This
article was published in the Dorset Bird Club's Newsletter November
2007
High and Dry
in Morocco
I went to Morocco in April
this year with Alan Hayden, Leo Pyke, Mike McKee and Chris Turner
to visit the 'high' Atlas Mountains and the 'dry' stony desert areas
stretching out towards the Sahara proper. We flew from Gatwick and
arrived very late in Marrakech where there was a strike by the local
taxi drivers. A shady character emerged from the shadows and ushered
us to his private car, which unfortunately turned out to be a rather
small Fiat. It was cosy, to say the least, for the five of us but
thankfully it was only a very short drive to the Ibis Hotel where
we were staying.
We ticked off the first
birds of the trip over breakfast, namely Pallid Swift, Little Swift
and House Bunting and then headed back to the airport (this time in
two taxis) to pick up our pre-booked, roomy 4x4. Mike, Chris and Alan
started taking photos of the birds around the airport, whilst waiting
for the car hire desk to open, which attracted the attention of airport
security. We were lucky to get away without getting our optical equipment
confiscated.
The Atlas Mountains rise
to over 10,000 feet and their snow-capped peaks are visible from Marrakech,
70 kilometres away. Driving through the city outskirts were saw White
Storks by the road and Bee-eaters on the wires. We were heading for
Oukaimeden, which is a ski resort in the High Atlas. At lower altitudes
the mountains are lush and green with areas of farmland set among
woodland and scrub. Here we found the 'ultramarinus' race of Blue
Tit, which is bluer and brighter that those in Britain and the 'africanus'
race of Chaffinch, where the males have green backs and much paler
bellies than British birds. The woodlands are also home to Levaillant's
Green Woodpecker, which is very like Green Woodpecker, but with a
black moustache, rather than a black mask on the face. And it's 'tick'
unlike the very distinctive, but un-tickable Blue Tit and Chaffinch.
At higher altitudes the trees faded out revealing Moussier's Redstart
and Black Wheatears hopping about the bare rocks.
€
The birding was excellent
all around Oukaimeden with plenty of mountain species including Rock
Sparrow, Blue Rock Thrush, Rock Bunting, Black Redstart, Chough and
Alpine Chough. Unbelievably as we queued for the ski-lift a Lammergeier
flew down the valley and virtually over our heads only to disappear
without trace. The lack of oxygen made trekking around the peaks hard
work, but there were plenty of Atlas Horned Larks and a few Northern
Wheatears of the Seebohmi race, with the characteristic black face.
We returned to the base
of the ski-lift at 6am the next day to look for one of our key target
species, Crimson-winged Finch, before the crowds arrived. All of us,
except Alan, clambered over the slopes in search of these birds, only
for Alan to find one on the ski-lift office roof! It was soon joined
by several other birds, which posed obligingly to have their pictures
taken.
We left soon after to cross
the mountains and head for the desert. We stopped periodically en
route and picked up species such as Short-toed Eagle, Booted Eagle,
Southern Grey Shrike, Tristram's Warbler and Trumpeter Finch. We had
booked to stay overnight at Le Soliel Bleu, just outside Boumalne
du Dades, which much to Alan's dismay served no alcohol.
We all woke with
clear heads the next day to bird the famous stony desert area around
the Tagdilt Track from 6.15am onwards. The area was brilliant with
plenty of Desert and Red-rumped Wheatears, Temminck's Horned Larks,
Cream-coloured Coursers and just a couple of Thick-billed Larks. We
headed off in the afternoon taking in the Blue-cheeked Bee-eaters
at the well-known colony near Jorf, before reaching the Desert Inn
near Merzouga.
Much of Morocco is
'stony' desert, but close to Merzouga are the Erg Chebbi dunes. Rising
to 150 metres, these sand hills fulfil most people's expectations
of what a true desert should be - you really feel like you are on
the edge of the Sahara proper. The area is also excellent for birds.
Migrants pass through the hotel grounds including Nightingales and
Sub-alpine, Melodious and Bonelli's Warblers. We were also lucky enough
to see Egyptian Nightjar flying over the pool at night! Outside the
open desert is good for Spotted and Pin-tailed Sandgrouse, Hoopoe
Lark and, around the various 'kasbah' buildings, Desert Sparrow. The
scrubby wadis in the area are also good for Desert and Spectacled
Warbler.
One 'kasbah' style hotel
complex is known as Café Yasmina and every few years large
seasonal pools form close to the buildings, bringing a wide selection
of wetland species to the desert. We added Black-winged Stilt, Kentish
Plover, Squacco Heron and Marbled Teal to our lists. The lakes and
surrounding scrub also attracted migrants such as Yellow Wagtail,
Redstart, Sedge and Olivaceous Warbler.
