|ognizant Communication Corporation|
VOLUME 13, NUMBER 1, 1999
Bird Behavior, Vol. 13, pp. 1-7, 1999
1056-1383/99 $10.00 + .00
Copyright © 1999 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.
Aggressive Responses of Red-Winged Blackbirds (Agelaius phoeniceus) Toward Brown-Headed Cowbirds (Molothrus ater) in Areas of Recent and Long-Term Sympatry
John W. Prather,1 Catherine P. Ortega,2 and Alexander Cruz1
1Department of Environmental, Population, and Organismic
Biology, University of Colorado, Boulder, CO 80309-0334
2Biology Department, Fort Lewis College, Durango, CO 81301-3999
A comparative study of the relative aggression of red-winged blackbirds (Agelaius phoeniceus) toward mounted female brown-headed cowbird (Molothrus ater) and control mounts placed in life-like positions 1 m from their nests in an area of recent (Florida) and historical sympatry (Colorado) was undertaken. We predicted that Florida red-winged blackbirds would not recognize cowbirds as a potential threat and would respond less aggressively toward a mounted female cowbird near their nests than red-winged blackbirds in Colorado, where cowbirds are known to parasitize blackbirds. Contrary to our prediction, red-winged blackbirds nesting in Florida (n = 15) and Colorado (n = 19) attacked mounted female cowbirds in nearly all trials, and there were no significant differences between populations in the amount of time spent aggressively responding to the cowbird mounts. Red-winged blackbirds from both areas physically attacked cowbird mounts significantly more often than female control mounts (eastern meadowlark Sturnella magna, western meadowlark S. neglecta, white-crowned sparrow Zonotrichia leucophrys, northern cardinal Cardinalis cardinalis) and spent significantly more time aggressively responding to cowbird mounts than control mounts. Both Colorado and Florida populations of the red-winged blackbird appear to recognize cowbirds as potential threats to their breeding success. The expression of antiparasite defenses by Florida populations suggests that these traits may be controlled genetically but persist in such areas through gene flow. An alternate possibility is that Florida red-winged blackbirds are simply more aggressive in the defense of their territories than red-winged blackbirds from Colorado. Unlike blackbirds in Colorado, Florida blackbirds rarely nest colonially. As only a few birds defend the territory, they may be especially diligent and aggressive in the defense of their nests.
Key Words: Brown-headed cowbird; Red-winged blackbird; Nest defense; Brood Parasitism
Discrimination of Gargle Calls by Black-Capped Chickadees (Poecile atricapillus)
Lori E. Miyasato and Myron C. Baker
Department of Biology, Colorado State University, Fort Collins, CO 8053
Gargle calls, vocalizations used by black-capped chickadees (Poecile atricapillus) during agonistic interactions, were shown previously to exhibit geographic dialect populations along a river drainage in northern Colorado, U.S. In this study, recordings of those gargle calls were used in a playback test to determine whether chickadees discriminate between gargles of different populations. Chickadees captured from three sites were tested individually in an aviary into which were broadcast gargles recorded either from birds of their own local population or birds from a distant population. A videotaped image of a gargling chickadee was simultaneously shown to the subjects. Response was measured as the total time spent avoiding the area of the aviary from which the audio and visual stimuli were broadcast. Combined data from all three sites showed that birds demonstrated a stronger avoidance response when played local calls than when played calls from a distant population.
Key Words: Playbacks; Vocalizations; Gargle calls; Chickadees; Geographic variation
Seasonal Variation in Hatching Spreads in Mountain Bluebirds (Sialia currucoides): A Test of the Nest Failure Hypothesis
Percy N. Hebért
Department of Zoology, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2
The purpose of this study was to examine the importance of the nest failure hypothesis in explaining the evolution o hatching synchrony in mountain bluebirds (Sialia currucoides). The nest failure hypothesis argues that intraclutch hatching intervals are an adaptive response to the ratio of the risk of total nest failure due to predation during the fledging period relative to that during the laying period. Daily survival probabilities (DSP) of nests were determined from data collected during regular nest visits throughout the nesting cycle. The DSP of nests was similar between the laying and fledging period for both first and second broods. Also DSP values for the laying and fledging periods did not differ between first and second broods. Expected productivity ratios, derived from the nest failure model, were greatest when incubation began with the laying of the first egg. Observed hatching spreads, however, indicated that females tending first clutches delayed incubation at least until clutch completion, whereas females tending second clutches delayed incubation until the penultimate egg was laid. Thus, hatching spreads in first and second clutches were significantly less asynchronous than predicted by the nest failure hypothesis. The results of this study indicate that temporal variations in the risk of predation have probably not played a significant role in the evolution of hatching synchrony in mountain bluebirds.
