ognizant Communication Corporation


VOLUME 12, NUMBER 3/4 1998

Bird Behavior, Vol. 12, pp. 57-66, 1998
1056-1383/98 $10.00 + .00
Copyright © 1998 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Yellow Warblers (Dendroica petechia) Do Not Recognize Their Own Eggs

Spencer G. Sealy and Janice C. Lorenzana

Department of Zoology, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

Early in the laying cycle and nesting season, many yellow warblers (Dendroica petechia) bury clutches that have been parasitized by brown-headed cowbirds (Molothrus ater). This behavior indicates that yellow warblers are able to determine that they have been parasitized; however, the stimulus for burial of cowbird eggs remains unknown. Four experiments were done at 114 yellow warbler nests to determine whether the cue that elicits burial is the recognition of a foreign, nonmimetic egg in yellow warbler nests. To recognize the presence of a nonmimetic egg, a yellow warbler must be able to recognize its own eggs. We were not able to elicit burial with any of our clutch manipulations. Yellow warblers accepted nonmimetic undersized eggs that presumably would be easier to eject than cowbird eggs. They also accepted clutches composed entirely of cowbird eggs and clutches of cowbird eggs and one of their own eggs. Nest watches revealed that female warblers do not significantly change their behavior upon their return to a nest that has been parasitized recently with a cowbird egg. In our fourth set of experiments, we observed that yellow warblers visually cue into broken eggs and immediately eject the broken egg, without settling on the clutch. Yellow warblers can lift simulated broken cowbird eggs, but only when a piece of shell is affixed to the cowbird egg. This is interesting given that the addition of unbroken cowbird eggs did not elicit any visual reaction from the warblers, despite the considerable difference in size and appearance of cowbird and yellow warbler eggs. This provides strong support that yellow warblers do not know the appearance of their own eggs and, hence, do not recognize a cowbird egg as being different. They do, however, cue into eggs with broken edges and eject them.

Key words: Yellow warblers; Egg recognition; Brood parasitism; Brown-headed cowbirds

Address correspondence to Spencer G. Sealy, Department of Zoology, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada. E-mail: sgsealy@cc.umanitoba.ca

Bird Behavior, Vol. 12, pp. 67-70, 1998
1056-1383/98 $10.00 + .00
Copyright © 1998 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Red-Winged Blackbirds (Agelaius phoeniceus) Accept Prematurely Hatching Brown-Headed Cowbirds (Molothrus ater)

D. Glen McMaster and Spencer G. Sealy

Department of Zoology, University of Manitoba, Winnipeg, MB R3T 2N2 Canada

Red-winged blackbirds (Agelaius phoeniceus) eject simulated broken eggs from their nests at a high frequency during the incubation period. However, the frequency of ejection of simulated broken eggs declines abruptly beginning the day before blackbird clutches hatch, perhaps to ensure parent birds do not mistake their own pipped eggs for broken ones and eject them. We tested whether blackbirds accept hatching eggs during the incubation period. We added brown-headed cowbird (Molothrus ater) eggs that were close to hatching to blackbird clutches that were midway through incubation, and predicted that blackbirds would eject hatching cowbird eggs. Red-winged blackbirds did not eject cowbird eggs that hatched midway through incubation. We conclude parent birds perceive hatching eggs to be different from broken eggs. The decline in the ejection frequency of simulated broken eggs just before hatching may function during hatching to prevent parent birds from removing egg shells that hatchlings have not yet extricated themselves. Further experiments are required to demonstrate how stimuli from hatching eggs suppress egg ejection behavior.

Key words: Red-winged blackbirds; Brown-headed cowbirds; Egg ejection; Hatching

Address correspondence to D. Glen McMaster, Saskatachewan Wetland Conservation Corporation, 202-2050 Cornwall St., Regina, SK S4P 2K5, Canada. E-mail: GMMASTER@WETLAND.SK.CA

Bird Behavior, Vol. 12, pp. 71-78, 1998
1056-1383/98 $10.00 + .00
Copyright © 1998 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Responses of Nesting Song Sparrows (Melospiza melodia) and Red-Winged Blackbirds (Agelaius phoeniceus) to Models of Parasitic Cowbirds and Nonthreatening Towhees

Bill M. Strausberger and Matthew E. Horning

Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607

Many studies have compared nest defense elicited by models of brood parasites and innocuous species placed near potential host nests. Because the majority of costs associated with brood parasitism are incurred in the nest, it may be more appropriate to conduct such experiments at nests unless hosts respond to all intruders at their nests as enemies. We found that nesting species distinguish among threatening female brown-headed cowbirds (Molothrus ater) that frequently parasitize them, male cowbirds generally thought not to participate in parasitism, and innocuous eastern towhees (Pipilo erythrophthalmus). Taxidermic mounts of each were placed at the nests of two common host species: song sparrow (Melospiza melodia) and red-winged blackbird (Agelaius phoeniceus). Both host species reacted more aggressively toward female cowbird models than towhee models, whereas red-winged blackbirds also reacted more aggressively toward male cowbird models than toward towhees. These findings suggest that host species can discriminate between potentially threatening and nonthreatening intruders (both species and sex specific) at the nest; however, this discrimination may be imperfect as was indicated by red-winged blackbird's aggressive response toward male cowbirds. Alternatively, male cowbirds may be perceived as more of a threat to red-winged blackbirds than female towhees.