On our way back, we stopped off at a site for Eagle Owl near Rissani.
The site is well away from any road and although a 4x4 can take you
some of the way, you also have to walk. The owls inhabit caves and
crevices in a seemingly never-ending inland cliff-face in the middle
of the desert and we thought that finding them would be difficult.
Fairly shortly after arrival
we managed to find a Brown-necked Raven gliding along the cliff-face,
but the owl proved elusive. Eventually we caught sight of something
large make a very short flight on the cliff face and we rushed over
to check it out. Sure enough it was the owl, which just sat there
in the open giving excellent views.
Only as we walked away
did we notice some stones arranged in the sand spelling out the words
'EAGLE OWL', with a big arrow, pointing at the very point on the cliff
face where we had been looking. Slightly further on there were some
more stones setting out the letters 'LGRE' - that man (Lee Evans)
certainly knows how to make his mark!
I cannot recommend Morocco
highly enough. It has a great selection of birds; fantastic scenery
and the locals are pretty friendly. If you want to see and hear more
why not come along to the slide show I will be giving for CHOG at
7.30pm in the Hengistbury Head Centre on February 8th 2008? A good
selection of bird photographs from the trip also appears on Mike's
website www.michaelmckee.co.uk.
Trevor Warrick -Photographs
© Alan Hayden
This Article was
published in the Dorset Bird Club's Newsletter June 2007
Ringing on
the Weymouth Reserves - a short note
There has been
a long, if interrupted, history of ringing at the RSPB's Radipole
Lake reserve and, with no ringing takin place on the reserve for getting
on for a decade, I have long wanted to re-establish a regular ringing
programme here, not simply because these reserves are, in themselves,
fascinating and rare places but, placed where they are, and with well
established ringing programmes at Abbotsbury and Portland Bill, they
represent an obvious gap in that network and, given there remains
much we can still learn about how birds use this amazing area, these
reserves are well situated to help us in that quest.
I think there
is an old saying that goes something along the lines of 'the longest
journey starts with a single step'. Well, this year, at Radipole,
that first step (albeit a very small one) was taken by the reserve
staff and volunteers and a summer ringing programme was carried out.
It was, as perhaps befits a first step, a slow, timid and unsure start,
but it gathered pace and confidence as the season progressed and the
data we have gathered, albeit small scale (as yet) will allow us to
improve what we do, and hence improve the information we gather, in
future years.
In total we ringed
510 birds, of 20 species, including a rather paltry 7 bearded tits
(more of which later) a few hirundines and, of course, one aquatic
warbler but, not surprisingly, the other reedbed warblers featured
largest amongst the birds caught, with 303 Sedge Warbler (90% of which
were juveniles) and 142 Reed Warbler (60% of which were juveniles).
Although the data are small, so we must be careful in drawing too
many conclusions from them, but it is interesting to ponder the difference
in the age classes of these birds.
Bull and Morgan
suggest the reedbeds here are used by c2,500 Reed Warblers and 6-10,000
Sedge Warblers during any one autumn. From this one might well expect
to find a greater number of sedge warblers (which we did, but not
in the same ratio) and, given that one expects to catch more juveniles
in autumn, we should expect most birds to be young ones (which, for
sedge warblers, they were). I do not know, but I suspect the greater
proportion of adults in the reed warbler numbers reflects the breeding
population. As the data we gather builds it will be interesting to
see if/how that picture changes.
It is also interesting
to look at the habitat mix within which we were catching the birds.
In the same way that fashions change on the high street, ideas about
how to manage specific habitats change as we learn (or, in many cases,
re-learn!) important lessons and I feel this has particularly been
the case with reedbeds. Two or three decades ago the 'style' for reedbeds
was great expanses of swaying reed with little or no variation across
large areas, resulting in large homogenous vegetation blocks. Now
we realise that, as with many other habitats, it is variation that
is the key and, perhaps, the records from the two sets of nets we
put up back that up.
One set of nets
was in the middle of a large homogenous block of reed. In truth the
only structure in the that particular block of reed was the ringing
ride itself! The second set of nets was on the edge of a rich mosaic
of habitats, with reed, sedge/rush beds, open water and wet grassland
all around. As if to prove the point, the second site had 14 (yes
fourteen!) times the capture rate, per foot of net, than the reedbed
site, and for the same degree of effort - do you need any more evidence
that structure and variation in reedbeds is important!
