COMPARATIVE NEST-SITE SELECTION AND BREEDING SUCCESS IN 2 SYMPATRIC ARDEIDS, BLACK-CROWNED NIGHT-HERON (NYCTICORAX-NYCTICORAX) AND LITTLE EGRET (EGRETTA-GARZETTA) IN THE ARIES DELTA, MACEDONIA, GREECE

We studied nest site selection and breeding success of Black-crowned N ight-Herons (Nycticorax nycticorax) and Little Egrets (Egretta garzett a) in the Aries Delta (Greece) from 1988 to 1990. Both species nested above the middle of tamarisks and alders. Nest density varied each yea r from 333.3 nests/ha to 646.2 nests/ha for Black-crowned Night-Herons and 291.7 nests/ha to 421.5 nests/ha for Little Egrets. Black-crowned Night-Herons started to breed earlier than Little Egrets, also placin g their nests higher (mean nest height: 4.21 +/- SD of 0.80 m and 3.54 +/- SD of 0.71 m for Black-crowned Night-Herons and Little Egrets, re spectively). The nearest neighbors were conspecifics for Black-crowned Night-Herons and heterospecifics (Black-crowned Night-Herons) for Lit tle Egrets. The mean distance of the nearest neighbor was similar in b oth species (1.02 +/- SD of 0.46 m and 1.11 +/- SD of 0.37 m for Black -crowed Night-Herons and Little Egrets, respectively). In contrast to late-nesting Little Egrets that located their nests lower, Black-crown ed Night-Herons maintained a constant nest distance from the ground. T he mean clutch size (3.40 +/- SD of 0.60 and 4.32 +/- SD of 0.81 for B lack-crowned Night-Herons and Little Egrets, respectively) and the mea n chick survival per nest (2.48 +/- SD of 0.95 and 2.53 +/- SD of 1.28 for Black-crowned Night-Herons and Little Egrets, respectively) of bo th species varied among the study years. No variation was observed in the means of clutch size and chick survival per nest of Black-crowned Night-Herons among the 3 sub-periods of the breeding season. Little Eg ret clutch size and mean number of eggs hatched was smaller in late ne sters, but no difference was observed in chick survival per nest betwe en early and late nesters. Nest placement did not affect chick surviva l in Black-crowned Night-Herons and only marginally in Little Egrets.