The Tale of the Bird-Eating Tree
by NATURE SEYCHELLES
Early findings of monitoring being carried out on Cousin Island Special Reserve by Nature Seychelles’ conservation volunteers suggest that Pisonia grandis (Bwa Mapou) is having a serious impact on the seabird populations here. Impacts on White terns and White-tailed tropicbirds are of particular concern. Previous studies on Cousin have indicated that Pisonia seeds have a serious impact on the seabird populations.
The findings were presented
by Nature Seychelles’ volunteers
Gareth Davies from the
University of East Anglia and
Wayner Meyer a Conservator
from South Africa at a public
presentation on 1st July 2010, at
the Island Conservation Centre,
Praslin. The talk was part of
Nature Seychelles on -going program
to share its work with
other stakeholders and the community
on Praslin. It was attended
by the staff and volunteers
from Cousin Island and representatives
of Cousine Island, Aride Island
and environmental organizations on
Praslin including the Seychelles Island
Foundation.
Gareth and Wayne have both been leading this Nature Seychelles project on Cousin Island for the last couple of months, with Gareth monitoring the impacts of Pisonia on seabirds and Wayne looking at the possibility of vegetation diversification.
Seabird populations worldwide are in decline and therefore any factor which represents a source of mortality for seabirds represents a cause for concern. We have 7 species of seabirds on Cousin Island – the lesser noddy, brown noddy, white-tailed tropicbird, white tern, bridled tern, Audubon’s shearwater and wedgetailed shearwater.
Pisonia trees produce seeds several times a year. These seeds are very sticky and become entangled in the feathers of seabirds, preventing them from flying and finding food, and often resulting in their death. Gareth was monitoring the number of birds entangled in Pisonia in different areas around the island, to try and estimate the total number of birds which are affected. Entangled birds were cleaned, and marked to prevent recounting. He was also investigating the germination of Pisonia.
So is there anything we can do about this? While Pisonia has a negative impact on seabirds, it also provides nesting sites for seabirds and Seychelles Magpie robins while providing a source of insects for Seychelles warblers and the magpie robins.
Part of this Nature Seychelles’s long term project, implemented with Wayne’s assistance, is looking at the potential of other native tree species to fulfil this important role. Several survey areas around the island which contain a large proportion of Pisonia trees have been set up, and detailed surveys of the vegetation, seabirds and insects have been done within them, in addition to surveying the number of birds entangled in Pisonia. Wayne has also started propagating seeds of other native Seychelles tree species. The next stage of the project will involve propagating these species within the plots being monitored where Pisonia do not occur or have been removed. These species include Takamaka, Badamier and the Looking Glass Tree. The surveys will be repeated to determine whether these other tree species can also provide nesting sites and food. However, we need to wait until the seabirds, in particular the lesser noddies, which are currently using these areas for nesting have left, so the birds are not disturbed by these activities.
Source: Regar 7-9-10