Black-winged Stilts 2016 from graham white on Vimeo.
There have
been repeated nesting attempts by Black-winged Stilts in the UK in recent years. While spring influxes of stilts into Britain
have largely been driven by dry conditions in south-west Europe, at least part
of the most recent surge of records is also likely to have also been due to an
increase in the nearest breeding populations, particularly in northern France.
It is also clear that some individual stilts are now returning to Britain in
successive years. Although breeding attempts by stilts in Britain are no longer
just one-off events, their overall success has been poor and colonisation is by
no means assured. In 2016, we decided to
try to do something about this. This
blog covers the events of the year, with a fuller account being published in
British Birds in November 2016.
Following the failed breeding attempts by stilts in 2015, we decided to
be proactive and try to maximise the chances of successful breeding in 2016. But where should we focus our efforts given
that stilts could turn up anywhere? We agreed that Cliffe Pools was the obvious
site to work on, given that stilts had nested there in the two previous
years. Our plan was to develop a habitat
so good for Black-winged Stilts that we would draw them in from all
around. Little did we realize the impact
this would have!
The aim was to encourage stilts to nest in a location that contained not
only good chick-rearing habitat but that we could also protect from predation.
Foxes and Badgers are a known threat, but we also wanted to avoid a similar situation
to 2015 where stilts nested on islands where the chicks were predated by
Black-headed Gulls. So, beginning in
autumn 2015, management work started to try and encouraging stilts arriving in
spring 2016 onto a key pool. This
included cutting and grazing vegetation to turn it into prime stilt habitat,
installing a predator exclusion fence around the margins and manipulating water
levels to provide ideal feeding conditions as the likely time for stilt arrival
approached. We sat back and waited.
The first
stilt, a female, was recorded in Sussex on 12th April. The following day, she was on the pool at
Cliffe. A pair of stilts arrived on
17th and a fourth bird the following day.
Two birds left on 19th April but three days later the remaining pair was
joined by a further four stilts – a male and three females. A pair were recorded at Manor Farm in Bucks
on 24th but relocated to Cliffe the following day. Stilts had been recorded at only three other
sites in Britain during April yet 8 or 9 birds had passed through or settled at
our pool at Cliffe! Photographs showed
that two of the males present, and which subsequently nested, had
near-identical head and neck markings to the two males that had nested nearby
in 2015.
Following a
delay during a period of cold weather, two pairs of stilts began nesting inside
the fenced area, with a third pair nesting on a lagoon outside out of it. The
first pair began incubating on 1st May. Based on plumage, the male is assumed
to be one of the males that nested at Cliffe in 2015. A wardening scheme was quickly organised as
soon as this first pair began nesting, and the frequency of Fox control was
increased. This pair diligently took
turns to defend the nest against a wide range of other bird species. As the
hatching date approached, the number of Black-headed Gulls feeding in the area
of the stilt nest began to increase. The gulls were feeding on chironomid
larvae, made more accessible by falling water levels, so we brought in a pump
to raise water levels slightly. This successfully reduced numbers of
Black-headed Gulls in the vicinity of the stilt nest, in the run up to
hatching.
The first
egg hatched on 25th May, and a second two days later. The adults successfully
defended the two chicks against potential avian threats before the effects of
bad weather intervened. At three days old, the youngest and smallest chick
succumbed during a period of torrential rain and cold winds. The first chick
continued to grow well, and became increasingly independent, frequently
exercising its wings. However, on 13th
June, about ten days from fledging, came another period of torrential rain,
this time overnight. Sadly, there was no sign of the chick the following
morning.
The second
pair began nesting on 3rd May, but failed five days after the start of
incubation, when rather bizarrely a male stilt was seen removing and dumping
the eggs from the nest. This pair then relocated across the Thames to South
Essex, a reserve where stilt habitat had been factored into the design and
stilts have turned up every year after the initial wetting-up. However, we were concerned about the
predation risk at this site and we waited to see where they would settle. After
much to-ing and fro-ing around the site, the stilts eventually settled to nest
on 31st May, on an island on Pitsea scrape. A poor choice! This scrape is close to a landfill site, and
consequently surrounded by high densities of Foxes and large gulls. The
reedbeds surrounding the scrape meant it was impossible to install a temporary predator
exclusion fence. A wardening post to
watch over the stilts was again immediately arranged, but the nest failed five
days later. Frustation!
The third
pair started nesting on 14th May but unfortunately just outside the
fenced area. Both birds would chase off
any potential avian predators, including even quite distant Marsh Harriers,
commuting back and forth over the site, and posing no obvious threat.
Consequently, the eggs were frequently left unguarded. The pair lost their eggs
on the night of the 17th May. Although
the cause was uncertain, a Fox was seen close to the predated nest the
following day.
This pair
subsequently reappeared in north Kent, where they were first seen at Higham
Marshes on 7th or 8th June and began nesting there on 11th June. The nest was
in an area where Fox control was already being carried out, and where other
waders had enjoyed a successful breeding season. We again organised wardening
of this pair. The incubation period proceeded uneventfully until, on 4th July, just
before the eggs were expected to hatch, all four eggs were predated by Carrion
Crows.
As
discussed above, the establishment of Black-winged Stilt as a regular breeding
species in Britain is by no means assured, despite the projected changes in
climate. In particular, there are very
few ideal breeding areas in Britain – areas that have appropriate feeding and
nesting habitat, and where predation levels are sufficiently low for stilts to
fledge young. The key measures to
increase the breeding success of pioneering pairs should involve:
- creation and management of ideal feeding and nesting habitat,
- management of water levels to provide optimum feeding and nest protection,
- minimising nest predation, particularly by Foxes, through the provision of predator-exclusion fencing or by lethal control, and
- preventing disturbance by humans, and the theft of eggs, by rapidly implementing wardening schemes.
The RSPB reserve
teams in North Kent and South Essex, together with our contracted wardens,
worked supremely hard to try to deliver stilt success in 2016. Despite what may
seem as a failure with the loss of all five nesting attempts, we have all
learnt a huge amount about how to manage for this colonizing species and this
will no doubt tip the balance fully towards success in future years. Plans are already afoot for 2017!
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