I mentioned earlier
that we did not catch too many bearded tits. It has often puzzled
me where our beardies go and how our population fits in to the Dorset
scene. There have, in the past, been recoveries from Farlington Marshes
and Great Salterns Lake (Hants), Lytchett Bay (Dorset), Berrow (Somerset),
Thurlestone (Devon), Sittingbourne (Kent) and, excitingly, some from
the Netherlands. Most, but not all, of those recoveries were the result
of ringing programmes at those sites. That limits the chances of birds
being recorded so, as has been done in the past, we hope to re-establish
a bearded tit project, using colour ringing, so that we can ask reedbed
sites to keep an eye out for 'our' birds and try and gain a better
understanding of where they are going to. We hope to be able to concentrate
this effort on the autumn, pre-erruption flocks, so gathering as much
information about our population as we can - time will tell, but we
hope to be able to report more at a later date.
Some statistics
suggest that less than 1 in 100 birds ringed will ever be seen again
(hence the need to ring large numbers if you are ever to get meaningful
data) so we were rather excited to catch seven birds which were already
ringed. At least one of these was a 'Radipole' bird, a reed warbler
that was first ringed here nearly 11 years ago, making it a very old
bird indeed! Three young sedge warblers ringed elsewhere were also
very nice, one from Abbotsbury, one from Leighton Moss (Cumbria) and
one, ringed some 621 km away, in Fife, just 7 days earlier! Star of
the show though has to be the aquatic warbler we caught in August,
it was re-caught, the next morning, in Seine-Maritime, France, some
234 km away! This is only one of a handful of Aquatics ringed in this
coutry that have been recovered elsewhere so, as you can imagine,
we are rather chuffed.
Finally, at each
ringing session we re-caught birds we had ringed on previous sessions
(in small numbers) an exercise that can be helpful in establishing
population estimates. Interestingly though, with one exception, all
the birds re-caught were re-caught in the nets they had first been
caught in (if you see what I mean), suggesting little or no exchange
between the two sites, even though they were only a few hundreds of
yards apart as the warbler flies. What was quite simply magical though
was that on the day we caught our first young sedge warbler which
we knew had been born elsewhere, as it was already ringed, we stopped
re-catching our own birds, a clear indication that migration had truly
started.
We have much to
(re)learn about how 'our' birds uses these reserves and how they fit
in to the larger picture, nationally and internationally. The first
step has been taken, and, as our restoration and long term management
plans are implemented it will be interesting to see how that picture
evolves. We will, of course, keep you posted, let's hope the information
keeps flowing as well as it has this year!
Nick Tomlinson
This article was published in Dorset Bird Club's July 2003 newsletter.
TWENTY PREDICTIONS
FOR THE DORSET LIST
Guessing which will be the next bird to added to the Dorset list has
been a constant source of amusement. To get a broad opinion of likely
candidates, I contacted 23 active Dorset birders, of which 18 replied.
Each was asked to list, in order of likelihood, the next ten species
that they considered would be 'New for Dorset'.
Subspecies that
are likely be promoted to full species status in the near future were
included (e.g. Caspian Gull), but not those that have already occurred
(like Hooded Crow), even though they will be technically new to the
Dorset list when upgraded to specific status. I chose to exclude Kumlein's
Gull as it seems highly unlikely that it will be given specific status
and Booted Eagle, as a claim for Dorset has already been submitted
and the bird that toured Ireland and the south-west appears destined
for Category D.
Each correspondents
number one species was awarded 10 points, the second 9 and so on.
In the account, the accumulated points for each species is given,
plus the number of the 18 correspondents that chose it. A total of
49 species were mentioned, the first 20 of which are detailed below.
1st Citrine Wagtail (140 points, 17/18) The clear winner with
78% of the available points. Breeding from western Russia eastwards
across the mid latitudes of Siberia, the range has been spreading
slowly westwards in recent years. Late Aug - mid Oct occurrences are
the norm. Up to 1998 there were 118 records in Britain including a
couple of long stayers at Farlington, indeed 2 occurred in Christchurch
Harbour in 1966 in the days when it still languished in Hampshire.
Although one may make a brief appearance at one of the headlands,
a long stayer is most likely to be found at a wetland like Stanpit
or Lodmoor.
2nd Marsh Sandpiper
(134 points, 15/18) I totalled up the species scores on 7th April
just before I spent a week in Scotland. To my amazement this species
was discovered at Stanpit a mere 3 days later (and fortunately remained
long enough for me to see it the next weekend). With a range from
south-east Europe across Asia, Marsh Sand has been recorded 101 times
up to 1998, mainly in the east but also in all south coast counties
except Dorset and Cornwall. Records span from mid Apr to early Oct,
the Stanpit bird must be one of the earliest on record.
