OF MOORHENS AND MAGPIE ROBINS
Moorhens, or poul do in Kreol, are funny looking birds that are well known in Seychelles. With conservation succeeding on several islands, the moorhen population has been exploding. On Cousin Island Special Reserve, Nature Seychelles noticed a decline in the Seychelles Magpie-Robin population, from 47 birds in December 2005 to 27 birds at the moment, in sharp contrast with the increasing moorhens’ population. Moorhens are medium-sized, ground-dwelling birds, which are usually found near water. They are not endemic to Seychelles but are considered native and can be found in all over the world. Nature Seychelles is now closely monitoring the population of moorhens and to see whether they are a threat to endemic species of Cousin Island. Eric Blais the Conservation Officer on Cousin is being assisted by students from the UK to undertake this work.
Nature is rife with competition. In common and widespread populations it is considered part of what Charles Darwin called “nature red in tooth and claw”, but in a greatly diminished endemic species such as the Seychelles Magpie robin, it can be catastrophic.
The moorhens diet overlaps with that of the magpie robin, both feed largely on ground-based invertebrates, putting them
indirect competition. Already, there have been observations of moorhens chasing magpie robins off areas where prey is abundant.
Seychelles Magpie robin Moorhen © Dao Nguyen
“Evidence suggests moorhens are competing with the Seychelles Magpie robin for invertebrate prey. Competition by another widespread and common bird that forces magpies to settle for territories of poorer quality should be regarded as a potential serious threat”, says Eric Blais.
The threat is magnified by the fact that the magpie robin has a low reproductive rate typical of endemic island birds but unlike mainland birds as the moorhen. “Nesting success is strongly influenced by the quality of the bird’s territory and the availability of food, mainly cockroaches, insect larvae, and small skinks in the case of the magpie. Therefore anything that forces magpies to settle for territories of poorer quality could delay the recovery of the species” David Derand, Nature Seychelles Science Coordinator, says. He also points out that other potential causes could also explain the recent magpie population decrease, notably a high inbreeding level, a higher eggs and chicks predation in artificial nest boxes due to geckos attraction, and for sure the negative effect of subordinates magpies that have been shown to increase the frequency takeover of established breeders, thus delaying offspring production.
The International Union for Conservation of Nature (IUCN) classifies the Seychelles Magpie robin as Endangered. Extensive conservation management has resulted in its recovery, with total population of approximately 200 individuals, 27 of which inhabit Cousin Island. The highly successful Magpie robin Recovery Program led by BirdLife International then managed by Nature Seychelles took this very rare species away from the brink of extinction when it was considered Critically Endangered to a lower level of threat which is classified as Endangered. However it still exists on only five of the Seychelles Islands with Denis island being the recent addition.
The monitoring on Cousin island will also look at the effect the moorhens population growth is having on the endemic Wrights and Seychelles skinks. These species are found in their highest densities on Cousin Island and any decline in their population would be globally significant.
There is an indication that while the moorhens’ population has increased dramatically, that of the skinks has decreased. "This may indicate that moorhens are either directly or indirectly detrimental to the island’s skink population" says Jennifer Love, the student assisting with the program.