Two broods are better than one

Hazel Evans, NRS secretary writes:

Studies in Europe demonstrate that Great Tits have the potential to produce two broods per season; a recent study of populations in The Netherlands showed that over 50% of birds were double-brooded in the 1960s, though this number has been declining as the climate warms. Despite this observation, records of double-brooded Great Tits are still relatively scarce in the UK – is this because it is truly a rare behaviour or because we’re so used to thinking of them as single-brooded that we don’t often check our boxes after the first chicks have left?

Robin and Moya Myerscough from Norfolk have been keeping a very detailed log of the comings and goings at their garden in nest box during 2016. A female Great Tit began laying on 6th April and completed a clutch of nine, which hatched on the 27th. Unfortunately two chicks died but the remaining seven fledged successfully at 08.15 on 17th May.

Female Great Tit collecting nesting material. Photo taken by Jill Packenham

These observations constitute a great record for the BTO’s Nest Record Scheme but nothing seemed particularly out of the ordinary. However, by 2 pm an adult was bringing in fresh nesting material and it laid the first egg of a second clutch the very next day.  This in itself is unusual, but a gap of less than 24 hours between attempts seems amazing. Great Tit fledglings are heavily dependent on their parents for about a week after leaving the nest but it is possible the female was able to juggle these responsibilities with laying of the second clutch, given incubation does not commence until the penultimate egg is laid.

Great Tit removing a fecal sac. Photo taken by David Waistell

In truth, while it seems rapid, we don’t really know just how this observation compares to the typical interval between broods, but the widespread use of nest box cameras has the potential to significantly increase the amount of information we are able to collect. Whether you own a camera or not, it’s worth keeping a close eye on your nest boxes over the next couple of weeks to check for second broods – remember to submit records of any attempts you find  to  the Nest Record Scheme or Nest Box Challenge.

Happening in a box near you

National Nest Box Week kicks off every year on Valentine’s Day. It’s a week where the BTO encourage members of the public to put up nest boxes in their gardens. Our garden birds are just starting to prospect nesting sites in preparation for the approaching spring, so the sooner you can get a box up the better, whether you build it yourself or buy it from the garden centre.

Great Tit - David Waistell

There are increasing concerns that the availability of suitable nesting cavities is falling as old trees are felled and houses are repaired, so erecting a box could make a real difference to a pair of birds in your garden. However, the real conservation value of erecting a box is the opportunity it provides to safely record the progress of the nesting attempt, looking inside at intervals to count the number of eggs and chicks and submitting data to one of the BTO’s nest monitoring schemes. The benefits of your monitoring efforts will be felt well beyond the confines of your garden, benefiting national bird populations by helping conservationists to understand the impacts of climate change and urbanisation on the number of young reared and therefore, ultimately, on population trends.

Blue Tit nest - Hazel Evans

Nest Box Challenge  (NBC) is an on-line monitoring survey focussed on gardens, with the ability to record data on both box-nesting birds, such as Blue Tits, and open-nesting species, such as Blackbirds and Woodpigeons.  The Nest Record Scheme (NRS) collects more detailed data on all nesting species across a wide variety of habitats. People are understandably wary of approaching nests, but there is a very large body of research showing that the contents can be examined without a negative impact on the outcome of the attempt, as long as the guidelines set out in our NRS Code of Conduct are followed.

The number of people nest recording in the UK has never been higher, with almost 1,000 volunteers monitoring over 45,000 nesting attempts in 2014 alone through NBC and NRS. The Nest Record Scheme is now in its 76th year and in that time over 1.35 million nest records from 232 different species have been sent in, creating an invaluable and unique record of the UK’s breeding birds. These data are used to generate annual trends in laying dates, the number of eggs produced and the number of chicks reared, which are published each year in the BTO’s BirdTrends report. By analysing nesting data in conjunction with survival data generated by bird ringing, we can assess the contribution that changes in the number of fledglings produced makes to national population trends.

Blue Tit fledgling - Tommy Holden

By far the most common inhabitants of our garden nest boxes are Blue Tits and Great Tits. They have adapted so well to living in our man-made constructions that we receive thousands of records every year; so do we really need any more? The answer is a resounding ‘Yes’, as the better the coverage, the more we can explore the degree to which birds responses to changes in the environment vary between regions and habitats. Your help is vital in continuing to build on this amazing dataset, so why not make 2015 the year you start monitoring nests?


By Hazel Evans, Nest Record Scheme secretary