Hatching Asynchrony in the Yellow-headed Blackbird (Xanthocepha!lIs xantlhocephalus)
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Authors
Bommarito, Aaron Jonathan
Issue Date
1996
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
Hatching asynchrony of nidicolous altricial birds leads to a distinct size
hierarchy among siblings. Only 1 egg hatches per day which results in a large
difference in body size between the first and last egg hatched. Theory predicts
that if food is scarce, parents may find it advantageous to reduce the size of the
brood by one or two individuals so as to ensure the nutritional needs of the other
brood members. Typically the younger hatchlings will suffer the most from
brood reduction because they are the smallest and cannot compete for food as
well as their older and larger siblings. However, when the youngest hatchling
survives to approximately day 5 it has an increased chance of survival. During
the 1996 breeding season we studied Yellow-headed Blackbirds (Xanthocephalus
xanthocephalus) in the prairie pothole region of South Dakota to develop a better
understanding of the impact of hatching asynchrony on hatchling physiology
and growth during the nestling period. Originally 104 eggs were measured in 31
nests with average clutch sizes of 3 or 4 eggs. However, nest abandonment
caused us to delete 10 nests and 27 eggs. Of the remaining 77 eggs, 54 hatched
with only 20 individuals surviving to the point of fledging. Nestlings that
hatched later than other siblings increased in size rapidly at about day 5 posthatching
and almost reached the size of their older siblings by the time of
fledging. This rapid growth may have enhanced their ability to compete for food
and perhaps escape brood reduction. A reasonable explanation for the increased
growth of all hatchlings after day 5 may be related to the achievement of an
enlarged gape enabling them to eat an increased amount of food and convert it to
biomass for growth.
Description
iv, 24 p.
Citation
Publisher
Kalamazoo College
License
U.S. copyright laws protect this material. Commercial use or distribution of this material is not permitted without prior written permission of the copyright holder.