There must be something about Nick and me that doesn’t inspire confidence. I admit that my son’s careers officer once likened me to small-scale wheeler-dealer Del Boy, and Nick did at one time sell classic cars for a living. As long ago as 2006, we nagged the BTO and anyone else that would listen that the WeBS numbers weren’t up to scratch. We met Andy Musgrove, the BTO’s head of monitoring, even bought him lunch at The Blue Boar. An extraordinary general meeting was held with all the counters present, but after careful consideration it was decided that nothing needed to change.
So Nick and I decided to run our own survey alongside the WeBS counts. We recruited professional bird surveyors Neil Gartshore and Dave Chown to count alongside Nick. Nick worked out the optimum state of the tide for each part of the harbour. He used Dave Collins’ survey from 22 years ago as his template. During the same time, Neil was also working on a Nature Conservancy study, surveying wader habits after dark. So he was purposely sent out at night, but unlike the WeBS counters he was issued with night vision optics.
The single biggest discovery we made was that one person counting the birds on Brownsea lagoon at high tide gave a better idea of peak numbers than the maximum winter WeBS counts for the whole harbour. WeBS counts at low tide gave a maximum of 2,350 Dunlin, while our survey saw 3,001 in one count on Brownsea lagoon. It was the same for three other species: Red Knot – WeBS 43, Brownsea lagoon 143; Grey Plover – WeBS 53, Brownsea lagoon 235; and Ringed Plover WeBS – 43, Brownsea lagoon 74.
Under the guidelines for WeBS observers, gull counts are optional. Our own co-ordinated count of 4,500 Herring Gulls reached the threshold for national importance, while the highest WeBS count for the same period (896) did not. We also used surveyors who could identify Yellow-legged Gulls in all plumages, finding 170 at two sites, while the highest WeBS count was 19 birds in 2008/09.
Meanwhile, the Nature Conservancy’s night study compared bird numbers during night and day on the northern shores. It highlighted a few species, like Ringed Plover, Grey Plover, Dunlin and Common Snipe, of which more fed at night than during the day. Most excitingly, four Jack Snipe that we never see feeding during the day were spotted in Holes Bay at night.
Strangely, Studland Bay (just outside the harbour proper) has never been included in the local WeBS counts. It’s great for Black-necked and Slavonian Grebes, although they also get into Brand’s Bay off Arne, and between the islands.
Studland Bay has 250 acres of eelgrass, and in 2004 it was found to hold a population of 40 adult Spiny Seahorses Hippocampus guttulatus. The government is to set up a network of 43 Marine Conservation Zones, and was considering Studland Bay as one of the 13 of these sites that shouldn’t be disturbed at all. The Daily Telegraph wrote an article about the fuss it has caused (Sailors vs seahorses: the battle of Studland Bay, Saturday 19 November 2011). It describes a battle between the local boat owners who have been mooring boats here since time immemorial and the marine conservationists who believe this damages the eelgrass meadows and therefore the breeding conditions for the sea horses. The locals think the eelgrass has expanded over the past years and that they should be able to continue, while the conservationists argue that the density of sea horses is low considering the habitat and that there should be at least 200 adults. In the end, the designation has been delayed due to a lack of data.
Could Black-necked Grebes actually be part of the problem? Pipefish, which are closely related to seahorses, are known to be among their prey. Fully grown Spiny Seahorses are approximately 17 to 18 cm from the top of the coronet to the end of the tail, so presumably too big. Although they breed more frequently from the spring, they can breed throughout the year, so perhaps their ‘seafoals’ might form part of the grebes’ winter diet.
Over the past five years, Black-necked Grebe numbers have been rising spectacularly at Studland. In 2011, Stephen Morrison started to watch the evening roost off Studland beach and counted 80 birds. That is the largest flock in Britain, where a flock of five is nationally significant. It is also four times the size of the other significant flocks at Langstone harbour in Hampshire and the Carrick roads in Cornwall. Stephen takes great care to get the numbers right.
“Watching the grebes come in to roost in the evening, I often pick up a number of birds coming in from the north-east and east from beyond the Training Bank and I can only think that during the day they have just been beyond the detection range for me even in calm conditions. With large numbers, and despite the greatest of care and skill, it is not too difficult to overlook those birds that insist on staying under the water for longer than they should. (I remember once having to wait 20 minutes to determine that there were actually 5 birds in a small flock, and not 4, when watching off Pilot’s Point.)”
