Sand Martins

Thursday's Guardian Country Diary is about a colony of sand martins that nest in this valley on the banks of the river South Tyne at Kirkhaugh in Northumberland.

These birds are the least familiar of all the hirudines - swifts, swallows and martins - that migrate here to breed in summer. That's partly because they often tend to breed in colonies that are well away from human habitation, unlike swifts, swallows and house martins that all share our buildings. Sand martins can only nest in places where there is an eroded riverbank with sandy soil that's soft enough for tunnelling but firm enough resist collapse.

They are also probably overlooked because they are much less colourful than their cousins, but when it comes to their fast and agile flight they are the equal of all of them. They are almost always the first of the quartet to arrive in Spring, and I've often watched them returning to their nesting burrows March.

Click here for pictures of a colony nesting in the riverbank of a tributary of the Tyne near Corbridge. The great 18th. century naturalist Gilbert White believed that when hirudines disappeared in autumn it was because they hibernated underground. That belief arose because naturalists had seen sand martins nesting in tunnels and assumed that swifts, swallows and house martins could burrow into river banks too during the coldest months of the year. Eventually it was realised that they migrate south in winter but it was only with the advent of bird ringing that their wintering destination in Africa was confirmed.

This is Gilbert White's journal entry for 23^rd. March 1788.

Mr Churton, who was this week on a visit at Waverley, took the opportunity of examining some of the holes in the sand-banks with which that district abounds.  As these are undoubtedly bored by bank-martins, & are the places where they avowedly breed, he was in hopes they might have slept there also, & that he might have surprised them just as they were awakening from their winter slumbers.  When he had dug for some time he found the holes were horizontal & serpentine, as I had observed before; & that the nests were deposited at the inner end, & had been occupied by broods in former summers: but no torpid birds were to be found.  He opened & examined about a dozen holes.  Mr Peter Collinson made the same search many years ago, with as little success.  These holes were in depth about two feet.

This exceptionally trusting individual landed on a fence post close to us, to preen.

That beak has an enormous gape, essential for trawling river flies out of the air as it skims the water surface.

Everything about this bird, with its streamlined shape and scimitar wings, says 'speed'

Bullfinches

Soon after the waxwings moved on a party of bullfinches arrived on the crab apple tree in the garden, to feed on what was left of the shredded fruits, and they have been visiting frequently all day. The crab apples provide a useful diversion from our flowering cherry and pear blossom buds, which these birds tend to feed on from now until spring - although I'd have the bullfinches than the Concorde pears, which aren't very flavoursome. Generations of gardeners have lamented the ravages of bullfinches on their fruit trees. In his Journal entry of February 7th. 1791 Gilbert White, of Natural History of Selborne fame, wrote: "Bull-finches make sad havoc among the buds of my cherry, and apricot trees: they also destroy the buds of the goose-berries, and honey-suckles!" He also implicated greenfinches and, more improbably, grosbeaks in the devastation.

I have a suspicion that it's the seeds in the crab apples that the bullfinches are after, rather than the rotten fruits themselves, which are on the point of disintegration anyway.

As far as I can recall, we usually only have one family party of bullfinches in the garden in winter with just a single male, but over the last couple of days there have been four males in full, magnificent breeding plumage on the tree, which has generated some conflict.

Keeping wild bullfinches in cages has long been illegal but they were once popular cage birds and some bird fanciers learned that if they were fed exclusively on hemp seed their plumage would turn completely black. Birds can't make red or yellow carotenoid pigments, which come completely from their plant diet, either directly (from pear buds, in the case of bullfinches for example) or indirectly from eating animals that eat plants (from caterpillars in the case of blue tits), so it must be that hemp seed is low in these pigments and high in other darker ones that accumulate in the birds' feathers. But, as Gilbert White noted, all bullfinches are not equally susceptible. Here he is again, in his Journal entry for December 9th. 1781: "George Tanner's bullfinch, a cock bird of this year, began from its first moulting to look dingy; and is now quite black on the back, rump and all; and very dusky on the breast. This bird has lived chiefly on hemp-seed. But Dewey's and Horley's two bull-finches, both of the same age with the former, and also of the same sex, retain their natural colours, which are glossy and vivid, tho' they both have been supported by hemp seed. Hence the notion that hemp seed blackens bull-finches, does not hold good in all instances; or at least not in the first year."

If you are interested in reading more of Gilbert White's Journal entries, grouped together by year, they can be found by searching on the wonderful The Natural History of Selborne blog . Click here, for example, for his Journal entries for today, 7th. January between 1768 and 1793, which include mention of the first crossing from England to France by balloon, in 1785.