3rd Caspian
Gull (104 points, 12/18) As the BOU has yet to accept Yellow-legged
Gull as a full species, it may seem strange that we are considering
its eastern counterpart as a potential addition to the Dorset list.
However Caspian Gull does differ in morphology, display, choice of
nest site and biochemistry and looks to be awarded specific status
soon. Clearly our correspondents were impressed with its credentials
and awarded it the Bronze medal. It seems that a proportion of the
population leaves the southwest Asian breeding grounds to winter in
northern Germany and the Netherlands. An extrapolation of this route
will bring birds to East Anglia and the reservoirs of the Midlands,
which indeed is where most records have occurred. Undoubtedly one
will be found in Dorset, presumably by a skilled gull enthusiast in
a well watched area like Corfe Mullen tip, Holes Bay or Radipole,
but they are unlikely to become anything but a major rarity. Observers
should remember that unlike Yellow-legged Gull which peaks in late
summer, Caspian Gull is predominately an autumn and winter visitor
to Britain
4th Black Duck
(54 points, 9/18) For along time this species was declining in eastern
North America due it interbreeding and competition with Mallards.
Recently there has been a resurgence in numbers and this has been
mirrored with an increase in numbers in the South-west. With multiple
occurrences in Devon and Cornwall in recent winters, it only seems
a matter of time before one is found here. It needs someone with patience
to sort through thousands of Mallard, to locate what must be one of
the least charismatic birds on the British List.
5th Isabelline
Wheatear (51 points, 11/18) Arriving from its breeding grounds
in Central Asia, Turkey and western Russia in late Sept - early Nov,
there have been 17 records up to 1998, mainly in the east of Britain,
but also several on Scilly or in Wales. The other highly migratory
wheatears, Desert, Pied and Black-eared have occurred here, so it
seems only a matter of time before one is discovered, most likely
on a grassy area on one of our coastal headlands.
6th Cape Verde
or Fea's Petrel (46 points, 8/18) Only accepted by the BOU as
'Madeira / Cape Verde Petrel' it now seems likely that all observations
pertain to the far commoner Cape Verde, or as it more often called,
Fea's Petrel. Most of the 26 records have been in late August and
understandably in the south-west, but a few have occurred in the North
Sea. Do these arrive via northern Scotland or through the Channel?
If any take the latter route then the chance of an observation off
say, Portland, must be good, indeed there has already been a sighting
of a Pterodroma sp. there in recent years. The counter argument is
that south-western specialities such as Cory's and Great Shearwaters
are commoner in the North Sea than in Dorset, indicating that the
Channel route is not favoured by such seabirds.
7th Paddyfield
Warbler (38 points, 9/18) With over 45 British records this south-western
Russian / central Asian breeder looks overdue for Dorset. This bird
might best be identified in the hand but most recent records in southern
Britain have been in reed beds in the late autumn, a time when little
ringing occurs in that habitat. Away from a permanently manned ringing
station (e.g. PBO) the best chance of locating this bird would be
the careful examination of any 'reed warbler' late in the year.
8th Black-winged
Pratincole (31 points, 6/18) There have been 32 records of this
speciality from the steppes of south-west Asia. Like the other two
pratincoles on the British list is highly migratory and as it feeds
on the wing often highly mobile. Unlike the spring arrivals of Collared
Pratincole, the Black-winged is more of a mid-summer to early autumn
visitor. A migrating bird could be found anywhere, but the best chances
of twitching one would be if it settled on a wetland like Lodmoor
or Stanpit.
9th Greater
Sand Plover (28 points, 7/18) It was only 21 years ago when the
first was discovered at Pagham. Since then there have been another
11 records. Like the previous two species it originates from western
Asia, a late autumn / winter arrival date would be likely.
10th Least
Sandpiper (24 points, 4/18) The fourth commonest of the American
peeps in Britain (36 records), the other three (Semi-p Sand, Baird's
and White-rumped) have all occurred in Dorset. Late summer / autumn
occurrences are the norm.
11th Eastern
Bonelli's Warbler (21 points, 5/18) The recent splitting of Bonelli's
Warbler has made the identification of this species somewhat tricky,
with detailed vocalisations as well as subtle plumage characteristics
needing to be noted. This a rare bird in world terms with a population
of only 1% of that of its western counterpart. There have been three
accepted records so far and few more 'likely but not provens'.
12th River
Warbler (19 points, 5/18) Many of the 29 records of this east
European and western Asian have been of singing birds in spring. Perhaps
one will be discovered emitting its 'sewing machine' song from an
area of dense scrub at Poole Harbour or at the north end of Radipole
one June morning.
