Arctic Terns have the longest migration in the animal kingdom, and you will know that, because they spend the breeding season in the northern summer and the non-breeding season in the southern summer, they see more daylight than any other animal. You will also probably have read that during their life times they can travel up to the equivalent distance to a round trip to the moon and back - three times.
Remarkable as all that is recent studies have shown that we have seriously underestimated just how far they do travel. In 2011 five Arctic Terns breeding in Holland were fitted with geolocators, and these were recovered the following summer (Ref 1). The journey they took was remarkable as shown on the map.
Annual migration route of Dutch Arctic Terns as discovered by geolocators (Fijn et al/Ardea).
After leaving Holland in late July they
flew west to a staging area out in the northern mid-Atlantic where they
joined birds from Greenland and Iceland, this mid-Ocean staging area
was only discovered in 2007 during similar studies of Greenland and
Icelandic breeding Arctic Terns also fitted with geolocators. They then
flew south past the west coast of Africa before pausing off Namibia
flying round the tip of South Africa before reaching a previously
unknown staging area in the middle of the Indian Ocean. They then flew
south-east to spend the winter on the Antarctica coast south of
Australia, with one bird getting as far as New Zealand. So they flew
to Wilkes Land which is on the
far side of Antarctica from the south Atlantic! Total
flying distance from leaving Holland in the summer of 2011 and
returning the following spring was around 56,000 miles, compare
this with the circumference of the Earth which is 25,000 miles. Just
I've rather extravagantly
called the square which has New Brighton in the southern
corner, the Isle of Man in the north, north Anglesey to the west and
Foulney Island to the east - 'Greater' Liverpool Bay. In that square we
have more Arctic Terns breeding then Common Terns and these
include the largest breeding colony of Arctic Terns in the
United Kingdom just 56 miles from Hilbre. This is on the
Skerries just off the north coast of Anglesey, the colony here has been
increasing steadily since the 1980's and reached an astounding 4,234
pairs in 2014. Pretty remarkable when you consider that the
large majority of Arctic Terns breed in the Northern Isles and
north-west of Scotland where numbers have been decreasing.
We also have several smaller colonies in this area, and these include (note numbers of breeding pairs can vary greatly from year to year): Cemlyn Bay with 40 pairs, Ribble marshes with unknown numbers breeding but some years could be at least 10 pairs, Isle of Man with 30 pairs, Foulney Island with 30 pairs.
It is unlikely that we see any of these birds here on the Dee estuary/North Wirral during the actual breeding season although immatures and failed breeders associated with the colonies may well wander along our coast. However, some of the birds we see before and after breeding may come from these colonies and this is discussed further below. But first, identification......
It says in my New Naturalist book 'Terns' that Arctic Terns are "very easy to distinguish" from Common Terns. I have to admit it is an art that I have yet to master but that is because I'm lazy and I'm sure once you have learnt the differences between the species and given a bit of experience in the field then the authors of Terns are quite right. But they are talking about birds reasonably close to, especially those on the ground. A recent article in British Birds (Ref 6) points out that identification is much more difficult when the birds are flying at some distance and the author comments that flocks of terns seemed to be routinely identified as different species as they fly up the Severn Estuary, with one group of birders identifying them as Arctic and the next group identifying the same flock as Common, with the latter almost always correct.
Up until the late 1980s most birders didn't even attempt to differentiate between Arctic and Common Terns, calling them all 'Commic' Terns. Since then, as my 'Terns' book points out, it is now well documented that the two species do differ in many subtle ways. It has, perhaps, now gone too far the other way with birders over confident when trying to differentiate Arctic and Common Terns and not willing to call them 'Commic' as that would be an admission of failure. Nevertheless, any experienced birder having good and reasonably close views should have no trouble telling the two species apart.
Anyway, the point of all this is that the correct identification of Arctic Terns does appear to be an issue here in the Dee Estuary and North Wirral with the majority of reports in July and August greeted with scepticism by some. Recent Lancashire Bird Reports suggest similar problems with birds off Formby Point during July and August with the following being a typical quote (2012 Bird Report) - 'One group of experienced observers reported sightings from Formby Point on seven dates...including 55 on July 18th, while another regular sea-watcher at nearby Cabin Hill reported just one sub-adult on July 9th'.
Nevertheless, as the next section shows, there is no reason why we shouldn't be seeing Arctic Terns here on the Dee estuary in late July and August so we have to take reports at face value whilst still being aware of the identification difficulties.
For those, like me, who are not sure how to tell them apart then there are many sources on the internet to help you with the BTO Video on this subject (click here) one of the best.
Just to the north of us a major spring passage of Arctic Terns is monitored every year by Heysham Bird Observatory and three-figure daily totals from mid-April into May are commonplace there. Max counts are usually around the 400 to 500 mark but 2011, to quote the Lancashire Bird Report, was 'phenomenal' with a total of 14,157 birds counted and the max count an amazing 8,153 on May 3rd. Sight observations strongly suggest that these birds gain height in the evening before heading north-east, so presumably crossing the country to the North Sea over-night; it therefore seems likely that these birds are part of the very large population breeding in Scandinavia and Baltic States.
birds we get here on the Dee estuary in spring are probably part of
this same movement but
much smaller numbers are involved with a total of just 12
counts in April and May for the years 2005 to 2013. The first graph
below shows the totals for those years in 10 day periods during April
October for the Dee Estuary and North Wirral. The second graph is for
Dungeness over a similar time period, Dungeness is located at the
narrowest point of the English Channel and is a prime site for studying
the migration of Arctic Terns and it is interesting to compare the two.
