In the first 20
months of the BTO's Cuckoo Tracking Project we have learned a huge amount about
the migratory journeys of Cuckoos. With them, we have experienced summer
deluges, Spanish drought, the hazards associated with migratory journeys and
the hunt to keep up with seasonal flushes of insects in Africa.
Migration for Cuckoos appears to be an even more risky business than we
expected and, even with only two groups of Cuckoos to look at, it is obvious
that there can be huge between-year differences in the challenges they face.
All five birds
ringed in 2011 were still transmitting data in December of that year but, of
the 14 males that left their breeding sites in 2012 only five were still
transmitting in December, one being Chris, now providing a second year's worth
of data. At least two of the losses this year (Roy and Mungo) are, we think,
associated with tag failure rather than the death of the birds. Given that
Cuckoo numbers in the UK
are declining, one of the key aims of the project is to try to understand the
circumstances that may be contributing to increased mortality. Knowing how and
when we lose marked Cuckoos is as important as understanding their migratory
journeys.
The Class of 2011
In the first year
of the project we tracked five male Cuckoos, hoping that (in line with
estimates of survival from ringing) two or three would complete the round trip
to their mystery wintering locations in Africa.
We were surprised and delighted when all five made it as far as Africa and
astounded that they revealed new information about early departure dates and a
new migration route through Spain
and western Africa. The return journey was
trickier, with Clement being lost soon after heading westwards from the Congo forests and Martin succumbing in Spain.
Particularly poor weather may well have been to blame; we know that there were
unseasonable hailstorms in the exact spot where we lost Martin, for instance.
Kasper's tag is thought to have failed soon after he completed his northward
desert crossing but Chris and Lyster were still sending signals when they
returned to Norfolk ? which
was exciting news for everyone involved.
The Class of 2012
Given its
success, we expanded the project in the summer of 2012 to include males from Scotland and Wales. We were keen to discover
whether Scottish birds, whose numbers do not seem to be declining, might have different
migratory strategies (which may just be the case ? read on!)
and to look for east?west differences between Norfolk
and Wales.
BB, Chance, Mungo, Roy and Wallace were tagged
in Scotland, while David,
Indy, Iolo and Lloyd began their journeys south from Wales. John and Reacher joined
Chris and Lyster as our East Anglian representatives.
Most of the Class
of 2012 failed to make it to the African wintering grounds ? in
complete contrast to the Class of 2011. Hopefully, as we analyse this year's
data, and start to add data from future years, we will better understand the
rules of the game of 'snakes and ladders' that Cuckoos face each autumn, winter
and spring on their 10,000-mile round trips. The summer of 2012 was wet ? very
wet, with a real dearth of insects ? and we were concerned that migratory birds
may be in poor condition when it came time for departure. This was not the last
of their problems, however, as we would see over the autumn period. We can only
speculate as to what proportion of the losses was associated with conditions on
the ground in southern Europe and how much was due to poor preparations in the UK.
In 2011 migration
was relatively straightforward, but in 2012 there were a number of cases where
we saw birds return northwards, presumably because they could not find food.
Lloyd sampled sites in northwestern and northeastern Italy
as well as in southern and southwestern France
before making it across the Mediterranean, while John gave up on Spain and returned to France. We guess that Indy's U-turn
in the middle of the Mediterranean, as he flew back to northern Italy, must
have been associated with running out of resources and going back to his last
known feeding ground to refuel.
We were surprised
when, in 2011, two of the tagged birds successfully used a previously unknown
westerly route through Spain
and western Africa. In 2012, no bird that took
this option completed the journey. John died in France, Reacher died in the
droughts of Granada (Spain)
and Lyster did not manage to complete his journey across the Sahara.
Chris, who was the only English Cuckoo to take the more easterly route, made it
across the desert and south to his wintering area in Congo.
It is early days
and these are small samples but, looking at the routes taken by East Anglian,
Scottish and Welsh birds, there do seem to be some interesting patterns. The
only birds using the western route were tagged in England. Scottish and Welsh birds
overflew the southern coast of the Mediterranean in a broad wave, from Tunisia
to Egypt, with two birds (and possibly a third) using countries east of the
Adriatic as stop-overs, while Cuckoos tagged in England have crossed from
coastal Morocco east through to Libya across the two years. Perhaps the
westerly route is good in some years and not in others? Of the five birds to
reach the wintering grounds, the two birds from Wales are wintering further east
than the remaining English and Scottish birds.
