Most of our summer migrants have now arrived in force. Some species, the warblers and swallows, started to arrive a few weeks ago; some species, nightjars and spotted flycatchers for example, have only now turned up. All will soon be engaged in the hectic task of reproduction. Standing on the North Norfolk coast with eyes watering in the teeth of yet another spring gale does make you wonder why these small vulnerable birds make the arduous journey from mainly warm and food rich parts of Africa to spend a couple of short summer months with us. It can’t be the scenery, as lovely as it is, it certainly isn’t the weather, so what drives these lightweight bundles of feathers to risk life and limb to seek out that small copse, patch of reeds or windswept moor and set up a seasonal home here in the UK? Beats me!
I’m joking of course. There are very clear and logical reasons for this migration, since nothing happens by mistake in the natural world. The answer lies in the long hours of daylight which affords the maximum opportunity to exploit the super abundance of insects that proliferate in our short but bountiful summer. What better way to ensure the needs of your voracious offspring can be met? That’s all well and good, but surely there is plenty of food in Africa? Well, let’s dig a little deeper and the purpose for this northwards dispersal becomes more reasoned. Think about how difficult it would be if the whole population of a certain species was vying for nesting sites and food in a limited geographical area. Competition would be immense and reproductive success would suffer as a consequence. Surely better then to spread over a much larger area, i.e. Europe, Scandinavia and even the Arctic to take advantage of lush and widespread vegetation, ample nesting sites and an emerging food source where each bird stood a reasonable chance of finding territory and breeding successfully. Similarly a concentration of breeding birds in a small area would inevitably attract a concentration of predators with the result that many young would never make it to the fledging stage. Such a waste of energy and resources could have a serious effect on the population of some species, so better to disperse widely and make predators work harder for their meal. Other reasons revolve around minimising the likelihood of disease or local climatic extremes decimating a densely packed population. When these issues are factored into the life of a bird it does make sense to leave the oppressive heat of Africa behind for a few months and return when it is more temperate and has its own fresh supply of insect fodder.
It is tempting when looking at our grey skies and wondering when we can actually turn off the central heating to muse that birds have got it all wrong, but in fact they have it all worked out. Better still it gives us a chance to make acquaintance with these lovely jewels anew each spring and use them to chart the passage of our own lives as we move through the yearly cycle.
Anyway, a few pictures of some of our local migrants to cheer us up during this somewhat disappointing spring.
WheatearThis is a female seen at Cley last week. These perky lovers of open ground
begin to arrive in late March and move through the county until late May.
Later birds are quite often of the larger, deeper coloured Greenland race,
and there has been several of those seen recently. Formerly a widespread
breeder hereabouts they are nowadays mainly confined to the uplands of
the north and west although a few pairs cling on in Breckland.
BlackcapWe saw many of these lovely songsters migrating through Israel a couple of
weeks ago. This one was photographed at RSPB Strumpshaw Fen yesterday.
Our birds will winter in sub-Saharan Africa and begin to arrive
back here during April. Generally milder conditions over the last 30 years together
with an abundance of artificial food supplies has allowed a growing population
to overwinter here in the UK although it is believed these birds originate from
Germany and other central European countries. Interestingly, these birds
have an easier return migration, arriving earlier than those making the trip from
Africa. This allows them to select prime breeding territories and raise more young.
The young are genetically programmed to follow the adults migration route thus
increasing the numbers making the journey to our shores. Research has shown that
these birds are already showing signs of having shorter wing feathering (no need for
long flight feathers if you aren't flying far) and could be evolving into a new sub-species.
WhitethroatSeveral of these distinctive warblers are delivering their scratchy songs
from bramble patches along the coast road at Cley.
Reed WarblerI surprised this one searching for insects along the boardwalk at Cley.