Date of Award:

5-1982

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Department name when degree awarded

Fisheries and Wildlife

Committee Chair(s)

John A. Kadlec

Committee

John A. Kadlec

Committee

David F. Balph

Committee

Martha H. Balph

Committee

Keith L. Dixon

Committee

Ivan G. Palmblad

Committee

Frederick G. Lindzey

Abstract

This study examined the influence of winter social behavior, particularly dominance relationships, on the subsequent nesting habitat selection and reproductive success of Black-billed Magpies (Pica pica hudsonia) on 2 areas in northern Utah. Hierarchical cluster analysis ordinated the habitats available to breeding birds and Chi-square and Bonferoni-z statistics were used to determine those habitat types the magpies seemed to prefer. Social status was determined by observing color-banded birds engaged in agonistic encounters at winter bait stations. Social dominance was evaluated by % dyads won, not by total % victories. Relationships between winter social status of magpies and their subsequent breeding habitat use and reproductive performance was tested by Kendall's Tau.

Winter foraging flocks were comprised primarily of juvenile (1st year) birds while adults tended to remain as isolates or in pairs. Social status within flocks was correlated with age and sex; males dominated females and juvenile males dominated adult males. This was caused by differences in the social organization of adults and juveniles which created asymmetric views of winter food resources between male age classes.

Breeding territories were densely packed in all habitats with a mean size of 0.5 ha. Date of clutch initiation was significantly correlated with clutch size and number of fledglings, with earlier nests more successful. Juveniles occupied marginal habitats and produced fewer offspring than adults.

Within a dominance hierarchy of juvenile males, no significant differences in reproductive variables were detected except date of clutch initiation and weight of nestlings. Nestlings of dominant parents fledged earlier and were heavier than those of subordinates, which should increase post-fledging survival. This study has documented, for the first time in a free-living population, relationships between characteristics of nestlings and their future dominance status. Two characteristics, fledging date and rank (by weight) in the brood, were correlated with future winter dominance of juvenile males. The dominance status of male magpies is associated with many factors related to relative fitness, with hereditary components moderated by environmental and social factors.

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