the phenology, habitat selection, and interannual and seasonal changes in
breeding performance of the little grebe Tachybaptus
ruficollis in relation to the spatial structure of a shallow lake during
three breeding seasons (2010-2012). Nests were mostly located in shallow
waters, close to the shore (98.3 ± 37.9 cm), in vegetation dominated by Scirpus lacustris. The egg-laying period
started at the end of March and extended for four months until the end of July.
Overall, the mean clutch size was 4.7 ± 1.1 (N = 154) with a modal clutch of 5.
There was a seasonal decline in both egg volume and clutch size. The overall
nesting success was 60% and the chief causes of nest failure were predation
(52%) and adverse weather (20%). Breeding outcome was influenced by water
depth, nest size and year of breeding. Predation and nest flooding markedly
varied between years. Larger nests had a higher nesting success than smaller
ones. Likewise, nests located at greater water depth (further from the shore)
succeeded better than ones located in shallower water. As the little grebe
forages preferentially in shallow waters, these results suggest that optimal
nesting locations may be the result of a trade-off between conflicting
selection pressures such as foraging efficiency (better in shallow waters) and
nest predation risk (greater in shallow waters).
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