The science of Big Garden Birdwatch

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Martin Harper's blog

I’ve been the RSPB’s Conservation Director since May 2011. As I settle into the job, I’ll be blogging on all the big conservation topics and providing an inside view of our conservation projects. I hope you enjoy reading it and feel inspired to join in t

The science of Big Garden Birdwatch

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On Saturday morning, before taking my daughter to ballet, I shall grab a coffee and sit for an hour staring at my garden.  I'll join the half a million or so that will take part in Big Garden Birdwatch.   The kids and I will take turns with the binoculars and the laptop to spot birds and upload our results. 

The weather forecast sounds perfect and I am hopeful that the Long-tailed Tits that have been frequent garden visitors this month decide to make an appearance. 

The survey is now in its 36th year and is the largest of its kind.  We have, over the years, collected a huge amount of data.  I often get asked whether the data collected are valid and meaningful, so I thought I'd share a conversation that I had with Daniel Hayhow, the RSPB scientist who has assumed responsibility for managing the survey.  

This is what he said...

"Holding the largest, longest running citizen science dataset in the world offers great potential, but enormous challenges especially in terms of analysis and computation.

Colleagues in the RSPB Centre for Conservation Science have already used these data in a number of ways and are exploring future uses and application of this vast resource.
 
The good news is that there is a good correlation between the trends from the BGBW with those from the BTO/JNCC/RSPB Breeding Bird Survey (BBS) - the main scheme for monitoring the population changes of the UK’s common breeding birds. This correlation works for species you would expect - for instance demonstrating the increase in woodpigeon abundance (742.5% increase in BGBW gardens 1979 - 2014) in the UK and the more recent decline in numbers of greenfinches (70% decline in BGBW gardens since 2005 (-44% decline since 1979).  This gives us confidence in the results collected by hundreds of thousands of citizen scientists.

 Specific questions can also be answered about species which are not covered by other monitoring schemes. For example we can look at the geographic spread and increasing numbers of wintering warblers.  For example, blackcaps have been increasingly recorded in BGBW gardens. It is thought that climate change and possibly increase in people putting out bird food in gardens means that instead of migrating to the Mediterranean and North Africa Blackcaps have been able to increasingly overwinter in the UK  as far North as the Outer Hebrides.

The type of birdfeed participants use for their Birdwatch is of great importance and allows us to explore relative merits of different types of food. Previously, scientists have used BGBW data to look at the increasing number of Redpolls in gardens in relation to niger seed. Using the 5 years of data available, we found that there was no overall relationship between Redpoll numbers and niger seed. This suggests that the increase in Redpoll numbers in gardens is not primarily driven by increasing niger seed provision. However, in the single year where numbers of Redpoll were particularly high across the country, those gardens where niger seed was provided had higher numbers of Redpoll.  This could have been caused by a combination of factors; an influx of birds from the continent (now considered a separate species), a particularly good breeding season, or a birch seed failure that year meaning birds had to rely on garden food more heavily. Other species on the BGBW radar for investigation include the spread of ring-necked parakeets across the south east.

There are many more questions to explore with BGBW data that are not available through other sources.  For example, we could do more to explore the importance of garden food provision, assess the influence of different garden features (trees, shrubs, ponds etc), understand the use of gardens in relation to features in the wider area eg distance to woodland/farmland etc.

It will also be valuable to revisit some of the questions above  with data from subsequent years to see how patterns may have changed.

And now BGBW asks questions about sightings of other wildlife – mammals (currently: red squirrels, grey squirrels, roe deer, muntjac deer, fox and badger) reptiles and amphibians (including: frogs, toads, grass snakes and slow worms). Again the scale of the data collected via BGBW makes these sightings extremely valuable and we’ve been delighted to work with partners (Mammal Society, Amphibian and Reptile Conservation and People’s Trust for Endangered species) sharing the data.  As the data set grows we hope to use it to improve our understanding of how distribution of these animals changes over time and how they use our gardens."

I am keen that we make the best use of the data that we generate over this weekend and in future years - so I expect to be keeping Daniel quite busy.  So, while you are drinking your morning coffee and watch the birds in the garden this weekend, be reassured that the data you collect will be put to good use.  And, just as importantly, I hope that it encourages more people to take an interest in wildlife in their garden and, who knows, perhaps even inspire the next generation of conservation scientists.

Have a great weekend.

Photo credit: Nigel Blake (rspb-images)

Comments
  • I would like to see the data presented in more ways. For example rather than just 'sparrow is most numerous', which bird is found in most gardens - my bet would be blackbird.