Ever heard of moult strategies? At Mida Creek each year thousands of migrant waders drop their feathers and grow new ones ready to take them up to 8,000 km to their breeding grounds – and back. Now studied in great detail by A Rocha Kenya’s director in his recently completed PhD.
Mida Creek, a large tidal inlet tucked immediately inland from Watamu, is an internationally important site for migrant waders or shorebirds. Since A Rocha Kenya started operating in Watamu we have been spending whole nights on the creek netting waders to ring them in order to find out more about their migration routes and biology.
Colin Jackson’s PhD thesis
For his recently completed PhD, Colin Jackson, took ringing data from several thousand Greater and Lesser Sand Plovers and Terek Sandpipers – species for which next to nothing was known about their migration routes and moult strategies for the East African populations – and compared them with ringing data of populations of the same species from India and Australia.
Moult in birds is the action of replacing old, worn feathers with fresh, new ones and must take place every year if the bird is to survive. This is particularly important for the large flight feathers which, if badly worn reduce efficiency of flight and, if not replaced, could ultimately lead to the death of the bird through exhaustion or being unable to evade a predator.
Being the largest and most critical feathers, birds will put particular effort into ensuring sufficient time is available to moult them and that it is done in a place where disturbance is minimal but food is plentiful to supply the required protein for feather growth.
Mida Creek is one of those places and each year thousands of migrant waders drop their feathers and grow new ones ready to take them up to 8,000 km to their breeding grounds — and back. Hence the added importance in protecting Mida from undue disturbance by people (tourists, fishermen) or destruction of the sand flats where they feed.
Kenya, India, Australia
Comparing Kenyan birds with those in Australia and India proved fascinating – to discover how the same species will change its moult strategy depending on how far the birds need to fly from breeding to non-breeding grounds, the local climatic conditions and time they thus have available to moult.
Greater Sand Plovers in India undergo a relatively rapid moult of just 80 days pushing to complete before the intensely heavy monsoon rains and floods arrive that reduce the availability of the more surface-dwelling prey they feed on. As the monsoon hits, having completed moult they appear to leave, though where to we are yet to discover.
In south-eastern Australia, Terek Sandpipers have flown c. 12,500 km from their breeding grounds and therefore have to delay their moult much later than those in India or Kenya — on average four and half months after those in India.
Timing of moult differ
The overarching picture of moult in adult migrant waders is that those that moult far north at high latitudes, it starts early and is kept short. With decreasing latitude, the timing of moult is delayed with increasing distance from breeding grounds (all migrant waders in Africa breed in the northern temperate zone of Europe and Asia).
In the tropics the lack of constraints of approaching harsh winter weather and long distances from breeding grounds allow species to adapt a wide range of moult strategies. As birds migrate farther south, e.g. southern Australia, before they moult, constraints on time available to moult due to large distances travelled mean duration is reduced in order to fit it in.
Unknown routes unravelled
Seeking to unravel migration routes was another aim of Colin’s studies. A very direct result of this was the photographing of one of ‘our’ Greater Sand Plovers, leg flag no. ‘TA’, on a beach near Mandvi, Gujerat in north-western India in April 2015. This was the first of this species from East Africa to be recovered anywhere and suggested it’s migration route back to the breeding grounds in China or Mongolia passed through Mandvi. This was confirmed when the same ‘TA’ Greater Sand Plover was photographed on the same beach on 29 March 2016… and again on 30 March 2017!
Using formulae developed to estimate possible flying distance of a wader given the amount of migratory fat it has put on (i.e. its body weight), we could work out that it couldn’t have flown straight to Mandvi from Mida Creek, but probably flew first to Bar al Hikman in Oman, a known major feeding stage for waders, and then east to Mandvi before flying north across the Himalayas to China.
We also had a Lesser Sand Plover, flag no. S6, photographed on the same beach in 2016 and 2017 but a month after the Greater confirming part of its migration route as well.