Pallid Harrier breeds in Western Europe for the first time

The first pair of Pallid Harriers to breed in Western Europe has been found in the Netherlands this summer.

The birds were discovered by Willem-Pier Vellinga, a volunteer of the Dutch Montagu’s Harrier Foundation (MHF). The pair raised four chicks in a parcel of winter barley in the northern province of Groningen, The Netherlands, and are also the first pair of Pallid Harriers known to have nested in an agricultural field.

Three years ago, a male Pallid Harrier attempted to display to a female Montagu’s Harrier near Finsterwolde in the province of Groningen, the Netherlands, but was unsuccessful. Male Pallid Harriers can hybridise with female Montagu’s or Hen Harriers. According to Finnish raptor expert Dick Forsman, this interbreeding can even produce fertile male offspring. "Whether this could also result in fertile female hybrids remains unclear," he said.

This time, however, two Pallid Harriers managed to find each other and mate. MHF staff members were able to determine that both of this year's harriers were hatched in 2015 and are in their third calendar year, according to plumage details and eye colour.

When Vellinga accidentally discovered the male Pallid Harrier during breeding bird counts in May, it struck him immediately that the bird was showing breeding behaviour. Together with harrier expert Ben Koks, the breeding location was detected the following day in a parcel of winter barley. Subsequently, the nest was protected with a fence by members of the Dutch Montagu’s Harrier Foundation, to prevent predation. During the whole of their breeding cycle, the birds were studied in detail to gain insight into the ecology of this spectacular raptor species.

The female Pallid Harrier perches at the edge of its hosen wheatfield nest site (Rein Hofman/www.birdfocus.nl)

The first egg was estimated to be have been laid between 8 and 10 May, with the nest protection fence was being erected on 17 June. At that moment, five chicks of between three and 11 days old were seen in the nest. Without nest protection the chance of predation by Beech Marten or Fox was high. It was also important to preserve the nest from the elements, as heavy rains and strong winds tend to tilt the barley over and could bury the nest and chicks, ending the breeding attempt.

In early July, the winter barley was harvested, but MHF staff and volunteers were on site to prevent the young from being killed by the combine harvester. Two of the young had already fledged, while the other two could almost fly; however, the fifth chick disappeared early on. All the four remaining young were females, and were tagged with black colour rings with white inscription, just before they were able to fly.

The male Pallid Harrier passes over the female as it sits on the nest in the wheatfield (Rein Hofman/www.birdfocus.nl)

Never before has a new breeding bird species in the Netherlands been documented in so much detail as these. It also surprising that such rare birds escaped the radar of the birding community, which allowed the birds to raise their chicks in the solitude they needed, said the MHF. As in Britain, Pallid Harrier is a rarity in the Netherlands, though numbers have increased recently and several individuals have overwintered in the last two years. Still, it remains a mystery where these two birds came from and why they chose to nest in Groningen.