Friday, 23 December 2016

Spain 6: Purple Swamphen

Purple Swamphen
At first sight the unmistakeable Purple Swamphen Porphyrio porphyrio looks like a Common Moorhen as reimagined by Disney. Although not at all closely related to any domestic hen, they are indeed chicken sized, except for their feet which seem designed for a bird about four times as big.

Variations on the general Porphyrio body form can be found in tropical and subtropical wetlands worldwide. Aside from some minor variations in plumage, they are all very similar and in the past the various forms were treated as subspecies of a single globally distributed species. Today they have mostly been split into separate species, which leaves the nominate P.porphyrio (now renamed Western Swamphen) restricted to Spain, southern France and some Mediterranean islands. To the east it is replaced by the Grey-Headed Swamphen P.policephalus. In Spain we had good views of both individuals and a small group in the Ebro Delta in a restored wetland area.
Grey-Headed Swamphen
As with most rails they are birds of dense vegetation, in this case reedbeds. Their large feet support their weight as they clamber over and between the reeds. In fact, reed shoots and rhizomes form a large part of the diet, but they also eat a wide variety of other plants and also some animal prey including small birds and rodents.

Reproduction in swamphens has some unusual features. As well as the standard single pair model, they may also breed in small groups, with several breeding males, females, and non-breeding helpers (these last are probably juveniles from prior years). The nest is a platform of vegetation similar to the nest of a Coot, in which are laid a clutch of three or more eggs. The eggs hatch after around 23 days and the young leave the nest almost at once. They are fed by the parents and other group members for up to 2 weeks before starting to feed themselves. They fledge at 2 months and reach breeding age at around 3 years. They can live to over 20 years, but much less is usual.
South Island Takahe
As with many rails, swamphens are surprisingly good at long distance travel, and often appear well outside their normal range – in fact this year one reached the UK! This tendency has resulted in many remote islands being colonised, and in many cases these island forms became flightless. With the arrival of humans, and even more commensals such as rats, cats, and feral pigs amongst others, most of these flightless swamphens rapidly became extinct. Today only a single flightless species remains, the famous South Island Takahe P.hochstetteri of New Zealand.  Interestingly, the Australasian Swamphen P. melanotus, which was probably the ancestral form from which Takahe evolved colonised New Zealand a second time around the Maori arrived around a thousand years ago and has since established itself very widely and thrived in human modified environments. Probably because it is a recent colonist it has a full set of anti-predator defences and behaviours and is not vulnerable to mammalian predators in the way that New Zealand endemic birds are.
Australasian Swamphen
Although swamphens are currently classed as Least Concern by the IUCN, this is based on the prior taxonomic treated of almost all forms as subspecies. The Western Swamphen has suffered loss of habitat in the past 100 years and had declined considerably, but habitat restoration and reintroductions have been quite successful and the population is increasing and spreading.

Purple Swamphen, Ebro delta
In captivity swamphens often become tame and very used to humans and have been kept for their bright colours for thousands of years – even the Romans manged to breed them in captivity. As a result many have been moved around the world and escapes have established themselves in the wild. In Florida there is now a large and expanding population which is believed to have begun with the escape of captive birds after Hurricane Andrew in 1996. Already a small population has begun to breed in Georgia and it would be surprising if they did not eventually colonise wetlands all around the Gulf Coast.  It is likely that the US population is a mixture, although most appear to be the Grey-Headed Swamphen P.poliocephalus.

(images from wikipedia)

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