Tuesday, 10 January 2012

Red sauce, Brown sauce, Bean Geese

Top - Taiga Beans and others.  Middle - Wigeon making the habitat unsuitable for Taiga's. Bottom - Pinks (at least they were close).

Northern people are supposed to prefer brown sauce while southerners go for the red stuff. Not for the first time, I pondered this piece of mythology the other day whilst waiting for the Taiga Bean Geese to become rather more than distant dots on the far side of Buckenham Marshes and for their little mate, the Lesser White-fronted Goose to appear. What prompted this deep, re-sauceful thinking you may ask? Well the Taiga’s are feeding predominantly on Buckenham rather than Cantley this winter.

Only two locations regularly support populations of wintering Taiga Bean Geese in the UK: Buckenham and Cantley Marshes in the Yare Valley, Norfolk, and the Slamannen Plateau in Scotland. Ringing results have suggested that the two populations breed in different parts of Scandinavia. The majority of the individuals visiting central Scotland probably belong to a fully wild sub-population, which is distinct from the one wintering in Norfolk. Part of the central Scotland flock may also derive from a re-introduction project, which started in 1974 in central Sweden. The Scottish birds tend to arrive in October. By contrast, the Norfolk birds appear to leave their breeding area in Sweden for a wintering/staging area in Denmark, before a proportion move on to the Yare Valley around the end of the year.

Now to the brown sauce, red sauce conundrum. Taiga Bean Geese have been using Buckenham and Cantley Marshes since the 1930s with numbers peaking at 1,000 birds in the 1936-37 winter. Research has indicated that the Yare Valley Taiga’s prefer to graze on unimproved pasture, feeding particularly on meadow-grasses (Poa spp). It is suggested that the large body size of the Taiga (and their disproportionately large guts) allows a more effective digestion of taller, poorer quality food than their smaller-bodied competitors. A shift from preferring Buckenham to Cantley during the 1970s was associated with a shorter sward on Buckenham resulting from increased grazing by Wigeon and sheep. As a result a proportion of the fields at Cantley are maintained to this day at a longer autumn sward height especially for the Taiga’s. By contrast, research on the Slamannen birds has shown that they feed on ‘improved’ grass fields and particularly on Rye Grass (which is apparently less digestible for the Yare Taiga’s). So how comes two populations of birds of the same species, breeding in the same country, can be so different in their digestive traits?

Hmmm confusing. Now, there is a clue to all this in the name – ‘bean’. So called, because on the continent they traditionally feed on arable farmland in the autumn, firstly on stubbles, then on waste root crops, with a shift to cereals and grasses late in the winter. Perhaps at the end of the day the research should be seen as just a ‘snapshot’ of what is happening. Grass-feeding waterfowl will specialise on the most energetically efficient area of food determined by their body characteristics. And a number of factors will also affect where the birds choose to feed, not least disturbance, to which Taiga’s are apparently sensitive. The Bean Geese will choose to feed on what is most nutritious and available in their traditional wintering areas given the conditions that prevail. But quite clearly you can’t have brown sauce on a burger ....and red sauce on bacon is a complete no-no wherever you come from. Arrh, there’s the Lesser White-front.

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