13th Yellow-rumped
Warbler (19 points, 4/18) Many correspondents felt the need to
include one Yank passerine in their list, and this proved to be the
most popular. Due to the wholesale destruction of habitat in their
Neotropical wintering grounds, populations of many American migrants
have declined sharply in recent years. Yellow-rumps winter much further
north, many within the USA, and may have escaped these depredations.
14th Parrot
Crossbill (18 points, 3/18) Records of this irruptive Fenno-Scandian
species, are understandably clustered in the east, but it has occurred
recently in the New Forest. Clinching a record will need a good view
of the bill, something that seems hard to get on Dorset crossbills!
Could occur anywhere, but Wareham Forest seems the best bet.
15th King Eider
(16 points, 3/18) Once considered only to occur in the far north,
there have been records of females overwintering in Cornwall and a
first year male in Kent in recent years. Careful scrutiny of wintering
Common Eiders in Poole or Portland harbours could pay dividends.
16th Lanceolated
Warbler (15 points, 3/18) Records are increasing as the breeding
range spreads slowly westwards. Fair Isle was always the best site
for this skulking 'sibe' but birds have also been seen in East Anglia
and as close as Hampshire. Most records have been of trapped birds,
perhaps one will be found in PBO's Heligoland trap one October morning.
17th Eurasian
Crag-martin (14 points, 4/18) There have been 6 British records,
the earliest was a mere 12 years ago and only one was twitchable.
Three of the records have been on or near the south coast, so Dorset
is as likely a venue as any for this relatively sedentary hirundine.
18th Black-headed
Wagtail (14 points, 3/18) The most distinctive form in the Yellow
Wagtail group, breeding in the Balkans eastwards. It may be some time
before it is given specific status by the BOU, but many birders already
consider it 'tickable'. With only 8 British records it may seem a
bit of a long shot, but as interest in this group continues to grow,
unusual wagtails will receive ever greater scrutiny.
19th Killdeer
(13 points, 2/18) With 56 records, this American plover has occurred
in Cornwall, Devon Sussex and Hampshire (including Christchurch Harbour
in 1859). Occurrences typically occur very late in the year following
severe trans-Atlantic storms.
20th Audouin's
Gull (12 points, 2/18) The only species in the top 20 that would
also be a first for Britain (the other, Black-shouldered Kite, appears
in the 'also rans'). The population and range of this beautiful gull
has increased in leaps and bounds in recent years and vagrants have
occurred as close as northern France. Perhaps the first British Audouin's
will travel north with a group of Yellow-legged Gulls, so that Holes
Bay in late summer could be the place to search.
The remaining
29 species were:
Canvasback (9
points, 1/18), Spectacled Warbler (7 points, 3/18), Swinhoe's Storm-petrel
and Solitary Sandpiper (6 points, 1/18), Willet and Black-billed Cuckoo
(5 points, 1/18), Blackpoll Warbler (4 points, 3/18), Lesser White-fronted
Goose, Lesser Crested Tern, Sora Rail, White's Thrush and Rose-breasted
Grosbeak (4 points, 1/18), Collared Flycatcher and Baltimore Oriole
(3 points, 2/18), Greater Yellowlegs and Siberian Thrush (3 points,
1/18), Grey-cheeked Thrush (2 points, 2/18), Lesser Kestrel, Baillon's
Crake, Slender-billed Gull, Oriental Turtle-dove, Blue-cheeked Bee-eater,
and Crested Lark (2 points, 1/18), Double-crested Cormorant, Black-shouldered
Kite, Western Sandpiper, Long-toed Stint, Cliff Swallow and White-throated
Sparrow (1 points, 1/18).
The Dorset checklist
published by the Club listed 396 species up to the end of 1997. Since
then the 1998 Blyth's Pipits have been accepted and Olivaceous Warbler
has been deleted then re-admitted on the basis of the July 1999 bird.
Iberian Chiffchaff and of course, Marsh Sandpiper are pending, whilst
to the best of my knowledge there has been no documentation of the
Chimney Swift in Swanage. Thus the Dorset list has been increased
by one and regrettably seems likely to go through the magic 400 figure
through the process of splitting, rather than by a genuinely new occurrence.
Ian Lewis, April
2000.
A summary of Stour Ringing Group's research into the European
Nightjar Caprimulgus europaeus in Dorset.
