Direct observations at dusk and/or dawn were made of nest boxes, roosting pouches and other cavities. Nest boxes were, again, primarily the domain of Blue Tits, with more than half of observers recording this species – tallying well with the droppings and nest box camera results. Great Tits and Wrens each occupied just over an eighth of nest boxes, with other, less frequent, visitors including Nuthatch, Starling and Tree Sparrow.
Interestingly, patterns in occupancy of roosting pouches and other cavities contrasted sharply with nest boxes. Some 60 roosting pouches were observed, but three out of four were not used, and only Wren used these pouches widely, accounting for 20% of records. Other cavities were different again, housing a wider range of species than either nest boxes or roosting pouches, and a more even ratio of Blue Tits to Wrens – the former accounting for a fifth of records, the latter a quarter. House Sparrows also featured much more prominently in other cavities compared with nest boxes and roosting pouches, representing 10% of records.
Perhaps the most interesting patterns, however, relate to the numbers of each species seen in different roosting sites (see graphs below). The average number of Wrens seen roosting together rose from 6.8 individuals in roosting pouches, to 10.4 individuals in nest boxes, to 17.4 individuals in other cavities. Similarly, the average number of Blue Tits and House Sparrows seen roosting with others of their kind increased from 1.5 and 3.5 individuals in nest boxes, to 2.3 and 6.1 individuals in other cavities, respectively. Therefore, it seems as though other cavities – which may be more variable, sometimes larger, in size than nest boxes or roosting pouches, and may also benefit from the warmth emitted from our homes – might support the greatest variety and numbers of roosting birds in our gardens during winter.
BTO research harnesses citizen science to make breakthroughs in bat monitoring
Bat monitoring has traditionally been challenging, because most species are nocturnal, wide-ranging and difficult to identify. Whilst the National Bat Monitoring Programme run by the Bat Conservation Trust (BCT)...