Both the spring and autumn peaks occur in the same period at both sites, in the last third of April and the last third of September respectively - and these birds may well be the ones flying to and from colonies in Scotland, Scandinavia and other parts of northern Europe. For the return migration at Dungeness numbers start to pick up through August before increasing further in September. On the Dee estuary we also get a few birds in August (remember the graph is showing totals over a nine year period so only very small numbers are involved at any one time), they can be hard to find with many recorded off Hilbre and the far edge of East Hoyle Bank rather than the main roost site at Hoylake.
Fijn et al., in their article about Arctic Terns fitted with geolocators, describe how the birds left the Dutch colony in the first week of July but then stayed in the North Sea region in relative close proximity to the colony, before moving on at the end of July. If birds in the 'Greater Liverpool Bay' colonies are doing the same thing this would neatly explain why we see a summer peak of numbers in the second half of July whilst birds are staying in the general area for a couple of weeks - remember over 4,000 pairs are breeding just 56 miles from the Dee estuary. This is in contrast to Dungeness where the nearest colonies are several hundred miles to the north and consequently counts in July are very low. Fijn et al. also found that two of the five birds which they were tracking left the North Sea by crossing the UK into the Irish Sea, proof that birds from colonies to the east of us do find their way into the Irish sea in summer and therefore could be observed from our shores. Other indications that many Arctic Terns in the Irish Sea post-breeding originate from the North Sea and the Baltic States come from ring recoveries at Dublin Bay; here they see Arctic Terns regularly staging with Common Terns in August, usually in quite small numbers but occasionally in their thousands.
we would be amazed at the number of Arctic Terns that actually pass
through the Irish Sea on migration if only we could track them all -
unfortunately most are way out to sea, fly over at great height or
migrate at night. But we are lucky enough to see a few here on
Dee estuary every year; most of the time they are vastly
outnumbered by Common Terns and easily confused with them by the
unwary. But when you do get a good view and are certain of the
identification it is an awe inspiring sight knowing the immense
distances they travel.
1. Fijn R.C., Hiemstra D., Phillips R.A. & van der Winden J. 2013. Arctic Terns Sterna paradisaea from The Netherlands migrate record distances across three oceans to Wilkes Land, East Antarctica. Ardea 101: 3–12
2. Egevang C., Stenhouse I.J., Phillips R.A., Petersen A., Fox J.W. &Silk J.R.D. 2010. Tracking of Arctic terns Sterna paradisaea reveals longest animal migration. PNAS 107: 2078–2081.
4. Welsh Onithological Society,
National Conference 2012:
6. Keith Vinicombe, The migration of Common and Arctic Terns in southern England, British Birds 107. April 2014 (data for Dungeness graph taken from this article, original data courtesy of Dungeness Bird Observatory - http://www.dungenessbirdobservatory.org.uk/).7. DEFA's Biodiversity News, July 2014.
8. Swn y Mor, Anglesey AONB Newsletter, Issue 16, 2015.
9. Roger Lovegrove, Graham Williams and Iolo Williams, Birds in Wales, Poyser, 2010.
10. Lancashire Bird Reports 2001 to 2013.
11. Cheshire and Wirral Bird Reports 2001 to 2013, CAWOS.Richard Smith
Spanish ringed Black-tailed Godwits, or even ones recorded in Spain, are quite rare here on the Dee estuary but we have seen three over the past few weeks on their way to Iceland, these include 'Tirns', which featured in the June Newsletter, with details of the other two shown below along with one of our more regular birds.
As mentioned elsewhere in this newsletter there was a late passage of small waders with unusually high numbers of Sanderling in early June - it is very likely that all these Sanderlings will have over-wintered in Mauritania, west Africa, and the two ringed ones we saw both came from there.
June is always a quiet month and this year was no exception, but there was still plenty of interest. Rarities included a Caspian Gull at Hoylake on the 1st and a female Red-necked Phalarope at Burton Mere Wetlands on the 2nd and 3rd, then surprisingly it, or another, was present on the 15th. The 26th brought a Serin to Meols and a Ring-billed Gull to Burton Mere Wetlands.Dark-bellied Brent Geese are certainly a rarity in June and what one was doing at Burton Mere Wetlands on June 28th I'm not sure, a male Pochard there was also unexpected and was initially mistaken for something much rarer! A flock of 10 Eiders, nine of which were drakes, were off Hilbre on the 4th.
3rd July, 12.47hrs (BST), 9.2m.
4th July, 13.31hrs (BST), 9.3m.
5th July, 14.17hrs (BST), 9.3m.
Organised by the Wirral
Ranger Service , Flintshire
Countryside Service and the
RSPB (Dee Estuary):
All these events and walks have bird interest, even those not advertised specifically for birdwatching. No need to book for these events unless specified - please check below.
Also see 2015 Events Diary.