During 1979 whilst
setting nets before dawn to ring Sand Martins at a colony near Wareham,
Trevor Squire found it was possible to tape lure and trap European
Nightjars (hereafter Nightjar). Members of the newly formed Stour
Ringing Group (SRG) realised that there was a locally common, yet
nationally declining, species about which little was known of its
movements or breeding biology, that could now be ringed with relative
ease. With the permission and co-operation of the Forestry Commission
(now Forest Enterprise) SRG embarked on a study of the species movements
and breeding biology that continues to this day (albeit recently at
a much lower intensity). The work was centred on Wareham Forest, but
birds were also studied in Puddletown Forest and National Nature Reserves
adjacent to Poole Harbour and a number of other sites.
From 1980 until
1983 the emphasis was on trapping adults using a tape lures (Squire
and Alexander 1981) to determine site fidelity, movements between
sites and, as always, in the hope of establishing long distance recoveries.
Nests were located by cold searching by SRG members and also during
the routine operations of the Forestry Commission. Pulli growth rates
and development were measured and correlated with weather and state
of the moon. A technique was also developed to safely net incubating
/ brooding females on the nest.
Much of the initiative
in this stage was carried out by Ian Alexander and Trevor Squire,
and in 1983 SRG became the first amateur ringing group to use radio-transmitters.
Initial attempts to track nightjars met with limited success, but
the radio-tracking program acquired greater momentum in 1985 when
Brian Cresswell joined the group. Working for Biotrack, his expertise
in the construction and fitting of miniature radio transmitters, and
the advent of smaller, more efficient circuits allowed birds to be
tracked over greater distances. Radio transmitters were either glued
to mantle feathers or tied to the retrices. Most were shed within
a few weeks; all were shed by the next moult (Alexander I. and Cresswell
B. 1990). Birds were tracked from a car, both on the network of forestry
tracks and on public highways, on a nightly basis. As it became clear
that birds were moving a considerable distance from their nest sites
Dave Eyles was employed (from grants from the Manpower Services Commission
and the World Wildlife Fund) to monitor when in the night tagged birds
returned from foraging to the nest area.
Other technological
innovations included a radio tags with a thermister that was fitted
in the axilla. The lower temperature experienced by the thermistor
whilst the bird was flying, produced a faster signal that discriminated
between perched and active birds. Tiny fluorescent 'beta lights' were
attached to the tag allowing birds to be followed using an image intensifier
and this along with the data from the thermistors identified the 'fly-catching'
and 'trawling' feeding methods. At a later stage, a data logger was
positioned close to nests to record the arrivals and departures of
tagged birds by monitoring the signal from their transmitters.
It is important
to emphasise that in spite of this 'hands on' approach there was no
evidence that the birds were harmed or handicapped in any way. Growth
rates from chicks in nest found by radio tracking were identical to
those found by routine forestry operations in areas were adults were
neither ringed nor tagged.
A lot of data
was accumulated, most of which has been published, unfortunately the
most important findings occurred a little too late to include in the
relevant volume of BWP. The main discoveries can be summarised under
the following headings:
Activity patterns
Many trapped birds
showed a pronounced 'body bulge', an accumulation of prey items in
the gizzard. Averaging the weight of birds with different sized bulges
it was possible to show that birds could collect up to 10 grams of
prey items in foraging excursions. This bulge was shown to develop
quickly in the early evening indicating that this was the peak feeding
time.
Radio tracking
also showed Nightjars to be most active at dusk and dawn and relatively
inactive during the night (Alexander I. and Cresswell B. 1990). A
'trawling' method of feeding where the bird flew around apparently
at random was identified, as was a 'fly-catching' (strictly 'moth-catching)
method, where the bird would sally out from a perch to catch a specific
prey item in the manner of a flycatcher (Cresswell B. 1996).
Fly-catching was
shown to occur more often during the middle of the night, the birds
presumably having fed by the more rewarding sustained flight after
dusk. Fly-catching occurred more often on warmer and moonlit nights,
but then only in the middle part of the night. Presumably on cooler
and darker evenings insect availability was lower and the more energetic
'trawling' method was required throughout the night. (Cresswell B.
1990)
Nightjars feeding
away from breeding areas.
Nightjars have
been difficult to study due to their nocturnal habits. It has always
been assumed that birds defend and remain close to a feeding territory.
However from the 1930s to the 1970s a number of papers in Britain
and Germany reported birds feeding away from suitable nesting habitat,
sometimes in loose aggregations around abundant food sources.
