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Territoriality in the Purple Martin
Charles R. Brown
The Wilson Bulletin
Vol. 91, No. 4 (Dec., 1979), pp. 583-591
Published by: Wilson Ornithological Society
Stable URL: http://www.jstor.org/stable/4161272
Page Count: 9
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Territoriality in Purple Martins in north-central Texas was studied at 2 martin colonies. Two types of territory were distinguished: maximum--the number of rooms males claimed upon their arrival at the colony; and minimum--the number of rooms males claimed at the end of the season. Maximum territories were larger than minimum ones; males arriving in February and March claimed larger maximum territories than males that arrived in April and May. Territory in females closely paralleled territory in males. Unpublished studies suggested that polygyny occurred in about 5% of male Purple Martins in Sherman, Texas. Resident male martins controlled about 75% of all available rooms in a martin colony, with House Sparrows and Starlings using the remaining rooms. It is suggested that territoriality in Purple Martins has evolved to facilitate polygyny. Polygyny remains at a low incidence because competition among evenly matched males in the population overrides strong sexual selection for polygyny. This hypothesis applies to martins that nested in woodpecker holes before man provided birdhouses and to martins presently nesting in martin houses. Polygyny, as a function of territory, is further supported by the temporal contraction of martin territory. As fewer potential mates are available in the later part of the breeding season, males may profitably restrict defense of their territories and assist their mates in feeding young. Territoriality in Purple Martins resembles the "super-territory" model, which postulates that increased territory size in the early part of the nesting season serves to exclude conspecifics from nesting, increasing the territory-holder's relative genetic contribution. But this model is weakened for Purple Martins because it is doubtful that the super-territory holders exclude any conspecifics from breeding. The maintenance of minimum territories larger than 1 room may indicate that Purple Martins have not adapted completely to the high apartment-room density of artificial birdhouses, or may be an adaptation for males' holding a roosting room.
The Wilson Bulletin © 1979 Wilson Ornithological Society