Over a million seabirds return to Shetland every summer to breed but
why are the islands so popular? Simply because they provide the basic
necessities a safe home and plenty of food.
Cool North Sea waters and the warmer Atlantic ocean currents mix around
Shetland bringing a rich supply of nutrients to the surface layers of the
sea. This, coupled with long hours of summer sunshine, produces an abundance
of tiny green plants known as phyto-plankton. These are food for tiny
animals called zooplankton which in turn are eaten by fish such as sandeels.
CHOOSING A HOME
Breeding sites need to be safe from potential predators and close to food
supplies. Different species choose different sites. Puffins, petrels and
shearwaters nest in burrows. Puffins have very sharp claws for digging but
given the chance will steal rabbit burrows. Shags, razorbills and black
guillemots favour boulder beaches while fulmars, gannets, kittiwakes and
guillemots like open ledges. At big colonies only the sheerest cliffs are
unoccupied.
Three species of
large gull breed in Shetland. All have yellow bills with a
red spot near the tip.
Lesser black-backed gulls are darker, grey on the
upper parts and have bright yellow legs. Greater black-backed gulls are
larger, have black backs and pink legs.
Many seabird species nest in dense colonies. Advantages include
safeguarding against predators, acting as a meeting place for potential
mates and accelerating and sychronising the onset of breeding through social
stimulation. There are disadvantages too though - notably the spreading of
disease and potential infighting between densely packed individuals. Notice
how gannet nests are almost geometrically spread. Each pair is just out of
reach of the dagger-like (and painful) bill of its neighbour.]
Skuas, gulls and terns nest inland. Preferences seem to vary when it comes
to home comforts. Shags go to great lengths, including thieving from
neighbours, to construct massive nests of seaweed. Guillemots, however, lay
their eggs straight onto cliff ledges.
FINDING FOOD
Most of Shetland's seabirds rely on sandeels
to feed their chicks. Gannets also exploit other shoaling fish like herring
and mackerel and join gulls, fulmars and great skuas in scavenging offal and
waste dumped from fishing boats. The tiny storm petrel patters along the
surface of the sea looking for plankton.
The Arctic skua does not fish itself but prefers to harass other seabirds
notably terns, kittiwakes and auks forcing them to disgorge their latest
meal.
This is called kleptoparasitism.
Gannets
with their large wingspan can feed up to 100 miles from the colony whereas
smaller species, like the Arctic tern and kittiwake can only forage a few
miles from home and are the first to suffer when food is in short supply.
