Basin Notes - October 2005

Size Matters!

The autumnal influx of migratory birds to the Basin is in full swing and the mud at low tide is filling up with many hungry beaks probing for food. When it comes to the scramble for survival and getting enough food - Size Matters.

This is not, however, a scene of wildlife in conflict with the bigger birds bullying the smaller ones out of the prime feeding sites. Nature has had millions of years to sort out the evolution of the different bird species and a hierarchy of size is one answer.

The group of birds classified as waders is the perfect example of this. These long legged birds crowd the shallow, muddy margins of bodies of water to feast on the host of small creatures that burrow in the mud for safety.

Top of the wader host is the curlew. This tall wader with the elegant gait and evocative, bubbling call can stand in the deepest water and dig the deepest with its long curved bill to get the lugworms and crabs that it relishes.

Next is the oystercatcher. Loud and brash, it tolerates no interruption from it fellows as it attacks cockles and mussels with its huge hammer-like bill.

Called the "Sentinel of the Marsh", the redshank patrols the waters edge pecking at the surface for snails and shrimps. Its nickname comes from the fact that it is the first to spot danger and makes a loud alarm call that other birds recognise and respond to with a fast take-off.

Knot search for molluscs as well and can be seen in flocks, head down, probing the mud surface as they walk.

The next in the size stakes are the eponymous turnstone, which bulldoze their way through the seaweed and stones on the margin between mud and grassy banks for insects, sand-hoppers and small snails.

Smallest of all is the dunlin that "stiches" its way along the mud at the waters edge for small invertebrates. They can easily walk under a standing redshank and often are found on the edge of flocks of knot.

There is usually about 7,000 of these waders in total on the Basin at any time in autumn and winter and yet they all find enough food to eat because they are different sizes. They have different length legs so they can stand in different depths of water and they have different length bills so they can probe to different depths. They also prefer different types of prey so they can all dine in peace and eat their fill.

This community spirit means they can help each other when danger threatens. Recent sightings of the local peregrine falcon have seen all the waders take off at once when an alarm call is heard and this mass response make it harder for the peregrine to single-out a bird to chase and reduces the odds of any one wader being caught.

So, size matters in finding a niche for all the species and bringing harmony to the Basin's wading birds.