Radio tracking
of birds in Dorset showed that Nightjars do not spend all night at
their breeding sites (Alexander I. and Cresswell B. 1990). Most radio-tagged
birds left their roost at dusk and after a short bout of churring
(in the case of males), flew rapidly out of range. Birds were followed
by the researchers, initially on foot, then by car, it often taking
several evenings following the same flight path before the destination
of each bird was established. Birds were found to be feeding at sites
up to 7km from the clearings in Wareham Forest; the preferred habitat
was deciduous woodland, orchards, village gardens, ponds, streams
and water meadows. Birds were often found to be using the same area
on subsequent nights and birds that were not radio tagged were occasionally
seen in these areas, although none were ever heard to chur there.
Similar results
were obtained from bird breeding on Hartland Moor NNR with some birds
feeding over salt marsh and other atypical habitats.
The foraging excursions
were often in three distinct phases, an outward flight with occasional
pauses to feed, followed by protracted feeding at the chosen site
with a fast and direct return to the breeding site. Most Nightjars
returned from feeding by the end of the first third of the night and
often returned to the feeding area for a second time before dawn.
Aside from the
SRGs studies, evidence has been accumulating over the past decade
that Nightjars can be observed over the open sea (P. Harris per com).
On ten or more occasions birds have been observed from the Chesil
Bank at Ferrybridge flying low over the sea for protracted periods
in a manner resembling that of a storm-petrel or a Common Sandpiper.
The birds have always been seen on still evenings in mid to late May,
but this may be due to observer bias, as these are the times of day
and year when observers visit the Chesil looking for seabird passage.
The birds usually remain a kilometre or more offshore, but have flown
close enough on occasions for a positive identification to be made.
It is possible that these birds are migrants that are 'marking time'
until they can come ashore under the cover of darkness or it is possible
that there is sufficient insect life above the sea surface (presumably
blown off the land) for Nightjars to forage.
Evidence of mate-switching
and serial polyandry
From earlier studies
(Lack 1930) it was concluded that Nightjars are double brooded and
that the two nesting attempts overlap. Females would leave the first
brood when about 12 days old in the care of the male and would lay
another clutch, by the time the eggs of the second brood had hatched
the first brood had fledged and both adults could care for the second
brood.
Results of ringing
and radio-tagging have indicated that although this may be the case
for many Nightjars this is not the whole picture. Cases of serial
polyandry and mate switching were noted. For example one radio-tagged
female left her first brood to the sole care of her mate - who was
also radio-tagged - at about the predicted time. However instead of
starting a new nest nearby she started one in another clearing 400m
away. When she left her new eggs one evening to feed it was found
that they were incubated by another unmarked male. She was never seen
again near her first brood and her first mate was never near her second
nest. She had switched mates.
Although this was the only instance when a female switching mates
was recorded, there were only a few cases where it was known for certain
that a pair had stayed together. It was unusual to find both birds
of a pair radio-tagged throughout the summer, and without tags it
was not possible to identify them at a distance or to recognise birds
at a nest site (unless ringed birds were trapped there). It is all
too easy to assume that a bird seen repeatedly at a particular site
is always the same bird. There is often a presumption that bird pairs
show a high level of fidelity, but DNA analysis and studies of marked
birds in a variety of species show that this is not always the case.
Lunar synchronisation of breeding
Another interesting
aspect of Nightjar breeding behaviour is their apparent synchronisation
with the moon (Cresswell B. 1992). Nightjars seem to prefer to start
their nests at the time of the full moon. However, they do so only
if the full moon coincides more or less with the period when they
would start nesting anyway. For instance if a full moon occurs in
the first half of June, most nests will be started within a day or
two of it, and there will be relatively few nest start-ups in the
week before and the week after. On the other hand, if the full moon
is near the end of May, just before most Nightjars are ready to start
breeding, nest start-ups will be spread more evenly throughout the
first two weeks of June.
It is difficult
to imagine how Nightjars could benefit at the time they start to synchronise
with the lunar cycle. It is likely that the benefits come later instead.
The fledging date of young in a nest that was started on a full moon
in early June would coincide with the next full moon in early July.
It is thought that it is at this time of the 'second' full moon that
the Nightjars benefit from their lunar synchronisation. The extra
light provided by the large moon may enable more efficient foraging,
so that adults can satisfy the peak in food demand of their offspring,
and the fledglings will have optimum conditions in which to learn
to forage for themselves.
As well as being
synchronised with moon phase, Nightjar nesting behaviour is also affected
by the weather. In particular cold weather in the period following
the arrival of females from their winter quarters appears to cause
them to delay the date of egg laying (Berry and Bibby 1981).
Nest and roost
sites
The bare earth
'scrape' that serves as a nest site for this species is usually located
in open areas such as heathland or forestry clearings. However 15%
of nests located by radio-tracking of the adults were located in medium-height
plantations more than 5m high. Nightjars normally lay two eggs but
occasionally there is only one. A nest found by SRG with four eggs
comprised of two distinctly marked pairs were almost certainly from
two females.
