Optimal size of territory in the clay-colored sparrow, Spizella pallida

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Abstract
Territory size in 2 populations of clay-colored sparrows in Manitoba [Canada] averaged smaller than those in other open-country species of sparrows. This is probably because the territory was not used by adults for feeding or for gathering food for the young. Experimental removals of territorial males in mid-May revealed the existence of a surplus of nonterritorial birds, inindicating that there is some resistance to taking too small a territory. Investigation of several factors which could influence territory size indicated that nest predation was the most important factor in preventing the territory from becoming a very small size and that the upper limit to territory size was determined proximately by a number of factors including nesting cover and pressure from adjacent territory holders. Most male clay-colored sparrows appeared to preferentially defend an optimal size range of territories in which they maximized their reproductive fitness.