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Summary: Hormonal Correlates of Siblicide in Gala´ pagos
Nazca Boobies
Elisa M. Tarlow,* Martin Wikelski,*,
,1
and David J. Anderson
*Department of Ecology, Ethology and Evolution, 505 S. Goodwin Avenue, University
of Illinois at Urbana-Champaign, Urbana, Illinois 61820; Department of Ecology
and Evolutionary Biology, 303 Guyot Hall, Princeton University, Princeton,
New Jersey 08544-1003; and Department of Biology, Wake Forest University,
Winston-Salem, North Carolina 27109-7325
Received May 16, 2000; revised November 20, 2000; accepted February 28, 2001
Nazca boobies (Sula granti) show unconditional obligate
siblicide immediately after hatching, reducing the typical
two-egg clutch size to one. We studied body mass
changes and levels of testosterone (T), corticosterone
(CORT), and progesterone (P) for A-chicks (dominant,
first hatched), B-chicks (subordinate, second hatched),
and singletons, during the first 7 days after hatching,
when siblicide normally occurs. Mass increase with age
was higher for A-chicks than for singletons and
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