Monday, 4 June 2012

A Balkan invader

At around the same time the marshes of Britain were echoing to the bellows of fighting aurochs, a bird that would be an astronomically mega tick for a birder was nesting in fens across southern Britain from the Somerset levels to what would one day be called Norfolk. Today the Dalmatian Pelican Pelecanus crispus is found no closer to the UK than the Balkans, but from the Neolithic almost to Roman times it was a regular part of the British avifauna. How and why it ceased to be a British bird is something of a mystery, but the ecological requirements of the species today offers some clues.

The Dalmatian pelican during the breeding season is usually found inland, where it nests in colonies up to 250 pairs strong on islands in lakes. The colonies have a limited life as the trampling by the huge birds destroys the vegetation, so an individual site today on average only lasts about 3 years. The clutch size is up to 4 eggs, and the chicks take up to 12 weeks to fledge. The young will take several years to reach maturity, but are long lived. The very similar Australian Pelican for example can live to 25 years old, possibly more.

The Dalmatian Pelican is the largest living pelican, and can weigh up to 15kg or more. As with most large predators, Dalmatian Pelicans eat whatever is easiest to catch – mostly carp, roach, or pike in the breeding season. In the winter, when it disperses towards the coast or migrates longer distances, it feeds on sea fish, eels, or smaller prey like shrimps. It is a social bird, and will feed collectively to herd shoals of fish together.

How soon after the end of the last Ice Age the Dalmatian Pelican arrived in Britain is unclear, but at the height of the last glaciation it would undoubtedly have been confined to the Eastern Mediterranean. As the climate warmed, it could have spread up the Danube and then down the Rhine to arrive in northwest Europe and Britain. Around 6200 BC the Atlantic climate period began. From then until 3500 BC the British climate was the warmest since the end of the last glaciation, and it was during this period that farming arrived in Britain. The first farmers had followed much the same route as the pelicans, but humans had already been long resident in Britain by then. These Mesolithic peoples had lived off wild plants, hunting, and fishing, but were not necessarily nomadic as is sometimes portrayed – fishermen tend to stick close to their harbours.

If pelicans were already nesting in Britain by the Mesolithic it is unlikely that the human population would have had a significant impact – they certainly did not prevent the initial colonisation and in any event the population was too low to be of significance. Farming allowed much greater numbers of people to inhabit the area, and they would have had much more impact on the birds, not so much by direct hunting than by fire setting in marshes to improve grazing, and disturbance of the breeding colonies by their livestock.

The loss of pelicans from Britain was probably due as much to climate change as to people. Towards the end of the Iron Age in southern Britain from around 650 BC the climate became noticeably cooler and wetter. This would have seriously impacted nesting success and was probably the cause of the pelican’s extinction as a nesting bird, although as late as Roman times it was apparently still present in northwest Europe. The Romans carried out extensive drainage of fenlands for farming in Britain and elsewhere in northern Europe, further reducing the habitat and potential sources of recolonists as the weather warmed again during Roman times.

Today, the Dalmatian pelican is classed as Vulnerable. The population centred on the Balkans has around 5,000 adults, while the central Asian population centred on Kazakhstan has around 6-9,000. Major threats are habitat disturbance, organochlorine pesticides, persecution by fishermen, and some hunting, especially in Mongolia, where the bill is supposed to have special properties in the care of horses. The Balkan population is reasonably secure, and in fact has increased slightly, but the Mongolian population is on the verge of extinction. The chances of a reintroduction project in the UK are non existent unfortunately, as the absence of the bird from western Europe suggests that conditions are no longer suitable for it. Unfortunately, pelicans as a group do not have a good breeding record in zoos, and the giant Dalmatian Pelican would probably be harder than most to breed, as it would require several pairs and a very large lake to encourage nesting, a luxury most zoos do not have. There are some in UK collections – I believe Paignton has them – but I have not found any records of them being bred.

(image from wikipedia)

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