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1983. Differences in parental contribution among pair types in the polymorphic White-throated Sparrow. Can. J . Zool. 61: 1288-1292. We compared relative contributions to nestlings between male and female parents among different pair types in the White-throated Sparrow (Zonotrichia albicollis). The amount of parental contribution between the two main pair types, white-striped (WS) male x tan-striped (TS) female and TS male x WS female, did not differ. However, we found that (a) pairs consisting of TS males and WS females showed biparental care in which the partners made approximately equal investment in feeding nestlings; (b) males of WS male x TS female pair types contributed far less than the female, and far less than a TS male; (c) in WS pairs, males and females contributed about the same as did WS birds in mixed pairings; and (d) secondary TS females nested in territories of already paired WS males, and these females raised young unassisted by a male. We suggest explanations for these differences in contribution to nestlings between the sexes and between morphs, and we discuss optimal reproductive strategies for each sex and morph. KNAPTON, R. W., et J. B. FALLS. 1983. Differences in parental contribution among pair types in the polymorphic White-throated Sparrow. Can. J. Zool. 61: 1288-1292. Nous avons compare les contributions relatives des parents mile et femelle au soin des oisillons chez differents types de couples de pinsons a gorge blanche (Zonotrichia albicollis). La contribution totale des parents au soin des oisillons est la m2me chez les deux principaux types de couples, mile a rayures blanches (WS) x femelle a rayures beiges (TS) et mile TS X femelle WS. Cependant, (a) chez les couples formks d'un mile TS et d'une femelle WS, le mile et la femelle fournissent une contribution a peu pr&s Cgale de soins aux oisillons, (b) chez les couples form& d'un mile WS et d'une femelle TS, le mile contribue beaucoup moins au soin des oisillons que la femelle ou qu'un mile TS et (c), chez les couples h miles et femelles WS, le mile et la femelle fournissent au soin des petits h peu pres la meme contribution que les oiseaux WS des couples mixtes, enfin, (d) les femelles TS secondaires nichent dans les territoires de miles WS dejh accouplCs et ces femelles elevent leurs petits seules. Nous tentons ici d'expliquer ces differences, entre les sexes et entre les morphs dans la contribution des parents aux soins des oisillons, les strategies reproductrices optimales de chaque sexe et de chaque morphe font I'objet d'une discussion. [Traduit par le journal] Introduction(or) the weight at fledging of the young (e.g., lighter Differences in behaviour, ecology, and mensural young at fledging survive less well than do heavier characteristics have been found between the brightly young in the Great Tit, Purus major; Penins 1965, coloured (white-striped WS) rnorph and the dull-1979). In this paper, We report On relative contributions coloured (tan-striped TS) rnorph of the White-throated to nestlings of male and female parents ...

In this study we investigated one possible proximate factor underlying year-to-year changes in mean territory size in song sparrows. We tested the hypothesis that birds defend smaller territories if they settle more or less at the same time, than if they settle on territories asynchronously. This idea is supported by some anecdotal field evidence in birds. To carry out the test, we did two types of removal experiments: (a) removing all the territory holders in an area at the same time and (b) removing territory holders one at a time, with 3- to 4-day intervals between each removal. Both types of removal were done in October 1972, coinciding with the fall peak of territorial activity, and in March 1973, coinciding with the spring peak. All the empty territories were rapidly refilled by juveniles that had previously been non-territorial; thus the breeding density of song sparrows is limited by territorial behavior. The replacement males were bird's that had been dominant in winter flocks of juveniles. For the two simultaneous-removal areas, territory size decreased significantly after resettlement, while for the successive-removal and control areas there was no such change. This shows that settlement patterns can influence mean territory size, and may be a proximate mechanism underlying annual fluctuations in size of territories.

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