|ognizant Communication Corporation|
VOLUME 12, NUMBER 1/2, 1997
Bird Behavior, Vol. 12, pp. 1-6, 1997
1056-1383/97 $10.00 + .00
Copyright © 1997 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.
Fledgling Age Affects Female Reactions to Mate Song in Free-living Northern Mockingbirds (Mimus polyglottos)
Cheryl A. Logan1 and Beth A. Donaghey2
1Psychology and Biology Departments, University of North
Carolina at Greensboro
2Psychology Department, Emory University
The responses of mated female northern mockingbirds to their mates' songs, to strange mockingbird song, and to brown thrasher song were tested with fledglings of varying ages present on territory. Males who had resumed singing in preparation for a subsequent brood were temporarily removed from their territories, and females were tested with no male present. When responses were compared against a baseline measured just prior to playback, females showed evidence of responding to both mate and strange mockingbird song, but not to control brown thrasher song. In addition, two measures of females' reactions to their mates' songs were positively associated with fledgling age. As fledgling age increased, so did time spent near the speaker playing mate song and the number of approaches to the song. However, no variation in response to stranger or brown thrasher song was associated with the age of dependent young, though there were trends indicating a negative correlation between fledgling age and latency to approach both mate and strange mockingbird song. Females' species-specific response to song confirms other work indicating that males direct their songs to females. In addition, these data indicate that fledgling age affects females' reactions to male song. They suggest that the effect of fledgling age on renesting intervals in double and multiple brooded species may be mediated in part by the impact of fledgling age on females' reactions to male vocal signals.
Key Words: Song playback; Female songbirds; Fledgling age; Northern mockingbird
Multistage Scatter-Hoarding Decisions in the Gray Jay (Perisoreus canadensis)
Thomas A. Waite1 and John D. Reeve2
1Department of Zoology, Ohio State University, Columbus,
2Southern Forest Experiment Station, USDA Forest Service, P.O. Box 5500, Pineville, LA 71360
Animals storing food in scattered sites are assumed to accrue greater fitness gains if their decisions ultimately lead to higher net rates of energy intake during cache retrieval. However, because cache survival is density dependent, maximizing the gross rate of hoarding will fail to meet this criterion. Storing all items near a point source will yield a high hoarding rate but loss due to theft may be quite high as well. Conversely, storing all items at distant, widely scattered sites will yield a low theft rate but also a low hoarding rate. Scatter-hoarders are thus expected to balance these conflicting forces. We investigated the behavior of gray jays (Perisoreus canadensis) exploiting experimental food sources at some distance from the forest (where all hoarding occurs). Contrary to the prediction of a rate-maximization model, the jays spaced their caches less widely when they exploited a distant source than when they exploited a source on the edge of the forest. Redistribution of caches by the hoarders may account for this contradiction of the model, which implicitly assumes no such recaching. Jays exploiting distant ephemeral sources could achieve a high rate of storage by temporarily concentrating their caches in trees along the edge of the forest. Later, they could reduce the vulnerability of the caches by moving some of them to widely scattered sites. A follow-up study showed that gray jays hoard in this two-stage manner when they exploit distant sources. Rapid sequestering and subsequent recaching thus appear to be key components of a dynamic scatter-hoarding strategy.
Key Words: Caching; Decision making; Hoarding; Rate maximizing
Discrimination Among Natural and Altered Zebra Finch (Taeniopygia guttata) Motifs: A Comparative Study
Amy A. Nespor and Robert J. Dooling
Department of Psychology, University of Maryland
The present study was undertaken to provide comparative data on the perception of complex bird vocalizations. The ability to discriminate among natural and altered species-specific zebra finch song motifs was measured in zebra finches (Taeniopygia guttata), budgerigars (Melopsittacus undulatus), and humans (Homo sapiens). Birds were trained and tested using an operant conditioning paradigm whereas humans were given general instructions and tested with the same procedure. Subjects were tested on their ability to discriminate among a number of synthetic vocal sets, including syllable transpositions, reversals, deletions, and doublings. In addition, the ability to discriminate small changes in syllable intensity and intersyllable duration was measured. Zebra finches and budgerigars performed better than humans on most discriminations. However, humans performed better than birds in discriminating motifs in which syllables were doubled. These results show differences in the perception of zebra finch songs between humans and birds that appear to be counterintuitive.
