Breeding Colony Fidelity and Long-term Reproductive History of Individually Marked Wild Grey Herons

Abstract

Abstract. Site fidelity to the colony and breeding histories of individual Grey Herons Ardea cinerea were examined by intensive and long-term (nine years) observations of 50 fledglings and 19 adult birds banded with colour-patterned rings in a single-species colony in suburban Tokyo. In total, 38 (76.0 ) of 50 marked fledglings were never resighted in the natal colony. Of the 12 returning birds, four (33.3 ) began to breed at 2-years-old, two (16.7 ) at 3-years-old, one (8.3 ) at 4-years-old, and five (41.7 ) never bred. Two birds survived after 9 years from fledging. In total, 18 (94.7 ) of 19 adult birds were resighted in the next breeding season and most of them (15/18) bred there. Birds tend to stay at the same breeding colony once they had returned. Some birds exhibited site fidelity to the breeding nest every year, but others did not. Pair bonds remained stable in four pairs throughout years until one individual in a pair was lost. The number of chicks fledged per nest did not change with the age of the parent. Two broods in the same breeding season were observed in 7 (9.0 ) of 78 nests, in which at least one parent was marked. The maximum number of fledglings produced by a single male over the 9 years was 22. Of 23 birds that were resident for more than two years, four birds (all females) continued to stay at the colony site after the breeding season. However, 19 birds (eight males, three females, eight unsexed) left the colony after the late breeding season and were observed in outside locations, particularly at fixed feeding sites. The maximum distance of resighted, marked fledglings was 1,580 km southwest of the colony, 54 days after release.