VARIATION DES EFFECTIFS NICHEURS DE HÉRONS POURPRÉS Ardea purpurea SUR LE LITTORAL MÉDITERRANÉEN FRANÇAIS EN RELATION AVEC LA PLUVIOMÉTRIE SUR LES QUARTIERS D’HIVERNAGE
Résumé
An increasing number of studies have demonstrated
a link between some demographic parameters
and rainfall indices for some Palearctic-
African migrant. Such relationships have been
shown for the Purple heron in several European
populations except in France, where variations in
the population size seem not to depend on
African wintering conditions. Here, we reanalyse
long term population data on the Purple heron
breeding in southern France in relation to a Sahel
rainfall index in the light of recent findings on factors
affecting breeding numbers on the breeding
grounds. After taking into account these factors in
the analysis, there was a positive relationship
between interannual population variation and the
Sahel rainfall index in September (r = 0.653, n =
15, P = 0.008) and October (r = 0.643, n = 15,
P = 0.01) over the period 1981-1998. The breeding
population increased following high automnal
rainfall in the Sahel. These findings are in agreement
with previous studies on this species and
highlight the necessity to take into account local
confounding factors when investigating such
broadscale relationships.