When Durwyn Liley did a study of the disturbance to the grebes in Studland Bay in 2005/06, he noticed that many of the grebes didn’t fly between the spots but swam. As adult Black-necked Grebes are virtually flightless for most of their stay with us, it’s likely that any Black-necked Grebe you might see flying will be a first-winter bird. Strong easterlies upset the grebes’ and the seahorses’ habits, and it is then that the grebes all move to feed off the south shore of Brownsea.
As for Slavonian Grebes, according to ringing recoveries, ‘ours’ are from Finland, Sweden or Norway. They hang about off the shore of Bramble Bush Bay or off Arne more often than Black-necked Grebes. There used to be 22 on average, but now numbers are much lower, with only three or four in recent years. Sadly, we have no idea why, and the WeBS counts have missed most of them.
Some species are considered too secretive to be counted as part of WeBS. Water Rails for example. If you look in British Birds journal’s rare breeding birds report for 2008 (Holling & the Rare Breeding Birds Panel 2010), you will see that it only received reports of six territories of Water Rails in Dorset. Various other reports over the years suggested between 13 and 30. In 2004, Dave Chown squelched through our reed beds on a specially designed survey, playing taped Water Rail calls and counting responses. He surveyed 13 of Poole’s reedbeds on seven mornings between 27 March and 20 April.
Dave found 211 pairs of Water Rail and 63 ‘single’ birds, and he still thought this was a minimum. The ‘single’ birds could have included breeders, and because surveying had to go on into the day when Water Rails are less responsive, Dave thought some pairs must have been overlooked. So in a godlike seven days, Dave increased Britain’s total of Water Rail territories by 21%.
Why does Poole have so many? Once the young Water Rails have fledged they are not thought to travel far, and if we take the pessimistic view that half the pairs successfully rear four young, that would take the population to 750. Large numbers of migrant German, Danish and Slovakian Water Rails are known to arrive here to winter. If you add that to our resident families, it wouldn’t be unreasonable to have 1,500 individuals here in January. I should add that although these numbers add significantly to Britain’s Water Rail population, Dave suggests that it isn’t only Poole that doesn’t know how many Water Rails it hosts.
Through his survey, Dave also gained some interesting insights into the harbour’s ecology. “Water Rails were particularly numerous in areas where deer tracks were frequent (for example, the whole of the East Holton and Holton Heath).” He noticed that the Water Rails appeared to use the tracks to move around their territories. “By increasing the extent of standing water and bare mud in reed beds, deer tracks probably provide improved foraging conditions for the rails” (Chown 2004). And there is more to this web of ecological relationships than just deer and rails. The grass itself is Spartina, accidently introduced from North America, and native Redshanks are suffering because of its decline.
Japanese Sika Deer were first introduced to Brownsea Island in 1896. Being able swimmers, they started to leave the island, deserting it completely in 1934 during the big fire. As you may remember, by this time Spartina had arrived, hybridised and quickly colonised a third of the harbour, creating the most dramatic change in 400 years. Sika Deer have sturdy digestive systems and like to eat the Spartina. Now we had alien deer taking advantage of an alien grass.
The fact that both are aliens is important, because as a rule conservationists are purists and try to control non-indigenous flora and fauna. Sika don’t only eat the Spartina, they also eat crops, damage trees and become a nuisance in gardens and nature reserves. On the other hand, they trample the edges of the salt grass, allowing indigenous grasses to return. The tenant farmers hate them, especially those where their landowners lease out the deer shooting. They find themselves growing crops for the Sika Deer to give a bit of sport to the shooters, who pay the farmers’ landlords for the privilege of selling the ‘venison’.
A rough estimate puts Purbeck and Poole Sika numbers at 5-7,000, one of the highest densities in Britain. Between foresters, conservationists, the army and landowners, I’m told that 1,000 a year have been culled over the past few years. The intention is to carry on shooting them, “until they are no longer a nuisance”. I don’t like shooting, but suspending my natural wish to put all the perpetrators on my little list, it’s interesting to explore this decision to ‘cull’ Sika Deer a little more scientifically.
It is thought that in the absence of predators, Sika populations increase roughly 10% a year. If 1,000 a year are being killed (between 14% and 20%), this will bring down the numbers (May & Humphreys 2005). In Japan, however, they calculate that the unpredated annual increase rate of Sika deer is far higher at 16-21% (Matsuda et al 2002). If the Japanese figures are right, the current rate of shooting will have no effect on the deer, which could be good news for Water Rails but perhaps bad news for Redshanks.
As far as we can work out, Redshanks really flourished from 1900 when the Spartina started to cover the mud flats and provided more nesting opportunities. Breeding numbers in the early 20th century were suspected of reaching 100 pairs several times, but dropped to just six pairs after the cold winters of the early ‘60s. Because of this, we realised that the Redshanks breeding in the harbour were sedentary. By the middle of the ‘80s, numbers had recovered and we had some of the highest breeding densities in Britain, rising to 103 pairs by 1994 (1% of Britain’s breeding population). But by 2002, Redshank breeding numbers had dropped again.