Key words: Brown-headed cowbird; Nest defense; Brood parasitism

Address correspondence to Bill M. Strausberger, Department of Biological sciences (M/C 066), University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 60607. E-mail: bstrau1@icarus.uic.edu

Bird Behavior, Vol. 12, p. 79-84, 1998
1056-1383/98 $10.00 + .00
Copyright © 1998 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Feeding Behavior in Steller's Jays (Cyanocitta stelleri): Effects of Food Type and Social Context

Marc Bekoff,1 Colin Allen,2 and Ann Wolfe3

1Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, CO 80309-0334
2Department of Philosophy, Texas A&M University, College Station, TX 77843-4237
3Department of Philosophy, University of Wisconsin, Madison, WI 53706

In this study we analyzed various factors affecting the activities in which Steller's jays (Cyanocitta stelleri) engaged while feeding. We found that the rate of pecking at seeds by jays was affected by available seed type and the presence and activity of nearby conspecifics. Jays at an artificial feeding platform seemed to pay attention to other individuals, in that they pecked at a lower rate when another jay was nearby, except when the other jay was feeding at a different platform. The decreased feeding rate when two jays shared the same feeding platform is contrary to the widely reported pattern of increased feeding and decreased scanning correlated with increased group size in various species. Our analysis suggests that this pattern of behavior fits with observations that Steller's jays show site-specific dominance, mutual interference at a concentrated food source, and do not live in structured flocks with consistent membership.

Key words: Steller's jay; Feeding behavior; Social vigilance; Social organization

Address correspondence to Dr. Marc Bekoff, Department of EPO Biology, University of Colorado, Boulder, Colorado 80309-0334. E-mail: marc.bekoff@colorado.edu

Bird Behavior, Vol. 12, pp. 85-90, 1998
1056-1383/98 $10.00 + .00
Copyright © 1998 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

The Effect of Heterospecifics on the Group-Size Effect in White-Crowned Sparrows (Zonotrichia leucophrys)

Thomas J. Valone and Amber J. Wheelbarger

Department of Biology and Center for the Study of Biodiversity, California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330-8303

We examined patterns of vigilance in white-crowned sparrows (Zonotrichia leucophrys) to determine how the presence of heterospecific California towhees (Pipilo crissalis) affected scanning behavior. White-crowned sparrows fed at an artificial food patch in small flocks both in single-species flocks and with towhees. Mean per capita scan durations of white-crowned sparrows in single-species flocks declined significantly with increasing group size (i.e., they exhibited the group-size effect). Scan durations did not decline as flock size increased, however, when a single California towhee fed with the white-crowned sparrows, such that the group-size effect was not apparent. These results add to the growing list of cases suggesting that individuals are vigilant not solely to acquire information about predators; in this case, individual white-crowned sparrows, when feeding with a large heterospecific, appear also to attempt to acquire information about a potential aggressor while scanning their surroundings.

Key words: Vigilance; Group size; White-crowned sparrow; California towhee

Address correspondence to Thomas J. Valone, Department of Biology, California State University Northridge, Northridge, CA 91330-8303. E-mail: Thomas.Valone@csun.edu

Bird Behavior, Vol. 12, pp. 91-96, 1998
1056-1383/98 $10.00 + .00
Copyright © 1998 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.

Temporal Processing in Japanese Quail (Coturnix japonica)

Chana k. Akins, Derek D. Mace, and Philipp J. Kraemer

Department of Psychology, University of Kentucky, Lexington, KY 40506

Research on temporal processing in animals indicates that animals utilize temporal information in their environment to perform such behaviors as migration and foraging. Comparative studies suggest that a variety of mammalian and bird species are sensitive to scheduled events. Timing and the capacity for working memory have been well-documented in pigeons and rats. However, establishing generality of such processes requires studying other species. Japanese quail are a gallinaceous species of bird that are easy to maintain in the laboratory. The purpose of the present experiment was to investigate timing and working memory in Japanese quail. A duration estimation procedure was used in which quail subjects were presented with a sample stimulus (amber-colored keylight) for 2 or 10 s followed by presentation of a pair of choice stimuli (red and green keylights). Matching the sample with the correct choice stimulus resulted in food reinforcement. Once subjects could accurately match the sample with the correct choice stimulus, timing was assessed by testing subjects with intervening duration samples that ranged between the two sample durations. Results showed that subjects accurately matched test duration samples with previously trained duration samples of similar length. However, when a delay interval was inserted between the offset of a duration sample and presentation of the choice stimuli, matching accuracy decreased and subjects chose the choice stimulus associated with shorter duration samples over the choice stimulus associated with long durations samples. The assumption of this ``choose-short'' effect is that the delay interval makes the long sample duration appear shorter than it actually is. This ``choose-short'' response bias is a highly replicated finding in pigeons and rats, and is a widely studied phenomenon in cognitive animal research. The present findings provide evidence for timing in Japanese quail, suggest that the working memory capacity of quail and pigeons is similar, and provide evidence for the generality of temporal processes across species.

Key words: Japanese quail; Timing; Memory; Cognition

Chana K. Akins, Department of Psychology, University of Kentucky, Lexington, KY 40506-0044. E-mail: CKAKIN1@POP. UKY.EDU