Volume 45, Number 2, December 1998:
Feral Pigeons

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ABOUT THIS ISSUE
- about KSN
- about the author

IN THIS ISSUE
- introduction
- origin of feral pigeons
- basic plumages
- mate choice and plumages
- advantages of different plumages
- advantages of choosing different mates
- breeding seasons
- reproducative data
- brood reduction
- living in colonies
- commuter pigeons
- relationships with people
- reference

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Updated: March 9, 2005
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Feral Pigeons
by Richard F. Johnston

ADVANTAGES OF CHOOSING DIFFERENT MATES

Since random mate choice would select for similar neighbors, nonrandom mate choice in pigeons causes outcrossing. Among other things, it tends to maintain a diverse set of plumages. Perhaps as a result, feral pigeon populations show reasonably stable plumage variation. This disassortative mate choice would effectively maintain plumage variation whether or not escapes from captivity brought a variety of colors and patterns into a population. If for any reason the frequency of one form should decline, its value in mate choice would increase, resulting in frequency-dependent selection. This generates slowly fluctuating frequencies of forms in populations, creating a balance in variation through time.

Outbreeding or outcrossing resulting from disassortative mating generates what has been called hybrid vigor or "heterosis." The term "hybrid vigor" was in use by animal breeders as long ago as the 18th-century. Outbreeding causing multilocus heterosis [a variety of genes at many chromosomal locations] is known as a source of vigorous domestic stock having rapid embryonic growth with development generally free from structural defects. There is no reason to suppose feral populations are dissimilar in any fundamental way; they too should benefit from this genetic variation.

A simple test for multilocus heterosis results from the prediction that character variability will be low in genetically variable (heterozygous) versus more nearly invariable (homozygous) individuals from a population. In a study at the University of Kansas, sixty-four North American feral pigeons examined at 49 enzyme loci were separated into groups of high and low heterozygosity and the lengths of eight appendicular skeletal elements were taken for analysis. Bones proved to be larger in the birds with high genetic heterozygosity and, most importantly, all eight elements of these birds were significantly less variable than those from the group of low genetic heterozygosity. A permissible conclusion is that the developmental pathways of the heterozygous birds were better buffered against outside environmental influences, thus avoiding possible induced developmental problems, such as left-right asymmetry.

A dramatic example of the effect of single-locus (one gene) heterozygosity or reproductive and survival fitness is drawn from J. Felinger's work on pigeon transferrins. Transferrins are bacteriostatic and fungistatic proteins important in vertebrate immune systems. Young pigeons, while in the egg and for more than a week after hatching, are incapable of producing their own transferrins. But transferrins of their mothers are provided in egg yolk and egg albumin. Sixty-six percent of the eggs of transferrin heterozygous mothers hatched, while mothers of one transferrin homozygote hatched 52 percent, and of the other 48 percent, showing a highly significant reproductive advantage for heterozygous females. Thus, prospects for survival of squabs and reproduction by adult females were obviously affected by genetic variability.