Biology ETDs

Publication Date

5-2-1978

Abstract

Clark's Nutcrackers (Nucifraga columbiana) rely heavily on seeds of pinon pine (Pinus edulis) as a winter food supply in years of good seed production. During late summer and autumn these birds spend considerable time and energy harvesting seeds from green, unopened cones. I tested abilities of three groups of wild-caught birds to discriminate cone quality: (1) adults, (2) experiences juveniles, and (3) naive juveniles. The birds were given choice tests with two cones, three cones, and cones that had been painted. Under controlled conditions nutcrackers discriminated between cones of differing quality. Adults assessed cones more accurately than did juveniles in two-cone tests. Alteration of cone color affected the assessment ability of two adults and one juvenile. In three-cone tests, captive birds did not choose cones in order of decreasing quality. Primary cues used in discriminating between cones varied from bird to bird. Tactile cues, such as density and weight, appear to be especially important in the first several tests. Cone length, shape, width, and volume are highly correlated with density and weight and may be important in assessing cone quality, since most of the time the birds did not touch the cones before making a choice. Adults and experiences juveniles responded immediately to cones. One naïve juvenile never showed interest in cones and the other juvenile showed no interest until it observed an adult removing seeds from them, suggesting that recognition and assessment of cone quality is learned. Adult nutcrackers were more efficient in removing seeds, in terms of time and energy spent than experienced juveniles, which, in turn, were more efficient than the naive bird.

Language

English

Document Type

Thesis

Degree Name

Biology

Level of Degree

Masters

Department Name

UNM Biology Department

First Committee Member (Chair)

J. David Ligon

Second Committee Member

James Smith Findley

Third Committee Member

Albert Randolph Thornhill

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