Monday, 17 May 2010

13th May. Old Hall

With 54 pairs sitting on eggs at Old Hall Marshes it might look as if this is going to be a good year for Avocets. But how many will make it through to fledging? If recent years are anything to go by, then very few. When Avocets first colonise a site they typically are very productive but as the years go by, fledging success falls away even if the number of breeding pairs continues to increase. This has been the case at Old Hall, and at many other well known Avocet sites. Some studies show food availability as the key factor, and we know that at Old Hall last year, the average biomass of Avocet food items in the pools was only a small fraction of the recommended level. So this might be the reason. However, we also know that predation is another major factor. Avocet chicks are gobbled up by a variety of predators, not least gulls and foxes.

Whilst both these factors are probably playing a part, the broader issue is that Avocets are an ‘early successional’ species, turning up and doing well at new sites before the habitat matures and brings in other species, such as gulls, or the site productivity (in terms of food availability) drops, or the predators get to know where their dinner is likely to be located. Maintaining Avocets on a small ‘stable’ nature reserve can be difficult, and involve much scratching of heads.

Whilst in such a bout of head scratching at Old Hall, we enjoyed 3 Spoonbills, 35 Whimbrel, 2 Greenshanks, 2 hunting Barn Owls (one catching a vole), 6 or more Marsh Harriers, 2 newly fledged broods of Bearded Tits, and watched the first hatching Avocet chicks. How many will survive this year?

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