Brownsea Island's bird and mammal box project

Red squirrel kits in a nest box, Brownsea Island, Dorset | © National Trust / Brian Whitlock

The National Trust staff and volunteer team look after nearly 400 nest boxes across Brownsea Island, which provide homes for a variety of birds, red squirrels and bats. Here we explain a little more about what the rangers and volunteers find on their yearly rounds.

Yearly round-up

Each year, all of the nest boxes are checked in May and September to see if they are in use, and then any repairs are carried out in February. This volunteer led project has been running since 1997.

The team had a very busy five days in mid May this year checking 400 bird, bat and squirrel boxes. They have reported back that plenty of active squirrel nests were found, along with a maternity bat roost containing around 200 bats, three of the owl boxwere being used by tawny owls. There were plenty of bird nests in all stages from eggs to almost ready to fledge young, on the whole it looks like a good year. The full results for 2024 will be published here later this year.

The results from the 2023 box checks are listed below.

Birds

Bird nest records for tit species were down compared to previous years. We recorded 104 tit nests overall, including 39 blue tit, 13 great tit and 1 coal tit nests, plus a high number of ‘unknown’ tit nests. We also found 2 treecreeper nests this year. Tawny owl nests were found in 2 owl boxes in May, with adult owls and eggs seen at both nest sites.

Blue tit chicks in nesting box at Ravenscar, Yorkshire — Blue tit chicks in nesting box | © National Trust Images/Zoe Frank

Red squirrels

Although squirrel boxes are clearly identified (with little porches on the side), squirrels will quite happily hijack any other box they can lay their paws on.

They have been catered for with 55 purpose-built wooden boxes which have proved very popular. As in previous years, we found that red squirrels made use of the owl boxes too, along with various types of bird boxes.

During the 2023 checks red squirrels made use of nearly all the purpose-built squirrel boxes, as well as some owl boxes and bird boxes. We found signs of use in 63 boxes overall, including 1 squirrel kit in residence in May.

Bats

The project also includes around 140 bat boxes, over half of which are hand made from untreated timber.

Many of our bat records are based on the presence of droppings, which indicate that bats have used the boxes. Since 2015, we've found that large numbers of pipistrelle bats congregate in some of our specially-designed wooden bat boxes to form maternity roosts.

In 2023 good numbers of pipistrelle bats were found in 27 boxes across the island, including several maternity roost boxes. Brown long-eared bats were found in a 5 boxes in May and were seen hanging from the roof of the Robert Riggs Hibernaculum in September. We also found Natterer’s bats in 6 boxes. We usually find one or two noctule bats during our checks but none were seen this year.