Look out for Tree Sparrows

As I have noted before, the Tree Sparrow is one of those birds that I catch up with from time to time. A substantial and long-term decline has greatly diminished the numbers of Tree Sparrows and it is becoming increasingly difficult to see these delightful birds at many of their former haunts. Every now and then, one will pop up just when least expected. There was the small flock that suddenly appeared in my BTO Bird Atlas square back in February of last year (I have not seen them there since) and more recently two have taken to visiting a garden just around the corner from where I work on the edge of Thetford. The appearance and subsequent disappearance of flocks (and indeed breeding colonies) is well known; it also makes studying them all the more difficult.

Tree Sparrows are thought to have declined because of changes in the way in which we manage our farmland. The move from spring sown cereals, with their associated winter stubbles, to winter sown cereals has removed an important food source during a critical time of the year and it is possible that falling overwinter survival rates may have driven the decline. However, other factors may also have been involved.

One particular aspect of Tree Sparrow ecology that has been of interest of late, is the degree to which birds move away from the breeding colony at the end of the breeding season. In order to examine this, Keith and Ann Herber have been colour marking Tree Sparrows at a breeding colony near Thornham for a number of years. Their efforts have revealed that most birds generally leave the breeding area before the middle of October, returning again during late March or early April. However, Keith and Ann really want to know where the birds go during the winter – do birds spend the winter in the local area or do they move further afield? In order to answer this question, Keith and Ann need sightings of birds carrying colour rings; perhaps you have them visiting your North Norfolk garden during the winter months?

Another aspect of interest to the researchers is why so many breeding birds fail to return to the breeding colony the following year. Have these ‘missing’ individuals failed to survive the winter, or have they chosen to breed at another breeding colony elsewhere.

Do look out for colour-ringed Tree Sparrows, especially up on the North Norfolk coast around Holme, Thornham, Choseley, Ringstead and Titchwell. If you are fortunate enough to see one, do forward the details to Keith and Ann Herber (07785-920044 or email keith.herber@btopenworld.com). I know that they will be delighted to hear from you.

Tree Sparrows a welcome sight

With a patchy distribution and an unobtrusive nature, the tree sparrow can be a difficult bird to connect with. A small colony which frequented a series of farm buildings near one of my regular haunts has been absent over recent weeks and I had been wondering if I would get to see the bird locally this year. It was a welcome sight, then, to bump into three tree sparrows near Middle Harling over the weekend. Walking off a farming estate I caught a soft disyllabic chirp that immediately made me think tree sparrow. Investigating the source of the call, I spotted the distinctive chestnut-capped form of a tree sparrow, tucked into thick cover towards the base of a tree. Two others sat on the other side of the road in the shrubby cover provided by the garden of the estate’s gatehouse. This was a quite unexpected encounter, not least because I have passed this spot many times over the past few years without hearing so much as a chirp.

The tree sparrow has probably undergone a greater decline over the last 30 years than any other British bird. Although widespread across lowland Britain at the end of the Nineteenth Century, its population has been in decline since the 1930s. A slight recovery during the 1960s was linked to an influx of immigrants from the continent but since then things have taken a turn for the worse. The arrival of immigrants late in the year no doubt contributed to the flock of some 1,500 birds which frequented the Eye field at Cley for three months during the 1957/58 winter – a record modern count for the county. Things are very different today, with just a few reliable sites scattered across the county where you can guarantee seeing the species. The areas around Ringstead/Choseley and around the Cressinghams come to mind.

As with other farmland seed-eaters, the decline of the tree sparrow has been linked to changing farming practices. The loss of over-winter stubbles may have reduced food availability and contributed to a potential fall in overwinter survival. However, the species may also be facing problems during the breeding season. Feeding its young on invertebrates, rather than seeds, may leave the species open to a decline in invertebrate numbers. Tree sparrows breed quite late in the year, with most initiating egg-laying during May. Individual pairs may breed through into August and beyond, attempting two or three broods through the season. This means that I will need to return to the gatehouse later in the year to see if these birds are here to stay or just wintering alongside the various finches and buntings that make good use of the area.