Key Words: Perception; Song syllables; Birds; Hearing; Zebra finches; Operant conditioning
Sharply Timed Behavioral Changes During the First 5 Weeks of Life in the Domestic Chick (Gallus gallus)
G. Vallortigara,1 R. J. Andrew,2 L. Sertori,3 and L. Regolin3
1Dipartimento di Scienze Filosofiche e Storico-Sociali, Laboratorio
di Psicologia Sperimentale, Università di Udine, 33100 Udine, Italy
2Sussex Centre for Neuroscience, School of Biology, Sussex University, Brighton BN1 9QG, UK
3Dipartimento di Psicologia Generale, Università di Padova, 35131 Padova, Italy
Chicks reared by a broody hen were studied under seminatural conditions up to day 37 of life. A number of sharply timed points of change in the occurrence of certain behaviors was observed. These points were characterized by the presence of a period in which the occurrence of a particular behavior increased and then declined again sharply, so that explanation by a progressive maturation as part of development is unlikely. In the first 15 days, these periods corresponded remarkably to those revealed in a previous study by Workman and Andrew, centered at around day 8 and day 11, and associated by these authors with age-dependent shifts in lateralization of function in the central nervous system. Further periods were identified at later ages, in particular day 14 and day 36, which showed striking synchrony in their appearance in chicks studied in very different environmental conditions, and that are here tentatively attributed to the development of brain lateralization as well.
Key Words: Development; Lateralization; Chick; Gallus gallus
Social Foraging of the Forktailed Drongo Dicrurus adsimilis: Beater Effect or Kleptoparasitism?
Marc Herremans and Diane Herremans-Tonnoeyr
Department of Wildlife and National Parks, Botswana
Previous studies on mixed-species insectivorous bird flocks argued that kleptoparasitism was the main advantage of social foraging to forktailed drongos. The present study found that commensal association of forktailed drongos with prey beaters was widespread in Botswana (635 of 4633 birds observed), particularly in winter, during inclement weather, and in the cold morning hours. Associations with livestock accounted for 61% of cases; forktailed drongos foraged in the company of terrestrially foraging birds in 71% of 248 cases of association with wildlife species (37 species in total). Association with nonterrestrial insectivorous birds only constituted 4% of all cases. Only seven forktailed drongos were observed to behave indirectly kleptoparasitically: all corrupted their vigilant function in mixed-species bird flocks by using alarm calls to distract insectivorous birds at the crucial moment of prey detection. A single case of silent, direct kleptoparasitism was recorded. Kleptoparasitism occurred only during drought, or exceptionally cold weather, when abundance of flying insect prey was low, indicating a high threshold for interspecific kleptoparasitic behavior.
Key Words: Beaters; Kleptoparasitism; Forktailed drongo; Dicrurus adsimilis; Botswana
Allocation of Parental Duties and Foraging Behavior Influence Body Condition of Adult Common Terns, Sterna hirundo
Institut für Vogelforschung "Vogelwarte Helgoland," An der Vogelwarte 21, D-26386 Wilhelmshaven, Germany
Body mass development of common terns (Sterna hirundo) was investigated in relation to foraging strategies and the allocation of parental duties during incubation and chick-rearing. Decreasing body mass of incubating females foraging in tidally influenced marine areas was related to time constraints due to incubation and fluctuations in prey availability. In contrast, body mass of females specializing on limnetic prey (three-spined stickleback, Gasterosteus aculeatus) around the colony was not affected. Body mass was further affected by parental duties at the onset of chick-rearing. During the first week of chick-rearing the mates showed different behavioral patterns: males fed more frequently than females, which in turn spent more time brooding, thereby reducing the time for their own food intake. Females fed sticklebacks from limnetic areas more often than did males. However, as small chicks prefer larval fish and small marine prey instead of sticklebacks, all females were forced to forage in marine areas. The resulting constraints caused significant mass decreases in females at the onset of chick-rearing. In males, only the body mass of individuals that specialized in foraging on sticklebacks decreased significantly, indicating difficulties in finding suitable prey for their chicks.
Key Words: Common tern; Sterna hirundo; Body condition;
Foraging behavior; Parental care