Sunday, 13 June 2010

The short Shetland summer nights

At this time of year, the stormies are just returning to their breeding colonies, having made the long journey north from their wintering grounds (or ‘waters’, perhaps being the more appropriate word!), probably somewhere far off the coast of West Africa. Due to their small size, they are highly vulnerable to predation; consequently, they only return to the colony under the cover of darkness and nest in the relative safety of the numerous cavities in the dry stone walls, boulder beaches and in the broch itself. Consequently, it is to be a nocturnal lifestyle for storm-petrel researchers.

The sun slowly descends in the sky as we patiently wait for darkness

Each evening, we eagerly wait for darkness, anxious to see and hear the stormies flooding back into the colony, either to take up occupation of an established nest site or in search of a suitable site and the perfect mate. Frustratingly though, at this time of year, at such high latitudes, darkness arrives late each night and doesn’t hang around for long. Depending on the extent of cloud cover, some nights it never seems to get that dark. You can certainly get around without the need for a torch (or ‘lamp’, as they call them here in Shetland) even when there is some cloud cover.

European storm-petrel in the hand

Some time shortly after 11.30pm, as darkness takes over, one-by-one, the birds slowly begin to appear, their silhouettes clearly visible against the dim backlight of a Shetland summer night, as they whizz back and forwards. One could be forgiven for thinking they were bats, for the speed and nature of the storm-petrel’s flight, their small size and almost totally black plumage, is not so dissimilar. Though, there are no bats in Shetland. Maxim Gorky, the Russian writer, described the flight of the ‘stormy-petrels’ like ‘a streak of black lightning’. As the darkness intensifies, the purring and chattering of the storm-petrels increases in volume, as more and more birds join in the cacophony. The purring is relentless, except for the breath note taken every couple of seconds, which sounds much like a hiccup. Song is frequently interrupted by numerous chatter calls – a rapid series of harsher notes of variable pitch. With skilful use of your ears, you can identify a pair in a nest and eavesdrop on their exchange of purring and chattering. Dan made some great recordings last week, but haven't figured out if I can upload one here yet...

Typical nesting habitat of stormies - almost impossible to find them at times!

Birds can maintain this constant song for hours on end, though, here in Shetland, are largely restricted by the short periods of darkness. Before the sky begins to get brighter again, there is a period of brief, mass exodus, as birds depart their nest sites and whizz back out to sea, reaching probably at least 150km offshore before the sun has risen. Not all birds leave the colony before light, remaining in their nest for the duration of the day. Some of those birds will produce occasional bursts of song during the day, but the majority keep quiet until darkness comes again. There appear to be significant numbers of birds that are remaining in the colony during the day, which perhaps an indication that food supply is plentiful, such that they don’t need to head back out to sea to feed every day. Fingers crossed this bodes well for a productive season...