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The Advantages of, and Constraints Forcing, Mate Fidelity in Pinyon Jays

John M. Marzluff and Russell P. Balda
The Auk
Vol. 105, No. 2 (Apr., 1988), pp. 286-295
DOI: 10.2307/4087492
Stable URL: http://www.jstor.org/stable/4087492
Page Count: 10
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The Advantages of, and Constraints Forcing, Mate Fidelity in Pinyon Jays
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Abstract

Pinyon Jays (Gymnorhinus cyanocephalus) live in flocks composed primarily of pairs and their offspring. We describe characteristics of 107 pair bonds. Pair bonds appear to be monogamous, perennial, and last an average of 2.5 yr. Males average 1.63 mates/lifetime, and females average 1.43. Males initiate breeding at an average of 2 yr, and females at an average age of 1.56 yr. Initial bonds formed between morphologically similar jays lasted significantly longer than those formed between disparate-size jays. Pairs had emergent properties that could not be accounted for by considering only properties of the mated individuals. Annual reproductive productivity did not vary significantly with duration of pair bonds. We found two cases of mate desertion; all other bonds were broken by deaths of partners. Previously successful jays remated with other successful birds, and unsuccessful birds remated with other unsuccessful birds, more often than expected by chance. Monogamy may have evolved because deserted females are incapable of rearing offspring, sex ratios are male biased, females are aggressive, and lifespan is long. Perennial pair bonds may have been imposed by social constraints more than favored by reproductive advantages. Three possible constraints were that previously unsuccessful individuals rarely mated with previously successful ones, that mates associated throughout the year, and that cooperation among group members may not have been maintained without long-term pair bonds between members of different extended families.

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