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A Comparative Study of Reproductive Adaptations in House and Tree Sparrows

José P. Veiga
The Auk
Vol. 107, No. 1 (Jan., 1990), pp. 45-59
Stable URL: http://www.jstor.org/stable/4087801
Page Count: 15
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A Comparative Study of Reproductive Adaptations in House and Tree Sparrows
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Abstract

I studied the reproductive biology of the House Sparrow (Passer domesticus) and the Eurasian Tree Sparrow (P. montanus) in a 1.3-ha plot in central Spain during 1985 and 1986. The breeding season of both species overlapped to a great extent, although egg laying began and peaked earlier in Tree Sparrows. Clutch size was slightly larger in House Sparrows, but it varied significantly only with the season in Tree Sparrows. Egg mass of House Sparrows was greater than that of Tree Sparrows (body size effects removed) and largely determined hatching size in both species. Egg mass increased with the laying sequence in Tree Sparrows, and egg-size dependent mortality was recorded only in this species. Tree Sparrows had longer incubation periods but shorter hatching interval than House Sparrows. Growth rates were higher in Tree Sparrows (though the difference was significant only for growth of primary feathers). Fledging mass (as a proportion of adult size) and nestling fat stores also were larger in Tree Sparrows. Nestling mortality rates and productivity did not differ between species, and starvation was dependent on hatching order in both. Fledged House Sparrows grew more rapidly than Tree Sparrows, and reached adult size earlier. Crops of young trapped within 4 months after fledging were fuller in House Sparrows than in Tree Sparrows. Young House Sparrows used abundant human feeding sources, whereas Tree Sparrows fed mainly on small indigenous seeds. Patterns of clutch size, egg size, and timing of breeding favor the hypothesis that interspecific differences in these traits are determined by energetic limitations, which constrain Tree Sparrows more than House Sparrows. An increase of egg mass with the laying sequence in the species that invested less in the hatchlings supports a brood-survival hypothesis. In both species, only the last hatched was subjected to differential mortality, even though the entire brood frequently starved. This does not support the brood-reduction hypothesis. The nest-failure hypothesis was also unsupported. Greater relative fledging mass and heavier fat stores in the species that suffered more adverse feeding conditions after fledging suggest that the fat accumulation is related to facing higher risks of starvation.

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