Saturday, 10 January 2015

Brent Geese

As reported previously, one of the highlights of our birding on New Year’s Day was finding a flock of ten Dark-bellied Brent Geese in the Ria Formosa.  These are birds that breed in Siberia and normally spend the winter in Western Europe, mainly in the south of England, northern France and the Dutch/German Wadden Sea.  It was surprising therefore to find these in southern Portugal and the species is rightly considered to be a rarity here.

Dark-bellied Brent Goose, Lagoa dos Salgados, 07/01/2015

We now know that these ten geese seen near Faro are only part of the story and that there has been quite an influx of Brents into Portugal in the past few weeks.  There was a single bird in the Estuário do Cavado in the north of the country as early as 27th October and there were a few reported further south around Peniche and Lagoa de Óbidos early in December but it wasn’t until after Christmas that it became clear that something a bit unusual was going on with birds at the Ria de Aveiro, Lagoa de Óbidos, Lagoa de Albufeira and the Estuário do Sado.  In the Algarve, there have been birds in the Ria Alvor (5) and at Lagoa dos Salgados (1) as well as those in the Ria Formosa.

Because birds may be moving around it is difficult to be precise about how many of them there have been but Gonçalo Elías has collated the records and estimated the total to date to be between 62 and 82.  Although recent winters have seen small numbers of Brents arriving in Portugal, there hasn’t been an influx on this scale since 1991/92 when 110 birds were reported here, 73 of them in the Ria de Aveiro.

Dark-bellied Brent Goose, Lagoa dos Salgados, 07/01/2015

What is interesting and has been drawn to our attention by Edmund Mackrill, who has been counting and ageing Brent Geese in Lincolnshire for almost 30 years, is that the 1991/92 influx and this latest one follow particularly successful breeding seasons.  Is there a connection, we wonder?

It has been suggested that breeding success in the tundra is connected to the 4-year Lemming cycle.  This may be the result of predators such as Arctic Foxes switching to eat eggs and young birds in years when Lemming numbers are low.  If that is so, one might almost say that the occurrence of Brent Geese in Portugal is at least loosely correlated with the breeding of a small, furry rodent in the Arctic - not something that would readily spring to mind!

You can find out more about Dark-bellied Brent Geese here, here and here.  You can see here a short clip showing an adult and three young birds at the Lagoa de Albufeira, which apart from anything else demonstrates just how approachable these geese can be and this has been a feature mentioned by observers elsewhere.  It was certainly true of the bird at Lagoa dos Salgados that we saw on 7th January.

It would be very interesting during the coming days and weeks, if any birders seeing Brent Geese here in Portugal could age them and perhaps determine brood sizes and then post details in a comment here on the blog.

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