Dispersal from the Natal Colony of the Grey Heron Ardea cinerea Nesting in Poland

Abstract. Natal dispersal is the movement from the natal site to the colony of the first reproduction, while breeding dispersal is the movement from one breeding colony to another within or between breeding seasons. These processes are major determinants of genetic structure and a key component of population dynamics. In this study we investigated whether age of recovered bird (immatures, adults) and/or period (three multi-year periods characterized by various climate change dynamics) of recovery from the breeding season affect distance and direction of dispersal from the natal colony in Grey Herons Ardea cinerea nesting in Central Europe, in Poland. We found that the distance of dispersal from the natal area for Grey Herons ranged from 0 to 392 km with mean ± SD 84.1 ± 99.1 km (N = 72). Independently of periods, individuals recovered as immatures had longer dispersal distance than those recovered as adults. Our study revealed that proportion of recoveries representing strong natal fidelity (within the distance of ≤ 38 km around the natal colony, N = 37, 51.4%) differed significantly between the studied periods with the highest proportion (71%) in 1981–2014 and lower proportions in periods 1932–1939 (35%) and 1940–1980 (27%). We also found that the distance of dispersal from the natal colony was affected significantly by the period, with the distance in 1980–2014 being significantly shorter compared to 1940–1980 and with a tendency to be shorter than in 1932–1939. Direction of dispersal from the natal colony was affected significantly neither by period nor age of recovered birds. On average Grey Herons dispersed with a marked SW directional component. Our results indicate that Central European population of Grey Herons have shortened average distance of dispersal from the natal colony since the 1930s. This observation is concordant with changes reported for other European waterbirds.