Bird Behavior, Vol. 15, pp. 1-10
1056-1383/02 $20.00 + .00
Copyright © 2002 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.
Development of Feeding Mechanics in Growing Birds: Scything Behavior in Juvenile American Avocets (Recurvirostra americana)
M. Becker, M. A. Rubega, and L. W. Oring
Department of Environmental and Resource Sciences, University of Nevada, Reno, NV
American avocets (Recurvirostra americana) exhibit a distinctive and rare feeding behavior known as scything, in which the partially opened beak is swept from side to side through the water column. The behavior has been described in detail for adults, but the form and frequency of its use was heretofore unexamined in the precocial, self-feeding hatchlings of this species. We examined the development of scything in the period from hatching to just before fledging via observations of free-living chicks. We found that avocet chicks exhibit three distinct forms of the behavior, which disappear or are acquired with age. The change in behaviors is gradual, and the stages of development overlap, both within and among individuals. The frequency of scything as a feeding behavior increases with age, until it becomes the dominant feeding behavior just prior to fledging. The variation in scything behavior documented in this and other studies suggests that mastery of scything requires a substantial repertoire of motor patterns, and the time required to fully develop or learn that repertoire may be considerable.
Key words: American avocet; Feeding; Scythe; Behavioral development
Alarm Calling and Predator Discrimination in the Arabian Babbler (Turdoides squamiceps)
Jonathan V. Regosin
Department of Biology, University of Pennsylvania, 415 South University Avenue, Philadelphia, PA 19104
Cooperatively breeding Arabian babblers (Turdoides squamiceps) used three distinct classes of alarm call in response to potential predators: "pshews," "tsits," and "trills." Pshews were associated with flying avian predators and escape behavior, tsits were associated with terrestrial predators and approach-mobbing behavior, and trills were associated with perched avian predators and monitoring behavior. In response to perched avian predators, however, trills were often combined with tsits or pshews and tsits (66.7% of observed cases). The observed pattern of mixed calling in response to perched avian predators suggests that babbler alarm calls may sometimes lack the stimulus specificity of externally referential signals. Alternative hypotheses are discussed.
Key words: Alarm calling; Predator discrimination; Referent; Cooperative breeding
Selection of Red-Winged Blackbird (Agelaius phoeniceus) Hosts by the Brown-Headed Cowbird (Molothrus ater)
Naomi D. Grant1 and Spencer G. Sealy2
1Department of Biology, Laurentian University, Sudbury, Ontario,
Canada P3E 2C6
2Department of Zoology, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
Brood parasitism is a reproductive strategy in which the female lays her eggs in the nests of other birds, the hosts. If host use is largely nondiscriminatory ("shotgun parasitism"), any available nest is parasitized once broad requirements have been met. On the other hand, if host selection is based on a cost-benefit trade-off, brood parasites should discriminate among potential hosts and select the most suitable. We refer to this as the host quality hypothesis. We examined the host quality hypothesis within a red-winged blackbird (Agelaius phoeniceus) population at Delta Marsh, Manitoba. We predicted that primary red-winged blackbird females would be parasitized more frequently than females of lower status, and that both cowbird and redwing nestlings would be more successful in nests tended by primary females. Indeed, we found a higher frequency of cowbird parasitism among primary redwing females than among lower-status females. Cowbird nestlings in the care of primary redwing females grew less variably, and nestlings of primary females grew more rapidly than those of secondary females.
Key words: Brood parasitism; Host quality; Red-winged blackbird;