On Friday morning I finished the Nightingale survey that I
volunteered to do on behalf of the BTO. I’ve really enjoyed doing it; here’s
some background about it and thoughts on how it went.
The last survey on this scale was carried out by the BTO in
1999. A lot has changed in 12-13 years; elsewhere in the countryside numbers of
similarly iconic migrant birds such as Turtle Doves, Cuckoos Yellow Wagtails
have plummeted. This survey will help determine how nightingales have fared
since then, making 2012 an important year for this amazing bird.
Methodology
For the survey I was given two tetrads (or 2km x 2km squares)
to cover on an area of the North Downs near my home in Kent. These were squares
that had previously had nightingales recorded. The aim of the survey was to
record the number of singing males in each tetrad. An additional important
factor to consider was habitat. The BTO survey methodology stated that each
site was to be paid a minimum of 2 visits, between 21st April and 14th
May, between dawn and 8.30am in fair-good conditions. Any nightingale
encounters were to be annotated CBC fashion (the standardised recording of a
bird’s activity eg singing male, in flight, with nest material etc) on
accompanying sample OS maps. Nightingale territories (likely nest sites with at
least one male in song) were also required to be logged in a results table. Besides
the two daytime visits, two nocturnal visits were suggested after 18th
May, between midnight and 3am, on any squares which logged males in the daytime
surveys, to locate any males still singing. The theory behind this is that any
males singing at this time are likely to be non-breeders, or those without a
mate. Interesting - presumably this distinction then gives a far more accurate
overview of breeding populations. I was really hoping to get some birds on the
daytime visit so I could go for a midnight ramble on the downs!
Survey
I visited each site a total of three times. I made an
initial visit (as suggested) to refresh my memory, check out paths and habitats
etc. These visits were worthwhile and revealed that both squares did
contain suitable habitat but in varying amounts. I highlighted these areas on
the map for later reference. The habitat assessment is important because nightingales
are known to favour certain areas, particularly low, dense scrub with some bare
ground and young growth woodlands/thickets with canopy cover. One square in
particular looked really promising as it held a large disused quarry with steep
sides and ample dense vegetation. I knew access would be impossible but
reckoned I would be able to cover most of the perimeter from footpaths and some
minor, well-intentioned trespassing.
For my two subsequent ‘daytime’ visits my approach was a
simple one – looking and listening (hard!) Generally, each square had large
areas that were clearly NOT suitable Nightingale habitats; arable fields, maturing
Oak/Ash woodlands with little understorey and to these I paid little more than
cursory ‘birdwatching’ attention. Instead I focused on the ‘key’ areas,
spending as much time as necessary walking, stumbling and just standing still
to listen. By and large, each visit took around an hour and a half. One major
downside of the visits was the weather. I know it’s largely been the same
everywhere but the conditions were not really favourable. I didn’t have the
luxury of picking and choosing days, I was limited to a few and had to take the
best I could. It rained to some degree on 2/4 visits and on all bar one, the
conditions were cool, overcast with some breeze – not great for singing birds!
I was thankful of the decision to extend the survey period by several days.
 |
A view from the Downs looking South East towards Holborough and Snodland.
Much of tetrad incorporated arabale fields like this - an unsuitable habitat for nightingales |
 |
| Young trees, scrub and brambles - a much better example of Nightingale habitat... |
 |
| ...but access was difficult. |
Results
So what did I find?
Well, for all those lost hours under a duvet, all those
miles walked and all those hopes raised, unfortunately neither square recorded
a single Nightingale. There was a smattering of Yellowhammer, Lesser
Whitethroat and Willow Warbler but not quite what I was looking for. It’s disappointing,
however I think it’s worth noting two things. The first is that just because I
didn’t find any, it doesn’t mean definitively that nightingales are not present.
There are a number of variable factors to consider, including the weather,
which hardly helped. Secondly, the result is still statistically significant.
Simply put – there are no nightingales where there used to be. Once submitted
that will play a part in establishing the local, regional and national trend.
When the results from all the tetrads are in, the BTO will be
able to analyse the data and gain some understanding of the abundance, distribution
and habitat preferences of nightingales in the UK in 2012. Having swapped notes
with other volunteers in the area, the first indication is that sadly, my
result is in-keeping with the general trend for our patch of the North Downs. National
results will follow but this raises the question that why, if nightingales were
present here in 1999 or thereabouts, they aren’t here now?
Assuming there is a local decline, the challenge will be
looking into to the causes behind it. Are fewer nightingales returning to Kent
because of conditions in their sub-saharan wintering grounds or through the
hazards of their 5000km annual migration? Or is the problem closer to home, in
their breeding grounds of southern England? Is it a combination of all these
factors?
Once they leave our shores in the summer, the fate of the
birds is still relatively unknown. This is the focus for long term research that
may yield crucial answers. Closer to home though, attention must focus on conditions
in our countryside.
- The practice of coppicing
which traditionally took place across the Downs has virtually ceased in
the last few decades (although I’ve read that it is returning in places).
This activity, whereby trees are cut to a stump and routinely harvested on
rotation across a number of years, was responsible for creating the kind
of dense young growth habitat favoured by nightingales. As coppicing has
declined, many coupes and woodlands have suffered a loss of biodiversity,
largely through excessive canopy shading. With little light reaching the
floor, shrubs and brambles are outcompeted resulting in a limited
variety of structure. The decline of traditional woodland management also extends
into that of farmland and hedgerows.
- Similarly climatic changes
may be affecting nightingale populations in the area. Despite a wet spring
in 2012, this was preceded by drought warnings and exceptionally dry seasons
in previous years. For a bird that has traditionally shown preference to
habitats near water bodies, a contracting range may be a result of this.
The Hoo Peninsular in Kent, an area which meets this requirement in
places, appears to be a particular stronghold for the species.
- More recent studies have
looked at the impact of deer browsing, particularly Muntjac deer, on
woodland bird species. This seems to an increasingly important factor in
places although I’m not aware of that being a problem in this particular area.
From the first visit, my general feeling was that I would be
unlikely to find any nightingales. That was based on my own basic knowledge and
experiences of them. Still, I really enjoyed the surveys; a dawn ramble across
the gentle chalk ridges and fields of the North Downs is hardly a wasted
moment. Whatever the outcome of this survey, we’ll be in a stronger position
for knowing – and in time, perhaps we’ll be able to address the changes and
allow this iconic bird and its wonderful song to once more become a feature of springtime walks on the
North Downs.
Read more about the survey
here
Above sound clip recorded on my phone at RSPB Northward Hill, Hoo, Kent, 27th April 2012
Thank you to Andre Farrar for his comment via Twitter
