Shellness with Dark-bellied Brents

A slightly gloomy typical Sheppey long afternoon at the end of the day on a very high tide.

The fifty or more Brent Geese were happily vocalising just offshore, exploring backwards and forwards. There were one or two birds in every dozen that I thought were youngsters - unclear or very limited white neck collars - e.g. lines rather than triangles, and the flanks more evenly grey, rather than diagonally streaked pale and dark. Even as they lose these juvenile markings first-winter birds may still retain the juvenile pale tipped coverts on their backs, although even these gradually fade over the winter (Clausen et al, 1998). They are all such beautiful, if nearly monochrome, birds.

Turnstones explored the shelly beach, often well up from the waters edge. I was closer to these than any of the other birds, and they were really lovely!

Grey Plovers were perched here and there - for example on the groyne pillars just poking out of the waves. Later as the tide peaked (?) battlegroups of Grey Plovers skimmed past from the direction of Muswell Manor to the North, and settled close to the blockhouse. They gave me a very musical send-off when I left.

Again as the tide peaked I suddenly noticed about a hundred Curlews on the grazing marsh - before a passerby flushed them off out onto The Swale.

On the spit beyond the blockhouse, hundreds of Oystercatchers and dozens of Great Black-backed and other Gulls were roosting. Three or four Common Gulls, Larus canus, were seen floating just off the large glass-fronted house.

A Pied Wagtail searched the tideline.

The day finished off with a colourful sunset over the wide horizons of Sheppey, as I bumped over the ruts picked out by the headlights back to the tarmac.

I looked back at the older posts in this blog and thought about the variations in breeding success, juvenile plumages, and feeding habits of the Brent Geese noted there. I do love these geese! I also had a look at the scientific papers relating to the species. It was interesting to find a 2001 paper by McKay et al., recommending Clover as a suitable "Alternative Foraging Area" or "AFA" to tempt the geese away from winter wheat where they can cause a lot of damage. However, I thought Clover looked a bit like fast food, its growth can be very variable in different seasons according to the weather (it is "notoriously unpredictable), and therefore perhaps should not be entirely relied upon.

An alternative is grass regularly cut short, which is normally low in fibre and therefore rich in Nitrogen, although in trials by Rillington et al., 1995, in Southern England the geese show preference for, and benefit from longer grass if Nitrogen fertilised, a situation which should have a greater carrying capacity. However Nitrogen fertilisation does have environmental side-effects, and will be inappropriate in many situations, perhaps requiring an environmental derogation for the sake of the geese. Another point they made was that disturbance while feeding on land was potentially highly disruptive, frightening the geese off their pastures.

Hassall and Lane (2005) working in Norfolk argued that the geese are constrained both by nitrogen limitation and perceived mortality risks. For most of the season they exhibited partial feeding preferences by feeding on two or more types of food each day. They fed on salt marsh plants throughout the entire wintering season. In addition, from October until March they fed for part of each day on supplementary sites that were more profitable for nitrogen. In October they fed first on intertidal algae, the most profitable source of nitrogen. When this became depleted in late autumn, they moved inland to feed initially on winter wheat, where they were subject to control shooting, then onto pastures. By mid-March the pastures were no longer a significantly more profitable source of nitrogen. The geese then switched to feeding only on the salt marshes at a cost of a 39% decrease in their overall assimilation rates.

It was very interesting to see that ancillary evidence gathered in Rillington's paper also suggested that the geese on the land preferred fields with low hedges, unimproved, proximity of the sea, and no roads or footpaths. This does sound a bit like the fields at Reculver which the geese use. However at the moment, early in the winter and soon after their arrival, they still seem to be focusing on feeding on algae, etc, on the sea and in the inter-tidal zone.

The move to feeding on agricultural fields is thought to be an indirect result of historic population increases to previously known levels. The traditional wintering habitat is mostly shallow coasts and estuaries with extensive mudflats and intertidal areas, as Dark-bellied Brent Geese rarely occur far from the sea and feed on intertidal plants such as Zostera, Enteromorpha and a small range of littoral plants. Population growth during the 1980s resulted in more rapid seasonal depletion of natural food
sources. Thus, since the late 1970s, the geese have adapted to use coastal grasslands and the
early growth of cultivated cereal crops (van Nugteren 1994; Ebbinge et al. 1999). However how the populations prior to the 1930s and in the nineteenth century (and possibly earlier) managed without modern autumn sown cereals and winter pastures is rather a matter of guesswork.

Clausen et al.,  (1998) working in Denmark and NE England with the small Light-bellied Svalbard population, showed that in some years with apparently colder winters there were substantial losses of the first year birds - sometimes over 50% and in one year actually wiping all the youngsters out. They also suggested that other mortality factors might include hunting on migration routes or the wintering grounds, the availability of Zostera or its local alternatives on the wintering grounds, egg and down collection on the breeding grounds, predation by carnivorous mammals (e.g. Arctic Foxes and Polar Bears on Svalbard) on the breeding grounds, or even competition from other, larger, geese such as Barnacle Geese for nest sites, etc.