Almost 1500 Nest Record Cards for the Little Grebe collected by the British Trust
for Ornithology (BTO), between 1938 and 1988, were analysed in order to understand
better its breeding biology. The numbers of cards per year decreased
following severe winters, suggesting the species' susceptibility to hard weather.
The date of laying of the first egg extended from February to September, with a
mode in early May. Modal clutch size was 4 (range 1-8), and modal brood size
3, but there were problems in observing broods reliably due to the species' secretive
behaviour. Fifty-three per cent of nests whose outcome was known were
successful; 35% of nest failures were due to flooding. Nests on ponds and lakes
were significantly more successful than those on rivers and streams; laying dates
varied significantly between wetland types, with nests on canals earliest and
those on rivers latest. Nests on rivers, subject to fluctuating water levels, experienced
significantly higher rates of failure through flooding than those on waters
such as canals, where water levels were artificially controlled.