Key Words: Mountain bluebird; Sialia currucoides; Total
nest failure; Hatch spreads
Role of Human Disturbance in Response Behavior of Laysan Albatrosses (Diomedea immutabilis)
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
Laysan albatrosses (Diomedea immutabilis) nest on Midway Atoll, which was historically devoid of mammalian predators. They therefore exhibit few antipredator behaviors. The importance of the degree of prior exposure to human disturbance as an influence on response behavior was examined using an approaching person as the stimulus. Both the prior disturbance and the type of approach (direct or tangential), as well as their interaction, influenced how soon and how strongly the albatrosses responded. Albatrosses that had experienced very little prior human exposure responded sooner and more severely than did those that were frequently exposed to humans. These experiments suggest that albatrosses can habituate to the presence of humans, and that human exposure should be limited to confined areas, rather than distributing human activities throughout the colony. Maintaining some areas for ecotourism (accepting the consequences of disturbance) and restricting access to other areas, appears to be a sound management strategy. The impact of disturbance on survival remains to be studied.
Key Words: Habituation; Human disturbance; Albatross; Approach distance
Head Movement and Vision in Underwater-Feeding Birds of Stream, Lake, and Seashore
Lee W. Casperson
The Rochester Theory Center for Optical Science and Engineering and The Institute of Optics, University of Rochester, Rochester, NY 1467-0186
Water-associated birds face special challenges in dealing with their two worlds of air and water. This study considers as a class those birds that seem to plan their underwater foraging from a wading or above-water perched position. A vertical bobbing motion of the head is particularly common among these birds, and the somewhat diffuse literature on this subject is reviewed and correlated. The vertical head movement may aid a bird in acquiring visual information through the interference and distortion caused by reflection and refraction at the air/water boundary.
Key Words: Vision; Head movement; Underwater feeding; Bobbing
The Influence of Social Context on the Vocalizations of Mallard Ducklings (Anas platyrhynchos)
Gloria M. Hicinbothom and David B. Miller
Department of Psychology, University of Connecticut, Storrs, CT 0669
Acoustic properties of mallard duckling (Anas platyrhynchos) vocalizations differ based on the social context of the duckling. Vocalizations from 18 broods of socially reared, maternally naive mallard ducklings were recorded across four contexts that varied in the type of contact (visual, auditory, and tactile) between the focal duckling and its broodmates. The laboratory recording contexts included a brooder, an open field arena, as well as transparent and opaque barriers in a small pond. Additional vocalizations from field tapes of three broods of ducklings were included in the discriminant analyses. Vocalizations in contexts where the focal duckling is visually isolated from broodmates contain more notes per call, have higher dominant frequencies, have a slower repetition rate, and have longer note duration than the vocalizations in contexts where visual contact with siblings is maintained. These findings are important because repetition rate is the key acoustic property for mother-offspring communication. Ducklings respond differentially to maternal assembly calls than to maternal alarm calls with repetition rate being the salient difference between these two types of maternal calls. Ducklings vocalized significantly more in the opaque barrier and arena contexts (average of 94 and 18 notes per minute, respectively) where they were visually isolated from broodmates, than when they maintained visual contact with siblings in the transparent barrier context (average of 9 notes per minute). Although previous reports in the literature indicate that tactile contact is necessary for the induction of malleability in duckling visual and auditory preferences, our study indicates that this does not appear to be the case with respect to plasticity of vocal output.
Key Words: Mallard ducklings; Context; Vocalizations; Acoustic