KOOIJ H VAN DER (1997) Are the breeding results of Purple Herons Ardea purpurea influenced by change of nest height?. LIMOSA 70 (4): 145-150.

Purple Heron Ardea purpurea nests in the Nieuwkoop study area were situated at an average height of 3.3 metres (N=446) in 1988-92, i.e., after arrival there of the Red Fox. However, mean nest-height was 5.1 metres (N=71) in 1993, and this remained about the same in 1994-96. The cause of this increase with more than 50% is unknown.
      The influence of nest-height on breeding success was studied in Nieuwkoop in 1992 and 1993. The Mayfield method was used to calculate nesting success. The incubation period is 26 days and laying-interval between successive eggs is two days. In order to compare our Nieuwkoop data with those from Camargue, France, and Ebro Delta, Spain, the number of nest-days in the nestling period was calculated for nests in which nestlings survived at least 16 days.
      Most Purple Herons began laying in the second part of April and the first part of May (Fig. 1). Breeding results in 1993 did not differ from those in 1992 and were good in both years. Thus, higher nests in 1993 were not a response to poor breeding results in 1992.
      Ten complete clutches (Tab. 1) were lost by, e.g., strong winds. (Together with the nest in two cases.) Six of these had a successful second clutch. There were no indications whatsoever for predation by Red Foxes.
      The survival rates of nests in the Ebro Delta and Camargue were considerably lower, viz., about 80% (Tab. 4). As to loss of eggs, differences between Nieuwkoop, Camargue and Ebro Delta are slight (Tab. 5). Loss of nestlings was remarkably higher in Camargue than in Nieuwkoop.
      The relatively good breeding results in Nieuwkoop support the conclusion (Den Held 1981, Cave 1983) that weather in Purple Heron wintering areas in Africa can determine fluctuations in the size of the species' Dutch (Nieuwkoop) breeding population

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