Rachel Crookes
Summer has finally arrived – wildflower meadows are blooming, bees are foraging in the flowerbeds and many bird species are well into their annual cycle of laying eggs and rearing chicks. In many garden nest boxes, the eggs of small birds such as tits and robins will have hatched, with diligent parents spotted darting back and forth from the nest box hole with caterpillars to feed their hungry brood. The late spring and early summer months are also a busy time for the network of 750 British Trust of Ornithology (BTO) volunteers that monitor these nests and those tucked away in bushes, reedbeds and treetops.
The BTO’s Nest Record Scheme gathers information on the breeding success of the county’s birds by following the progress of individual nests. The scheme was established in 1939, and from its small beginnings it now receives around 35,000 records a year from its volunteer recorders. The project’s data gives invaluable information about the county’s breeding birds, helping to track changes in breeding success and correlate these with changes in the wider environment.
Even within a garden nest box, a lot of useful information can be captured to inform a bigger picture across the country. Typically blue tits and great tits will take advantage of a standard 32mm hole nest box, filling the bottom of the box with moss before lining a central cup with warmer feathers and fur. Recorders will take their first peeks inside the box to determine the laying and incubation periods – blue tits will lay between 8-12 eggs per brood, which the female will sit on for around two weeks. At the start of May, the chicks hatch and recorders can note the proportion of eggs that have successfully hatched - each chick can eat 100 caterpillars a day, so to feed a brood of ten, adults need to find as many as 1,000 caterpillars a day! After a month of growing, the chicks will have developed feathers, and parents will call to them outside the box to encourage them to take their first journey out into the world – the recorders will note the number of chicks present at the end of the nestling period, and the final date all leave the nest.
Tit chicks in nest box
Blue tit chicks almost ready to fledge
Beyond the garden, recorders can search for and gather data on nests in other locations – house martins live in mud nests below the eaves of buildings, dunnocks and wrens will nest in dense scrub and goldfinches, and waterfowl and wader eggs can be found in the reedbeds that surround ponds. Across farmland and estates, raptor boxes erected for barn owls and tawny owls look out over grassland expanses, their chicks only accessible using tall ladders. Many species such as robins and blackbirds will have more than one brood in each breeding season, laying further clutches of eggs after their first chicks have fledged. Some rarer bird species have additional legal protection, meaning a license is needed to approach and monitor their nesting sites.
Collecting nesting data has seen how climate change has been affecting our resident species – chick hatching is generally timed with their species’ preferred food source’s peak in abundance (e.g. caterpillars for blue tits), but unpredictable changes in the weather can see shifts in the timings of annual events, with knock-on effects. For example, 2021 saw an early but cold spring, which delayed egg laying dates by over a week in some cases and resulted in a particularly poor breeding season (BTO, 2024). The Nest Record Scheme’s data has also been important in understanding drivers of population changes – in 2014 a study was published using data collected from the scheme and the Garden Bird Watch project, which shed light on factors behind the decline in house sparrows in rural and urban areas.
If nest recording sounds like something you’d like to get involved with, the BTO have two schemes that budding bird recorders can sign up to;
• Nesting Neighbours – for those who are new to nest monitoring and want to record a small number of nests in the garden.
• The Nest Record Scheme – for those who want to monitor a network of nests in your local area, erect and monitor boxes in your local spaces, or become a highly skilled nest finder.
There are also opportunities for people to become trained bird ringers – here volunteers are trained over the course of several years to ring adults and chicks either on nests or through other capture methods such as mist netting. This can give even more detailed information about population dynamics, such as the migration of birds in and out of an area.
The Nest Record Scheme allows those passionate about birds and wildlife in their garden to input into wider citizen science proects that produce valuable data to conservation organisations. This scheme along with other projects such as the Big Butterfly Count and the National Plant Monitoring Scheme allow us to better understand how species are responding to environmental changes, and what we can do to mitigate the impacts of our changing climate.
References
• British Trust of Ornithology – Preliminary report on the 2021 breeding season. Accessed 02.04.2.24 www.bto.org/our-science/projects/bird-ringing-scheme/ringing-surveys/constant-effort-sites/ces-results/preliminary-report-2021
• Catriona A. Morrison, Robert A. Robinson, Dave I. Leech, Daria Dadam & Mike P. Toms (2014) Using citizen science to investigate the role of productivity in House Sparrow Passer domesticus population trends, Bird Study, 61:1, 91-100, DOI: 10.1080/00063657.2013.874975
