The population of
little egrets Egretta garzettain Spain is over 20,000 adult breeding birds,
making it one of the largest in Europe. Apart
from its population size and population trends, the parameters associated with
the dynamics (e.g., survival) of the species in Spain are virtually unknown. Our
aims were to develop models to assess (1) the colony growth rate, and (2)
apparent survival rate of a colony of little egrets breeding in northern Iberia. We used
capture-recapture data of little egrets ringed as chicks within the colony, of
normally < 30 adult breeding pairs, over a 14-year period starting in 1999.
Colony size was observed to be increasing in a linear tendency broken by
specific catastrophic events: a very strong hailstorm in 2004 and a pair of
peregrines Falco peregrinusthat
killed several adults in 2005. By 2012, the colony had still not reached the
size that it was before the decrease, so it can be concluded that sporadic
catastrophic events can have a significant effect on colony size and
subsequently population size, especially in small colonies. Annual apparent
survival (±SE) was constant and differed between age classes (first-years: 0.15
± 0.05; adults: 0.78 ± 0.06). Our survival estimate was relatively high
compared with other little egret populations, especially for adults. This
result, however, may not necessarily apply to other colonies given our small
sample size and the lack of data on other factors that also affect the dynamics
of the study population.
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