April 2011 -The Versatile Kestrel
You can often see a kestrel hovering at the side of the fields on Stocks Hill, as it hunts for food. Kestrels are unique among the falcons in their ability to windhover - facing the wind, moving through the air but remaining stationary to the ground; tails spread to help the air catching effect of their wings. They dip their heads down low, enabling them to spot their prey from an upright position when hovering. In strong wind kestrels’ ‘kite’, still hovering but remaining poised in the air, wings wide open and still. Once quarry is sighted, they swoop down with almost closed wings and with feet thrust forward to seize the victim before taking to the air again. Kestrels don’t always hunt from a hovering position but can also swoop down on prey from a post, telegraph pole or overhead cables.
Although their main prey is small mammals, especially field voles, they will take small birds and invertebrates. They are even capable of taking prey as large as fieldfare or dove. Kestrels have excellent sight and see well into the ultra-violet spectrum enabling them to see vole tracks through the grass, as they mark their trails with urine which reflects ultra-violet light. In this way they can often follow the trails back to the voles’ nests. Hover hunting expends a lot of energy and they need to recover this by eating the equivalent of several voles a day. If they catch a surplus they cache some for eating later, usually before dusk.
Kestrels do not build nests, but use old twig nests of other birds, such as crow. They also use holes in trees, areas under bridges, church towers and old windmills, and have even been reported nesting on the ground. 3 to 5 eggs are laid late April to May with about 2 days between each egg. Incubation takes place by the female usually after the third egg has been laid. An egg takes around 27 to 29 days incubation prior to hatching. Chicks fledge after about 4 weeks. It is the male that gathers food for his family, often leaving it near the nest, calling for the female to collect it. After the young learn to fly they still need to be fed by the parents for a further month while learning their hunting skills.
Kestrels are the most common bird of prey in the UK, with an estimated breeding population of around 36,000 pairs (ref. RSPB). They can live for up to 10 years but this is unlikely in the wild and only 20% survive 2 years. Starvation is the biggest killer, especially of juveniles during their first winter. Collisions, accidents, shooting, poisoning and disease are other causes of mortality. The kestrel is included on the Amber List of Birds of Conservation Concern due to the moderate decline of the breeding population over the last few years.
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