I must admit that until recently, ‘exotic’ wildfowl did very little for me. However, an encounter in July 2014 changed my perspective, and encouraged me to look a little deeper into the assumptions that I make when encountering ‘escaped’ wildfowl.

 

It happened on July 2nd, when, on my daily lunchtime wonder around Girdle ness, a large shape sped head on towards me through Aberdeen harbour. It was a goose, and the pale grey upperwings that were evident without binoculars made me think of a greylag (itself, quite a notable bird on my patch). When I got the binoculars up I was astonished that this greylag had transformed itself into a bar-headed goose. I was immediately conflicted by enjoying the huge surprise and really striking looks of the bird, and by the knowledge that it was ‘plastic’, and in birding terms, of little value. The assumptions had kicked in already; it must have been an escape. Nothing to see here, move on....

 

And of course, technically, it was an ‘escape’. However, having posted a picture of the bird on twitter, some interesting information started coming my way. Someone alerted me to the presence of a flock of eight birds in Fife just the week before, and indeed later discussions online revealed that on the day that my bird whizzed past me, seven had been seen at the Montrose Basin. So it seems very likely that my bird could have been present in Fife a week before, but what
 were eight Bar-headed geese doing in Fife, in June?

 

A quick glance at the BTO’s excellent Breeding Atlas showed that records of Bar-headed geese in Scotland were pretty sparse during the recording period, which certainly backed up my own assumptions, never having knowingly seen one here. From here I turned to Birdguides, and Nick Littlewood kindly provided all records of the species from North East Scotland. On looking into both of these datasets, a surprising but obvious trend became clear. The North East Scotland data revealed a clear peak  of records in the late spring (May and June), with a secondary peak in autumn. The Birdguides data also revealed this spring peak although with many more records in June than in May, but no autumn peak. The records from May, June and July comprise almost half of the Birdguides dataset, and note the prevalence of June records within the Scottish subset of the Birdguides dataset, with six out of eight records from that month. The figures below show number of records, rather than the total number of individuals recorded per month. 

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I’ve had a few thoughts on the use of Birdguides data for this sort of rough and ready assessment. The unstandardised nature of birding, and perhaps more important, the reporting of what’s been seen, means that these data would be of limited use scientifically. However, I believe that in this case, the unstandardised nature of the data is what helps to emphasise the patterns in occurrence of birds outside of their usual range. No-one who encounters feral bar-headed geese every day is going to report them to Birdguides, but someone who encounters a one off, out of range bird might be more likely to do that, so I’m reasonably happy that the ‘noise’ created by sedentary feral birds will have been removed to some extent from this dataset, and that the patterns presented are credible.

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This pattern of late spring occurrence of Bar-headed geese is further emphasised by patterns from the Northern Isles. Of five records from North Ronaldsay, all are from May or June, and six out of eight records from Shetland are from May or June (with the other two records coming from April).

 

When the numbers of birds involved in records from both datasets are considered, the prevalence of June records is highlighted again. Of 10 records of flocks of bar-headed geese reported (a flock here meaning three birds or more), seven are from June. Another is from July, and the two that were not from June or July were both from Buckinghamshire, and therefore could conceivably relate to resident UK birds. 

 

So, it seems that in North East Scotland, and beyond, there is potential for a small scale, late spring/early summer arrival of bar-
headed geese, involving individuals but also  sometimes small flocks of birds. It’s only natural then to wonder where these birds have come from.

 

The bar-headed goose is a rare non-native breeding bird in the UK, first recorded breeding in 1989 and with roughly one pair breeding per year, having declined from the late 1990’s where up to nine pairs bred. Despite breeding annually it is yet to establish a regular and self sustaining breeding population. Up to 85 individuals have been recorded per year, with, for example, 65 individuals reported to WeBS during the 2013/14 recording period. Generally birds are reported as lone individuals, with 78% of the records contributed to the latest atlas pertaining to individual birds. The largest individual WeBS counts from 2013/14 were of 5 birds.

 

It is much more numerous as a breeding species in continental Europe with up to 193 breeding pairs, especially around the Low Countries. The stronghold is the Netherlands, with a population of approximately 100 pairs/350 individuals. In Belgium, there are 35 pairs/80 individuals, and in Germany, a maximum of 18 pairs. In the Netherlands, the species breeds semi-colonially. It seems more likely to me that the larger groups of birds that arrive in North East Scotland have aggregated at these Dutch breeding colonies, rather than originating in the UK, where the majority of birds lead more solitary existences. Records from migration watchpoints in the Netherlands suggest that the peak period for observing movements of this species tie in with the May and June peaks in North East Scotland. The timing also corresponds with the period that non-breeding birds, or early failed breeders within their native breeding range would make flights from breeding colonies towards moulting sites.
 

Of course, this doesn’t prove anything, and we’re left with some intriguing patterns of occurrence rather than anything more concrete. If there is any point to any of this, it is to highlight our general lack of knowledge about the status and behaviour of invasive species across Europe. This lack of knowledge potentially has impacts on UK birders, insomuch as at the least, developing our knowledge could lead to changes in the British List (proof that Bar-headed geese were arriving from self sustaining European populations would see that species move from Category E of the British list to the currently unoccupied Category C5). There are conservation concerns as well though. Invasive species are capable of posing many threats to native birds, with bar-headed geese specifically listed as being a threat on the basis of their potential to hybridise with other species of geese. Numbers of breeding bar-headed geese in continental Europe increased rather rapidly between 2000 - 2010, and there is no reason to assume that a similar increase could not happen here. It seems prudent to be aware of these issues, and as birders with an interest in conservation, contribute what we can towards increasing our knowledge of invasive species. We can do this in the same way that we contribute our data on native species - either by submitting records to county recorders, or to BirdTrack, both of which are set up to collate data on invasive species. Who knows what future value these data could have? If nothing else, they might potentially shed some light on unknown movements of birds on a European scale.

 

There’s nothing to stop us enjoying looking at them, too!