Biology ETDs

Joe Haydock

Publication Date

12-28-1984

Abstract

Hypotheses concerning the adaptive significance of asynchronous hatching in relation to brood reduction were tested using experimental manipulations of brood of Chihuahuan Ravens (Corvus cryptoleucus) in southeastern New Mexico in 1981 and 1982. Additionally, in 1978 and 1979, breeding success was monitored at the study site. Several types of experimental manipulations, including the following, were performed on newly hatched nestlings: (1) The largest nestling in a nest was transferred to another nest were it was approximately equal in weight to the smallest nestling (runt) in that nest. (2) The smallest nestling of a nest was transferred to another nest where it was approximately equal in weight to the largest nestling in that nest. (3) Nestlings were exchanged between nests (that originally contained five or six eggs) to obtain nests with five or six nearly equal-sized nestlings. In control nests, the most productive clutch size was larger than the most common clutch size. Growth rates and weights for nestlings that fledged were similar in most cases, regardless of clutch size or hatch position. Fledging success was significantly higher in the experimental broods with equal-sized nestlings than in the control nests in which six young hatched in 1981. However, in 1982, fledging success was nearly equal in the experimental and control nests. Although growth rates were not significantly lower, fledging weights were significantly lower in the experimental broods with equal-sized nestlings. Runts transferred to a largest nestling position in another nest nest fledged as well as the largest nestlings in control nests. Largest nestlings transferred to a runt position fledged as rarely as runt nestlings in control nests. Lack's hypothesis that asynchronous hatching allows for adjustment brood size is supported. However, several other factors must also be considered to explain fully clutch size and degree of asynchronous hatching found in Chihuahuan Ravens.

Project Sponsors

Sandia Laboratories and Westinghouse Corporation contracts to J. D. Ligon

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

William R. Rice

Third Committee Member

Manuel C. Molles

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