Dutch young hen harriers don't survive to breed

Recently I saw an interesting article on the website of Sovon, the Dutch Centre for Field Ornithology. Inspired by the excellent threads by @Jana I decided to share it here, as it may be of interest to some members that would have missed it because it's in Dutch. The article can be found here, and an English synopsis below.

The current Dutch population of Hen harriers got started around World War II. At its peak there were 140 pairs, breeding around the Wadden Sea and various peat marshes and heaths throughout the country. Currently, less than 10 pair remain, breeding on the Wadden Islands and the agricultural fields in Groningen. To understand this massive decline, the Hen harriers have been studied in detail since 2004. Unlike for example our meadow birds, the harriers don't have problems raising enough young, but it turned out those young rarely survive the breed on their own.

In 2019 and 2020, thirteen young Hen harriers were tagged to get a better understanding about their distribution, behaviour and mortality in winter. All birds stayed in western Europe in their first winter, in the Netherlands, Germany, France and the UK. They all hunted mainly on agricultural land. Of those thirteen birds, only two are still alive. For four birds the cause of death was identified: two died by predation by foxes and two died of malnutrition. This gives the impression that lack of suitable prey may be an important factor in the early death of many harriers.

In 2021, another nine Hen harriers, born on the Dutch islands of Texel and Terschelling, where tagged for research. No young survived in Groningen this year. Once independent, the young birds dispersed over the northern parts of the Netherlands and Germany, though the Texel-born individuals stayed longer on their birth island and some left to other Wadden islands. From these nine young, only three of four are still alive. Two were predated by other raptors and one likely died of malnutrition. Another banded but untagged individual was found predated.

In conclusion, to protect our population of Hen harriers, it is crucial to increase juvenile survival. Ensuring more suitable prey in key areas might be an important part of that. The tagged harriers can be followed using this link. Though the website in Dutch, I think the program is quite easy to follow for everyone.