10.5061/DRYAD.T3B18
Brown, Charles R.
University of Tulsa
Brown, Mary Bomberger
University of Nebraska - Lincoln
Roche, Erin A.
University of Tulsa
Data from: Spatial and temporal unpredictability of colony size in cliff
swallows across 30 years
Dryad
dataset
2014
2014-10-08T00:00:00Z
2014-10-08T00:00:00Z
en
https://doi.org/10.1890/12-2001.1
853603 bytes
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Most colonially breeding animals occupy colonies that range in size from a
few pairs to thousands of individuals, but the causes of colony size
variation are largely unknown. Three general hypotheses are: (1) that
variation in colony size is maintained by fluctuating selection via
spatial and temporal changes in fitness associated with different colony
sizes; (2) that colony formation reflects heterogeneity in habitat, with
some sites having resources to support more individuals than others; and
(3) that individuals assess the presence or annual reproductive success of
current colony residents at each site and aggregate preferentially at
high-quality sites. These hypotheses make predictions about how consistent
colony size should be across sites and among years. We examined temporal
and spatial variability of colony size for >200 Cliff Swallow
(Petrochelidon pyrrhonota) colony sites in western Nebraska across a
30-year period. A colony's substrate type, annual population size in
the study area, and whether the nesting season was relatively warm or
cool, influenced average annual colony size. While some Cliff Swallow
colony sites hosted perennially large colonies and others perennially
small ones, between-year variability in colony size at most sites was
high. Annual colony size distributions were relatively stable over 30
years and provided no evidence for long-term directional changes in colony
size. The only ecological characteristic that was strongly associated with
Cliff Swallow colony size at a site was the type of nesting substrate,
with bridges tending to have larger colonies and being more frequently
occupied than other substrates. Some sites showed annual changes in colony
size consistent with the birds' basing their choice of colony on the
presence or success of conspecifics, but many sites did not conform to a
pattern expected if coloniality is a by-product of traditional
aggregation. Colony size in Cliff Swallows was temporally and spatially
unpredictable when viewed across the 30 years of this study. Each of the
three hypotheses to explain size variation may have applied at certain
sites, but the pattern of colony size variability leant the most support
to the hypothesis that fluctuating selection on group size maintains
colonies of widely different sizes.
COLONIES 1Original data used in analyses for this paper.