Territoriale en broedende Visarenden Pandion haliaetus in Nederland in 2020 en 2021

Territorial behaviour of Ospreys has been observed in the Biesbosch, in the southwestern Netherlands, since 2014. First breeding was proved in 2016, the pair using a nest built in a dead tree. Since then, the number of breeding pairs gradually increased to four in 2021 (plus two territorial pairs, one of which in a Scots pine on the northern Veluwe in the central Netherlands), all of them confined to the Biesbosch. Monitoring is largely restricted to observations from the ground, as nests are difficult or impossible to access. Three pairs in 2020 each raised three chicks in nature reserve De Biesbosch, and three out of four pairs that commenced laying raised 2x 3 and 1x 2 chicks in 2021. Territorial pairs with nests that apparently refrained from laying were present in the Biesbosch, near the Philipsdam (Zeeland) and on the Veluwe. Based on rings most Ospreys originated from eastern Germany, except for a male that was raised in Rutland Water (UK). In 2016-2021 the average breeding success was 2.2 young per active nest and 2.4 young per successful nest. A total of 29 young Ospreys fledged in 2016-2021. The population is growing steadily, but is vulnerable due to losses of natural nests by storms and collapsing trees and to human disturbance from increasing recreational activities in nature reserves.