We had also hoped
to include five females in 2012 but they proved very tricky to catch and the
weather was not on our side. BTO scientists managed only to tag one female
Cuckoo above the acceptable weight limit. ?Idemilli.
Unfortunately, the weather in Wales
was uniformly wet at the time that she needed to prepare for her migration. She
is likely to have had a tough time finding enough food to fatten up, which may
explain her presence in a Surrey garden, where
she suffered injuries when attacked by other birds. She was found in a sorry
state and the decision was taken not to leave the tag on.
We do hope we
will be able to tag and track females in the future, but this depends on being
able to catch them, and they do need to be a suitable weight. They also proved
much trickier than the males to lure into the nets. They leave on migration
later than males to make the most of the breeding opportunities. It's thought
they store sperm and continue laying eggs in host species' nests after the
males have left. Juveniles leave even later.
Looking forwards
There is a lot
more to be done to understand Cuckoo migration fully: studying the same birds
in different years (currently only Chris has been tracked in both years of the
project), assessing the effects of weather conditions, gaining a bigger sample
of birds from different regions to look at the routes taken, looking at whether
host species has any effect on migration, the timings and routes taken by
juveniles, as well as females, and much more. However, all of this work
requires funding.
If you would like
to help support and develop the project, you could become a Cuckoo sponsor for
as little as £10. You will receive email updates on the Cuckoos' progress and
your name will be featured on your chosen Cuckoo's blog. If you have already
donated, please consider further support for the class of 2013. We will reveal
the newly recruited Cuckoos in late spring. Find out more about Cuckoo
sponsorship - http://www.bto.org/science/migration/tracking-studies/cuckoo-tracking/sponsor-cuckoo
The Common Cuckoo
The Common Cuckoo - Cuculus canorus ? formerly European Cuckoo is a widespread summer
migrant to Europe, Asia and winters in Africa. Breeds across Eurasia, in the
non-breeding season it heads south it to sub-Saharan Africa.
Description
Adult males are
slate-grey with barred underparts. The iris, orbital ring, the base of the bill
and short legs and feet are yellow. Grey adult females have a pinkish-buff or
buff background to the barring and neck sides. Rufous phase adult females have
reddish-brown upperparts with dark grey or black bars. Common Cuckoos in their
first autumn have variable plumage. Some are have strongly-barred
chestnut-brown upperparts, while others are plain grey. Rufous-brown birds have
heavily-barred upperparts with some feathers edged with creamy-white.
Call
The male's call,
goo-ko, is usually given from an open perch. The female has a loud bubbling
call.
Food
Diet consists of
insects, especially hairy caterpillars.
Breeding
Common Cuckoos
first breed at two years old. The Common Cuckoo is a brood parasite. It lays
its eggs in the nests of other birds. At the appropriate moment, the hen cuckoo
flies down to the host's nest, pushes one egg out, lays an egg and flies off.
The whole process takes about 10 seconds. A female may visit up to 50 nests
during a breeding season. The chick hatches after 11?13 days. It methodically
evicts all host progeny from host nests. It is a much larger bird than its
hosts, and needs to monopolise the food supplied by the parents. The chick will
roll the other eggs out of the nest by pushing them with its back over the
edge.
Conservation Status ? Least concern
Not threatened,
in fact it is widespread and common in Southern Africa. In the UK a marked
decline in numbers.
Birdwatching
Cuckoos can be
seen throughout the UK, but are especially numerous in southern and central
England. Adults arrive in late March or April and depart in July or August,
with young birds leaving a month or so later.
Ask Aves Birding Tours/Safaris/Adventures to
create a custom tour for you or book on one of the following scheduled Aves Birding Tours/Safaris/Adventures:
-
Aves Eastern Cape
Birding Tour / Safari /Adventure.
Aves Highlands /
Tembe Birding Tour / Safari / Adventure.
Aves KZN Birding
Tour / Safari / Adventure.
Aves North East
Birding Tour / Safari / Adventure.
Aves North West
Birding Tour / Safari / Adventure.