Treecreepers – nesting and nest boxes
In one section in the wood we have cleared much of the coppice to give space and light to a group of oaks. It slopes down to a small gulley and winter stream, and meets the line of mature Corsican Pines that runs along the wood’s eastern border. There is no better place to sit in the evening with the sun behind us, looking across to the pines. It’s here at this time of day that we are most likely to see a Treecreeper wending its way up the trunk of an oak and along a bough.
Typically, we see the Treecreeper doing just that, making its way in spiral fashion from the base of the trunk and up the tree in a mouselike manner searching crevices for insects. It is not an especially shy bird, but it often seems to move to the other side of the trunk to the observer, and can be a tantalising photographic subject.
They favour broadleaf woodland, particularly oaks, but can be found in conifer woodland. They are usually solitary birds outside of the breeding season.
Why Nest Boxes?
Some species take to boxes easily. Blue Tits, Great Tits, Nuthatches, Starlings etc vie between themselves to take on the space. Others, like Marsh Tits and Treecreepers are not so ready to take one on.
But for relatively common birds like the Treecreeper that seem to have little problem finding a natural site, why trouble to persuade them to use a box? Other than the perhaps selfish desire to be able to watch them more conveniently, organisations like the BTO value information on nesting behaviour e.g. the date of laying and hatching, and number of chicks successfully fledged. It is much easier to collect this type of information from birds nesting in a box than those using natural sites, and records for the Treecreeper are sparse, hence this project.
Nest Box Design
The Treecreepers’ most frequent choice of nest site is behind sections of flaking bark, sometimes with an entrance and exit slot.
A couple of years ago we bought a woodcrete nest box designed for Treecreepers. It has no back, and fixes snuggly to the trunk of a tree so that the tree’s bark forms the back section of the box. There are two small down-facing tubes that act as entrance and exit holes. During the last two seasons Great Tits have used the box, and we are not aware of any interest shown by Treecreepers.
Last year I followed up with the BTO who are trialling a design based on work undertaken by David Francis. David re-created the type of nest site he had seen Treecreepers using, particularly in artificial sites such as wood stacks. He designed a tall, long, narrow box with a slot entrance, and installed five of these in the wood. In the first season one was occupied, and by the third season three had been occupied. Based on this success, the BTO have publicised this design and are interested in follow up results. https://www.bto.org/our-science/projects/nrs/about/treecreeper.
1.8cm slot leading into a 3cm wide cavity 
length of box is 30cm
I’ve built and installed five such boxes. They’ve been in place since early spring, and we’ve monitored three of them with trail cameras. We’ve also recently opened each of the boxes to see if there is any sign of nest building activity. So far there has been no apparent interest, although one box did contain a small amount of fresh moss, which isn’t necessarily the material they would use.
Given David Francis’ experience this shouldn’t be surprising. I plan to keep the boxes in place and construct two or three more so that all potentially good sites (from our perspective) in the wood have at least one box in place, and we shall see what next year brings.