A feathery mystery

Social media is a wonderful source of information. As we drove to Bhigwan lake, one of The Family’s friends wrote to her about the stray bean goose which had been sighted there, adding that it came from Finland. Bean geese have been spotted in India four times before (most recently a solitary bird in Corbett NP in 2012, and a group near Jaipur in 2017), so it is a pretty rare sight. Neither it, nor the bar-headed geese (Anser indicus) it was with were tagged, so there is no chance that anyone can tell you definitely where it came from and exactly what it is. The staccato definiteness of social media means that it is also a wonderful source of misinformation. But then, a Puneri newspaper reported that it is definitely a Tundra bean goose (Anser serrirostris). I’ll tell you in this post that both stories are wrong. The bird is very likely to be a Taiga bean goose (Anser fabalis johanseni) from the west-Siberian taiga. I know this is a long post, but I hope you’ll read it through. I would understand though if you just look at the photos.

This is a mystery in two parts. What exactly is the grey-brown bird and what is it doing in a lake in Maharashtra? And with any mystery, you unravel it by looking for the means, the opportunity, and the motive. The big clues here are the appearance of the bird, and the fact that it seems to be associated with a group of four bar-headed geese (the local guides know this very well, and alert each other about the appearance of the bar-headed geese in any part of the lake). By examining the means and opportunity of its travel to India, I think we reach an identification. So let’s handle that first. From its gross appearance (brown and grey feathers, black bill with orange band across the middle, orange legs and feet) it could be a Tundra or a Taiga bean goose. You’ll see in a photo later that the upper wing coverts differ from those of the Tundra bean goose, making this ID unlikely. It is the same size as bar-headed geese which makes it unlikely, in a statistical sense, that it is a east-Siberian Taiga bean goose (A. f. middendorffii).

But first let’s turn to the bar-headed geese, because there is no confusion about them. There are two separately breeding populations, the western ones breed in central Asia, from Kashmir north to Kyrgyzstan and migrate south to western India in winter. The eastern population, from Mongolia and China, migrate in winter over the Himalayas, flying at a height of about 9 Kms above sea level to come to eastern India. No other bird is known to be able to fly that high. The fact that vagrant bean geese have never been sighted in eastern India is likely to mean that they cannot match bar-headed geese in their record breaking flights.

Tundra bean geese have two breeding populations. The western population can be found around the Kara sea, between Novaya Zemlya in the west and the Taimyr peninsula in the east. The eastern geese breed on the shore of the East Siberian sea. They have no well-defined wintering grounds, migrating in small groups to the balmy south in Scotland, northern Germany and Poland, or Mongolia and the Russian planes. The group that came to Jaipur was a statistical fluke. It would be even more of a fluke if a single bird got separated from its group, found bar-headed geese, and flew with them. Piling one unlikelihood over another is uncalled for, since the appearance and call of the animal already told me that it was not likely to be a typical Tundra bean goose.

The Taiga bean goose is a different beast. There are three subspecies, corresponding to three breeding populations. The Anser fabalis fabalis breeds in the north of Sweden, Norway, in Finland, and east into north-western Russia. They migrate to Germany, Denmark, Scotland and England in winter over the winter flyway. The central population, A. f. johanseni, take the central flyway in winter, south from the vast steppes of central Russia, to central Asia at the northern end of the range of bar-headed geese. The eastern subspecies, A. f. middendorffii, takes the eastern flyway from the Asian parts of Russia to winter in China, Korea, and Japan, far to the east of the breeding grounds of bar-headed geese.

Consider now the means and opportunity! Only the central population of Taiga bean goose, Anser fabalis johanseni have the opportunity to become separated from its own group and be incorporated into a flock of the western population of bar-headed geese. Since these bar-headed geese do not fly at record breaking heights, the bean goose we saw also had the means to fly with its accidental companions to a lake in Maharashtra. We confirmed that by call and appearance it resembles Anser fabalis, and eliminated Anser serrirostris not only by these classic clues that birders look for, but also by the means and opportunity to be incorporated into a flock of bar-headed geese.

How can a bird be identified?

Usually by its appearance and call. But in some cases this is complicated by an unusual similarity of two species.

Then one often relies on other clues, like where did one see it? This works if the ranges of two birds do not overlap. But if it is a vagrant, then you don’t know where its range is.

But sometimes birds are tagged by ornithologists. If a bird is tagged, then the tag will usually tell you about its history. If it is not, even then there are other tests, such as DNA matching. But these are invasive methods.

What’s the lost goose?

From its appearance it seems to be either a Taiga or a Tundra bean goose, but more likely to be the first.

Since it’s in a group with bar-headed geese, it should have come from a region where they can meet. This is only possible for the west-Siberian Taiga bean goose, Anser fabalis johanseni

And the deeper mystery? The motive? One can be even less sure, but I suspect that it was entirely by chance. A member of one migrating flock found another quite by chance on a major migration highway. Will it ever go back and find a mate? The chances are slim, but, for its sake, I hope it does. Its habits are slightly different from those of the rest of its flock. They flew and swam together, but it strode off by itself to walk on the land, and pick at food. The bar-headed geese never left the water in this time. They called just before take off, and it wheeled smartly and joined them in flight. I hope it finds a mate eventually.

But behind this individual lurk larger questions. Why are we seeing so many vagrants now? There is certainly a disruption of migration patterns, with species creeping up in altitude and latitude as the earth warms. This gives more opportunity for accidental meetings between different migrating species, producing solitary vagrants. Is it that, or does social media also alert us to events which we might not have noticed before? After all sailors in the 18th century recorded three egrets flying over the Tasman sea, but the world did not rush to view them. But I think there is an even larger question. The behaviour of the geese that I saw seemed to have purpose. They did not behave like malfunctioning automatons. The bean goose went off from the bar-headed to search for its food, but they called before taking off, and it responded to that call. The bean goose was accidentally separated from its own flock, why has it not got separated from this flock of strangers? Why do they call to it as they are leaving, and why does it respond? The answers could nuance our understanding of the separation between us and the rest of nature. In the coming climate cataclysm, who is to say that understanding such inter-species cooperation might not become a matter of human survival?