Sunday, 20 June 2010

Aalamootie update

The stormies (aalamooties) have started laying! The first incubating bird was confirmed in a study nest site this week! Quite possibly there are others in study sites that have laid eggs, but it’s not always easy to see an egg beneath a bird. They are quite sensitive to disturbance during incubation, so visual inspections of nests are done infrequently and, once an egg is confirmed, a nest will not be disturbed again until close to the expected hatching date.

This news comes as a relief after the previous week, during which a number of fresh, dead eggs had been found. The eggs are incredibly fragile and can easily be damaged by the birds themselves or by the coarse substrate which the birds so often lay their eggs on – on shell sand in the boulder beach or stony ground in the stone walls.

A dead egg found just outside of a nest site, probably kicked out by a bird within.
You can see it is very fresh, since there is still yolk inside. (Hannah Watson)  

Like all petrel eggs, those of a storm-petrel are pure white, with no markings. As you can see, they are very small - less than 3cm - though, pretty big compared to the size of the actual bird. In fact, the storm-petrel lays the biggest egg relative to its body size of all birds! Given this, it will not be surprising that a female storm-petrel lays just one egg, which reflects a huge energetic investment.

An abandoned egg found in a nest site on the boulder beach - a small crack is visible
on the far left, so the egg will no longer be viable. (Hannah Watson