As we saw, the amount of mud flat covered in Spartina halved between 1924 and 2004. So we have more Sika feeding in half the area, and only half the space for the Redshanks’ nests. Meanwhile, as other nature reserves like Sunnyside farm and The Moors become wetter, some Redshanks are returning to breed in their more natural habitats.
A 2004 study showed that breeding Redshank numbers in Poole Harbour were down to 69 pairs, a reduction of 19% in the eight years since 1997 (Cook 2004). There was a strange disparity between the north (Keysworth and Holes Bay), where numbers had halved, and the south (from Brand’s Bay to Swineham), where the population had increased by five pairs to 51 pairs.
One of the reasons suggested for the Redshanks’ decline was that the deer tracks made it easier for predators – perhaps Red Foxes, or Brown Rats – to find the nests and eat the young. But the deer are just as prevalent all around the harbour and you are more likely to see a fox at Middlebere than in Holes Bay. Interestingly, areas that had the highest Water Rail counts had the biggest declines in Redshank breeding numbers. Water Rails are carnivorous, and perhaps young Redshank are tasty.
While all these surveys are very interesting, none so far have told us whether or not WeBS should be counted at high tide. Although the lagoon high tide roosts were producing higher numbers, we now know that the WeBS were being dramatically under-counted. Seeing the figures at the conference inspired Shaun, Nick and me to organise a ‘Big winter bird count’ (BWBC). Based on the Western Hemisphere ‘Christmas bird count’, we invited local birders to give up any part of their day on 8 January 2011 to count any and all the birds in the harbour area. The idea was simply to provide a snap shot that might illustrate where future counts needed to be made. Having by now concluded his studies of Poole’s birds, Nick had a good idea of where everyone should go and when. 46 birders took on the challenge to record as many species in the Poole Harbour area as was collectively possible – with targeted searches for Great Grey Shrike, which was found, and Lesser Spotted Woodpecker, which was not. In addition, we were to do a high tide count of all wildfowl and waders, and roost counts of grebes, Goldeneyes and Starlings.
Common Shelduck Tadorna tadorna, Brownsea lagoon, Dorset, 13 September 2011 (Nick Hopper). ‘Numbers at Poole of national importance.’
It turned out to be a wonderful day. Collectively, we found 143 different species and counted a minimum of 114,269 birds. Now admittedly 62,000 of those were Starlings, but considering Poole town has a human population of 138,000, it was still a fair few.
Among a series of interesting records, Peter Hadrill had six Marsh Harriers coming out of their roosts in the Wareham Channel, and 31 Woodcocks were found by all the counters, which is nationally significant. There were nine Firecrests scattered through the harbour, a record 410 Gadwall, 121 Magpies roosting at Hatch Pond, 10 Golden Pheasants, 18 Sparrowhawks, four Peregrines, two male Hen Harriers and a couple of Merlins.
Our various surveys enabled us to reach several conclusions. First, since Dave Collins’ 1984 survey, the lagoon had become the most important roost site in the harbour. Second, that the important bird populations had not dropped out of national significance: they just weren’t being counted properly. Third, our counters still found it hard to see waders at high tide. Redshank numbers for example were half what we knew them to be at low tide.
We reckon that just on the BWBC, Avocet numbers at 1,249 were above their international threshold which is 730, while there were 1,270 Black-tailed Godwits (international threshold 470). 1,741 Shelduck however were only nationally important (international threshold is 3,000). And the birds that had concerned Kevin – Dark-bellied Brent Goose, Common Teal, Pintail and Black-necked Grebe – were all found in nationally important numbers. With nationally significant numbers of Great Cormorant, Water Rail, Greenshank, Herring Gull, Yellow-legged Gull and Mediterranean Gull, and most importantly a total of wildfowl, waders and gulls using the harbour in winter nearer 30,000 than 20,000, Poole Harbour’s status as an internationally important assemblage of waterfowl seems assured.
As for the issues with WeBS in Poole, it seems that while computerising the processing of data, the BTO organisers hadn’t maintained their high standards of data gathering. Now, however, we have all got our act together. The RSPB are providing an organiser (Paul Morton) with backing from the Dorset Bird Club. Birders have been recruited to count all the areas, using knowledge gained from our own 2007/08 survey and the BWBC.
Stragglers Shaun, Nick, Mo and I will be attempting to rejoin the wheeling flock of counters next time on Sunday at 15:00.