Abstract:
The general objective of my study was to monitor proximate causes and
seasonal patterns of hatching asynchrony and chick survival in the Ring-billed Gull
(Larus delawarensis). Two different plots were set up at a Ring-billed Gull colony
near Port Colborne, Ontario in the summer of 1992. One group was from 'peak'
nesting pairs (clutches initiated between 15 April and 1 May); a second group was
from 'late' nesting pairs (clutches initiated between 9 .. 22 May). Despite equal
intra-clutch egg laying intervals between the peak and late periods, intra-clutch
hatching intervals lengthened as the season progressed (ie. hatching became
more asynchronous). Clutches from both periods were monitored for nocturnal
attendance and brood patch development of parents was monitored during the egg
laying period. Late nesters were characterized by an absence of nocturnal
desertion, substantial brood patch defeatheration at clutch initiation and a
reduction in the number of chicks fledged per pair. Chick survival to 25 days
(taken as fledging) reflected patterns of chick mass at brood completion and five
days post-brood completion, in peak clutches. In late clutches, survival was poor
for all chicks and, was partially independent of hatching order, due in part to
stochastic events such as Herring Gull predation and adverse weather. In both the
peak and late periods, last-hatched C-chicks realized the poorest survival to
fledging among brood mates.
An artificial hatching pattern (manipulated synchrony) and an artificial
hatching order were created, in three-chick broods, through a series of egg
exchanges. In peak and late clutches manipulated to hatch synchronously (s; 24
h): C-chick survival to fledging did not differ from the survival of A- and B-chicks, in
the peak period. In the late period, the survival of C-chicks was significantly lower
than that of A-chicks. In peak clutches manipulated such that chicks from last-laid
eggs (C-chicks) hatched 24 h - 48 h ahead of the A- and B- chicks, C-chick survival
was greater than in controls. Within those broods, C-chicks survived better on
average than both A- and B- chicks.
