GROWTH OF LATE-HATCHED, COMPETITIVELY DISADVANTAGED NESTLING HOUSE WRENS RELATIVE TO THEIR OLDER, LARGER NESTMATES

Abstract

Abstract We compared the growth of late-hatched, competitively disadvantaged nestlings to that of their first-hatched, larger nestmates in 12 asynchronously hatching broods in a Wyoming population of House Wrens (Troglodytes aedon). Upon hatching, late-hatched nestlings weighed, on average, 48% as much as their heaviest nestmate (range 38–60%). Late-hatched nestlings gained significantly less mass per day (0.23 g, on average) than first-hatched nestmates between the ages of 3 and 7 days when mass gain is most rapid. Late-hatched nestlings also showed a strong tendency to grow tarsi more slowly than first-hatched nestmates over the same time period (mean difference: 0.16 mm/d). Primary feathers of late-hatched nestlings, however, grew slightly but not significantly more slowly those of first-hatched nestmates (mean difference: 0.05 mm/d). Reduced rates of mass gain and tarsus growth but normal rates of feather growth have been observed in competitively disadvantaged nestlings in several other passerine spe...