Ardea
Official journal of the Netherlands Ornithologists' Union

login


[close window] [previous abstract] [next abstract]

Moser M.E. (1986) Breeding strategies of Purple Herons in the Camargue, France. ARDEA 74 (1): 91-100
The breeding biology of the Purple Heron in the Camargue is described. The first birds return from Africa in mid-March and 96% of all clutches are initiated in April and May. The average clutch size was 3.48 eggs (range 2-5) and declined markedly with season. Egg size was closely related to the hatching weight of the chick and the smallest eggs in the clutch were always among the last to hatch; there was no pronounced pattern of seasonal change in egg size. There was no significant difference in the growth rate of the first two chicks to hatch in a brood, but lower ranking nestlings had lower growth rates. The youngest chicks from broods of three showed a seasonal decline in growth rate and also had lower growth rates than the third chicks in broods of four. The survival of entire nests was higher during the nestling phase than during the incubation period. The partial losses of eggs were mainly due to a failure to hatch. Many of the youngest chicks in a brood died of starvation. Reproductive output is probably limited at the chick-rearing stage in the Purple Heron. Adjustment of clutch size permits coarse tuning to parental rearing ability and to regionally and seasonally predictable changes in feeding conditions, while asynchronous hatching and sibling competition provide the fine tune mechanism to optimise brood size to the feeding conditions available. The clutch-size of Purple Herons in the Camargue is the smallest in Europe by almost one egg; this suggests that the area offers relatively poor conditions for rearing nestlings; some implications for the international conservation of the species are considered.


[close window] [previous abstract] [next abstract]