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 firstname.lastname@example.org). I know that they will be delighted to hear from you.