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Shore birds: making the most of living in a crowd


 
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Field Ornithologist Ricki Coughlan reveals more of the amazing lives of migratory shore birds.
Migratory shore birds gather in their many thousands on mudflats, sand bars and river banks. Somehow, they are able to live cooperatively and peacefully in close proximity to birds of their own and many other species.
This has many advantages for individual birds.
There’s the dilution effect: Just like with schools of fishes, large crowds of animals means greater safety for the individual – your chance of being taken by a predator is far less than if you are alone.

Vigilance is also important: with so many eyes and ears around to keep watch, there is more time to safely snooze or to forage head down in the water or mud.

When large flocks are disturbed from a roost by a predator, their swooping, wheeling flight serves to bewilder and foil the predator.

So, gathering in large groups is good for the individual provided they can manage to live together and not compete for food resources. Migratory waders have solved this by evolving many different culinary preferences.
For example, the single model for a sandpiper has evolved into perhaps 50 species, all with different sized and shaped bills that are all designed to seek out food as they probe about in mud or under sand. Each bill shape does this in a different way and sets different culinary choices for the different species. This means the birds are not competing with each other for food resources and so can benefit from being near many other birds harmoniously.


 
Photo below by Ricki Coughlan shows a range of migratory shore birds on the telltale red sands of Roebuck Bay.  The birds appear to be lined up to show off the different shapes and sizes of their bills

 

 
One of the outstanding features of Roebuck Bay in WA is that it is a premier location to be able to observe perhaps 40 species of migratory shorebirds together with other local species all together in great numbers. The different species feeding and living together in this noncompetitive way reflects ‘interspecies or interspecific resource partitioning. Some shore birds go even a step further so that within the same species the males and the females forage in separate areas or in a different way (called intraspecies or specific resource partitioning).
Usually the female has a slightly longer bill. This may reflect different dietary needs or to ensure the sexes are not competing with each other.

Stocking up on food resources is crucial for migratory shore birds who must make the long flights between the Arctic and Australia and back each year. To do this they rebuild their muscular and cardiovascular systems, to become ‘super athletes’. Ricki compares it to changing from a tiny Suzuki Swift to a V12 Jag motor and their blood going from standard to super.

Efficiency is maximised during the long migratory flights
, so that as their weight diminishes with their fat reserves burning up and they no longer need larger, heavier muscles and heart, their physiology gradually reverts to the smaller standard model.
These changes occur twice in the long haul back to the Arctic, once here in the southern wintering grounds and again at the refueling stopover grounds around the Yellow Sea. For many species the females even prepack their calcium reserves, increasing their bone mass by 30 percent so that they have the necessary resources to form egg shells.
In spite of these enormous physiological demands and changes and the long flights each year, migratory shore birds commonly live for 21 or even 25 years. Migratory shore birds are indeed near magical creatures - descendents of dinosaurs, and global travellers from before prehistory who throughout their lives seek to follow an endless summer.

Summary text by Victor Barry

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