Mature plantations
rather than clearings, were the preferred roosting sites in 77% of,
mainly male, birds (females usually roosted at the nest site). Nearly
40% roosted more than 10m above the ground. Other roost sites included
fallen branches and stumps, with only 20% of males roosting on the
ground.
These results
are contrary to accepted wisdom and illustrate the problem of observer
bias. Unless a bird can be detected by a method such as radio-tracking
then it will be only found in area where the observer chooses to search
for it or are most likely to find it
Site fidelity
Analysis of data
from birds retrapped in subsequent years revealed that adults remain
site faithful. Of 81 adult birds retrapped, the mean distance moved
between years was 0.4km compared to the mean of 4.4km recorded from
44 birds ringed as juveniles and retrapped in subsequent years. This
data was significant for both sexes. (Cresswell B. 2002) This is not
surprising, as adults will presumably return to a location where they
previously bred, whilst juveniles, returning the following year, will
need to find a vacant territory.
Long distance recoveries and causes of mortality.
SRG have ringed
a total of 979 Nightjars of which 28 (2.86%) were subsequently recovered.
Nationwide 84% of Nightjar recoveries are through human related activities
such as collisions with cars, so due to this extreme finding bias,
little can be concluded about causes of mortality. Many of these recoveries
occurred close to breeding areas and hence shed little light on the
bird's migration. Similarly the occurrence of controls (retrapping
by ringers other than those who originally ringed the birds) is highly
influenced by the location of specialist ringing groups. Even so,
British ringed Nightjars have been recovered in France (8), Netherlands
(1), Spain (1) and Morocco (2) indicating a migration in a due south
direction.
Conservation
It is clear that
the discovery that Nightjars travel considerable distance from their
nest sites to feed has considerable conservation implications, as
recognised by the fact that the species has its own Biodiversity Action
Plan. The decline of the Nightjar from the 1930s to the 1980s (Morris
et al) may have as much to do with the loss of old orchards, hedgerows
and watermeadows as it does to the loss of heathland. Increase use
of pesticides may have had an affect of Nightjar numbers, analogous
to that seen in many populations of bats. On the other hand the large
areas of forestry land cleared by felling in has created large areas
suitable for nesting. This however reached its peak the 1980s and
many replanted areas are now no longer suitable, as Nightjars seldom
nest in conifer plantation when they are more than 10 - 20 years old
(Morris et al). In Dorset large areas of former plantation are in
the process of being converted back to heathland, however the work
carried out by SRG shows that both breeding and feeding areas must
be conserved.
Further work
Recent work has
demonstrated that individual churring males may be recognisable through
sonogram analysis, using a dedicated program that analyses both pulse
rates and phrase lengths (Rebbeck, et al 2001). This has major implications
for the estimation of population size and adult survival, however
cannot be used to determine how far an individual bird forages, as
they are invariably silent when away from the nest area.
Acknowledgments
I wish to thank
Brian Cresswell for his constructive comments on earlier versions
of this article.
References
Alexander I. and
Cresswell B. 1990 Foraging of Nightjars Caprimulgus europaeus away
from their nesting areas. Ibis 132 (4): 568 -574
Berry R. and Bibby C. 1981 A breeding study of Nightjars. British
Birds 74: 161-169
Cresswell B. 1990. The effects of moonlight and temperature on Nightjar
foraging. Stour Ringing Group Annual Report 1989
Cresswell B. 1992 Nightjars and the moon. Stour Ringing Group Annual
Report 1991: 36 - 37.
Cresswell B 1996 Nightjars - some aspects of their behaviour and conservation.
British Wildlife vol 7 no 5 297 - 304
Cresswell B. 2002 in Wernham et al 'The Migration Atlas - Movements
of the Birds of Britain and Ireland' T&A.D. Poyser
Lack D.L. 1930 Double-brooding of the Nightjar British Birds 23: 242
- 244
Morris A. Burgess D, Fuller R.J., Evans A.D. and Smith K.W. The Status
and distribution of Nightjars Caprimulgus europaeus in Britain in
1992. Bird Study (1994) 41, 181 - 191.
Rebbeck, M., Corrick, R., Eaglestone, B. & Stainton, C. (2001)
Recognition of individual European nightjars Caprimulgus europaeus
from their song. Ibis, 143, 468-475.
Squire T. and Alexander I. 1981 Capture techniques for full grown
Nightjars. Ringers Bull. 5: 132.
Ian Lewis 28/7/03
