miércoles, 28 de julio de 2010

Harsh reality

The image above shows one of the irrigation basins in Las Martelas, a fairly nondescript, semi-urban area on the outskirts of Los Llanos.

A pair of Moorhens (Gallinula chloropus) have established themselves in this particular pond and have already had three broods this year, consisting of 6, 5 and 3 chicks respectively. Given the relatively good habitat, compared to certain other locations where the species attempts to breed, it has always baffled me that none of the offspring so far observed have ever survived.

The two domestic ducks in the next photo also inhabit this artificial pond on a more or less permanent basis. I assume they are Mallard x Muscovy hybrids (Anas platyrhynchos x Cairina moschata). Surprisingly, both birds can fly well, despite their large size, and they move around neighbouring basins freely.
On July 25th, partly concealed among the bushes, I was busy taking pictures of an adult Moorhen as it carefully passed tasty morsels to one of its three chicks.
It was a scene I had witnessed many times before, in which each of the progenitors takes charge of feeding one or more of the hatchlings. However, despite appropriate parental care, only one, or at most two chicks tend to survive per brood of 5-6, if any at all.

As outlined in two 2009 posts, among the possible causes for this relatively low survival-rate could be the drastically varying water-levels dictated by irrigation requirements - which destroy nests and render cover untenable - together with predation by rats, cats, herons and even kestrels, or perhaps simply the limited food resources in the basins themselves.

Whatever the case, during this particular photography session, another explanation for the hatchlings' high mortality was unveiled, and I was totally unprepared for the ensuing events...

Despite the rather blurred images - my ISO and shutter speeds were set for the placid, previous scene - the violence of this sudden attack by the smaller of the two domestic ducks, and the Moorhen's desperate attempt to rescue its helpless chick, can be fully appreciated.

A few minutes later, as if nothing had happened, the adult Moorhen resumed its parental duties. The remaining chick seemed to sense imminent danger, for as soon as the parent momentarily averted its head, the hybrid duck rushed in and grabbed itself another meal...

This gruesome sequence depicts an unexpected behavioural trait of what are, in most people's minds, docile water fowl, and it came as a sharp reminder of the often harsh reality of nature.

It can only be hoped that numbers of this particular duck variety never increase to the point where they pose a serious threat to the island's small nesting Moorhen population.

domingo, 25 de julio de 2010

Squacco Heron (Ardeola ralloides) - Late July 2010

This is my second encounter with the Squacco Heron (Ardeola ralloides) on La Palma. From May to August 2009, one - occasionally two - birds were regularly seen at the same irrigation basins in Tazacorte where the present bird was photographed.

The species is described as a "rare and irregular passage migrant, recorded from all main islands except El Hierro", in Birds of the Atlantic Islands (Tony Clarke, Helm).

Regarding other Ardeidae on the Canaries, the Little Bittern (Ixobrychus minutus) bred on Tenerife in 1997, and possibly sparodically since then; the Night Heron (Nycticorax nycticorax) bred on Gran Canaria in 2008 and is a regular breeder on Tenerife; the Cattle Egret (Bubulcus ibis) has a nesting colony on Lanzarote, and the Little Egret (Egretta garzetta) also breeds there, as well as on Tenerife.

In the case of La Palma, only the Grey Heron (Ardea cinerea) and the Little Egret are seen all year round, although no evidence of either species breeding has come to light (Atlas de las Aves Nidificantes en el Archipiélago Canario, Ed. J. A. Lorenzo).
Above, the Squacco Heron uses its long, flexible neck and dagger-like bill to seize prey from a perch located some distance above the surface.
This particular basin is full of frogs: here the bird relishes a large tadpole.
When not foraging from overhanging branches, the heron stalks its prey in the water...