Update on our bird boxes
RGCG has 21 bird nesting boxes dotted in trees around the Green.
Sponsored by Redland and Cotham Amenities Society, we attached sixteen box in trees in the winter of 2019/2020. Four were added in autumn 2021, sponsored by a private individual. In April 2023, a further private sponsorship enabled us to add our 21st box.
We have a mix of boxes, to cater for a variety of different species, ranging from blue and great tits, nuthatch, house sparrow and robins, wrens, song thrush and blackbirds. More about the boxes can be read by following the links above.
We survey our boxes each year (after the end of the breeding season) so that we can monitor their use. At the same time, we clean out last year's nests. Birds make fresh nests every year, and cleaning the boxes both helps the birds (saving them the effort of removing old and used material) and gets rid of any build up of pests and parasites.
In addition, this year, many boxes needed adjusting, as it is now three years since the first set boxes were installed. Quite a few of the faster growing trees have increased in girth, and so the box fixings needed adjusting (and sometimes replacing) to avoid them getting grown over. To clean and adjust the boxes, they were lowered to the ground using a rope and pulley system controlled from the ground, or just handed down when it was easy enough.
The other improvement made this year was to refresh the faded box numbers, to aid in box identification.
Last year, ten of the eighteen boxes (excluding the sparrow terrace and the starling box) had full nests, and two had incomplete nests. All four of the 28mm holed boxes were used and six of the ten with 32mm holes were used. We assume that, as in previous years, they were all used by blue and great tits.
Once again, none of our four open-fronted boxes (intended for wrens, robins, blackbirds and song thrush) were used. The sparrow terrace and the starling box were also unused.
Overall, 55% of our boxes were used for nesting, which is a slight improvement on the previous year (50%) when we also had two fewer boxes suitable for the tit family. It it wouldn't necessarily be expected to have a nesting occupancy greater than this, as explained below.
This is box 15, and its nest. The box is located in a sycamore tree near the corner of the tennis courts by the bowling club.
It has entertained us in past years because the nest, used by great tits, has been beautifully lined with red wool. This year, slightly less colourful but no less beautiful and skilfully made, the nest was lined with animal hair.
This box, like some others, shows signs of damage, possibly inflicted by a grey squirrel. Thankfully, the woodcrete has proved resistant to such attempts at predation.
The number of nest boxes which can be put up in any given space depends upon a variety of factors. Particularly important are the number and type of trees and other vegetation in the area, the availability of natural nesting sites, how plentiful the supply of food generally is and the presence of predators. In general, there isn’t a minimum distance required between boxes: the birds themselves will decide how close to each other they choose to breed, influenced by the environmental factors above.
The percentage of boxes occupied in any year will vary; however, 60% occupancy is regarded as saturation. Not all boxes will be used for laying eggs and rearing chicks every year, as some may be used for food storage or night time refuges.
Our boxes are a mix of boxes whose holes have diameters of 25-28mm and 32-35mm, open-fronted and other. In the "other" category, we have a sparrow terrace with two nesting compartments and a starling box - much the largest box on the Green, with a nesting hole of 45mm. This can be seen in the maple tree opposite the entrance to the bowling club, and is box number 20.
Guidelines suggest that about 60% of boxes might have holes of 32-35mm, 20% 25-28mm, with the remaining boxes open-fronted or "other". 45% of our boxes have holes of 32-35mm, 25% 25-28mm, with 30% for the remainder.