Recent changes in the diet and breeding parameters of the Purple Heron Ardea purpurea in southern France

The Purple Heron population in southern France suffered a 46% decline betwe en 1981 and 1994. A study of breeding biology was instigated in 1997 in ord er to examine potential changes in the main breeding parameters between the early 1980s arid the late 1990s. Here, we present data on the breeding bio logy and diet of breeding Purple Herons in the Camargue, southern France, c ollected from 1997 to 1999. These results were compared with those from a s imilar study conducted between 1979 and 1982. No difference in first spring arrival date on breeding grounds was rioted between these two periods. Mea d first egg date was 22 April during 1979-82, in contrast to 6 May during 1 997-99. Mean colony size was c. 118 breeding pairs during 1979-82, bill onl y c. 59 during 1997-99. For broods of three arid four chicks, linear growth rates for rank A (first hatched) chicks were higher during 1979-82 than du ring 1997-99. For broods of four chicks linear growth rites were also highe r for rank B (second hatched) chicks and tended to be higher for rank C (th ird hatched) but lower for rank D (fourth hatched) chicks. During 1979-82 n estling diet (determined from regurgitates) was dominated by fish (85.4% by biomass). There was an increase in the proportion of insects from 12.8% du ring 1979-82 to 21.7% in 1998 (from regurgitates), whereas the proportion o f fish was 61.3% in 1998. Diet was determined from pellets ill 1999 and ind icated that 42.6% of the biomass was insects whereas 33.8% was fish. No dif ference was found between 1979-82 and 1997-99 for clutch size arid hatchlin g mass. Results suggest that birds needed more time to initiate breeding du ring 1979-82 than during 1997-99. Possible causes for the observed differen ces in the Purple Heron breeding biology and diet between both study period s are discussed.