Leaving work the other afternoon my attention was caught by the sight of two dozen Jackdaws riding on the breeze. There is nothing unusual in this you might think but the flock was loose in its formation and made up of discernable couples. Each pair of birds was separated from every other pair by a certain amount of airspace and it was clear that these were breeding partners, possibly displaying in the sky above the nest sites soon to be occupied.
In fact, there has already been a certain amount of work on the nest sites used last year, with birds collecting new nesting material in the form of twigs and clumps of fur, brushed out from winter coats by the dog owners who walk along this part of the river. Jackdaw nests are untidy in their construction and can be surprisingly large. The birds seem to adopt an approach whereby they keep adding sticks to the nest cavity until it is full and ready for lining with softer material. I remember once checking an old Barn Owl nest site in the attic of a ruined cottage out in the fens; the owls were no longer there but the Jackdaws had moved in and constructed a nest that was at least eight feet across and four feet tall. It was a truly amazing construction.
Although the sight of these birds flying in tandem had suggested to me that the pairs had only recently formed, this was almost certainly not the case. New pairs probably become established in late autumn or early winter and you can see Jackdaw pairs in pretty much any month of the year. This might suggest that pairs remain together for life but changes in partnership do occur from one year to the next. Birds may continue to use established nest sites over long periods of time and it is easy to see why such large nests can accumulate in some cases. Jackdaws are very adaptable when it comes to the choice of nest sites, although very few end up constructing a nest out in the open. Most nest in cavities, either natural holes in trees or those accidentally created by humans. Jackdaws can be found nesting in disused mine shafts, church towers, chimneys and even nest boxes, specially erected for their use. They are gregarious birds and, if conditions allow, you will often find several pairs nesting in close proximity
Since Jackdaws can initiate egg laying from the beginning of April, they are one of the first birds to really get going with the arrival of spring. Most pairs, however, start in the second half of April so expect to see some collecting twigs over the next few weeks.