The cliffs along Marine Drive, Scarborough, are bare and strangely quiet now that winter is coming. The kittiwakes have long since left and are far away, over the ocean. Only a pair of lonely peregrine falcons keep watch on the cliffs now, waiting patiently for their sandeel-packed lunches to return in the new year!

According to a report prepared for Scarborough Borough Council, the kittiwakes first began nesting on Castle Headland in 1940; by 1959 the colony had increased to about 360 pairs and currently exceeds 1,500 pairs. This is in line with increases of about 3% per year in kittiwake populations – and the formation of many new colonies  – for much of the 20th Century (2). It is reassuring to learn that the kittiwake population in Scarborough is reportedly stable, unlike some other areas in the UK (see below).

At the end of the breeding season, the Black-legged kittiwakes (Rissa tridactyla) – to give them their full scientific name – leave their nesting sites and disperse widely, spending most of the winter in northern oceans ‘far from land and most humans’ according to John C. Coulson (2011) in a book called The Kittiwake (2). Until recently, our knowledge of where kittiwakes went during the winter was somewhat limited. Direct observations from ships revealed that they spread out across the whole North Atlantic during winter, reaching as far south as 30-35 degrees north (7). Once in the Atlantic ocean, they appear to be ‘nomadic’, in that their movements and locations are strongly influenced by weather conditions (7). Kittiwake movements along the coasts of Britain and Ireland in winter, have shown that they move away from Atlantic depressions and strong winds, flying perhaps as far as 1,000 km in a single day (2). According to Coulson, these ‘movements make their oceanic distribution fluid and variable’ (2). What clever birds they are!

Recently, technological advances in miniaturization have enabled researchers to attach geolocation devices to smaller birds such as kittiwakes, so that they can now be tracked through the winter. A total of 80 breeding kittiwakes were fitted with tiny (1.5 g) geolocation loggers – which amount to about 0.4% of the body weight – to a leg ring (1).  During the period between leaving the vicinity of the colony in late summer and returning the following spring, the birds dispersed to both sides of the Atlantic Ocean, as well as the North Sea. The routes taken by some birds are shown in the following diagram (Figure. 2 from Bogdanova et al., 2011). It’s amazing to think that the birds I watched nesting on a ledge above the entrance to a shop in Scarborough this summer, will be making similar such epic journeys this winter! What intrepid globetrotters they are.

Black-legged Kittiwakes usually lay two eggs (with one to three also occurring) in the Spring, around May (late April to early June)(2). After hatching, one parent always remains on the nest to brood the chick, whilst the other one goes off to look for food.

The chicks are not left by themselves until they have grown to a good size, perhaps after 33-40 days (2). The parents leave their nests for about 2 hours and 48 minutes on average, which Coulson calculates gives them a potential feeding range of 63 km (40 miles) if they fly at 45 km per hour (2). Although, they are going to need time to feed, and perhaps ever take a rest!

Another study, of kittiwakes breeding on the on the Isle of May in Scotland, found that during the breeding season the adults forage up to about 73 ± 9 km from the colony (3). During these trips the birds are looking for and feeding on a small pelagic fish: predominantly the lesser sandeel (Ammodytes marinus). Their remarkable tongue, must be an adaptation for feeding and catching such prey items on the surface of the sea.

In Scarborough, North Yorkshire, kittiwakes nest on suitable ledges all over the town, especially on old or abandoned buildings. Apparently, they only started doing this in 1994. They make quite a mess and some owners erect nets to prevent the birds from returning the following season. When this happens, and the birds arrive and cannot access their former nesting ledges, they stand around for a few weeks, before moving onto other suitable ledges or cliffs (8). I can imagine them silently muttering to themselves, who blocked off our nesting site! I shall have to watch what happens when the birds that used to nest over the entrance to M&S this year (2015), return next year and find their site covered by mesh! The birds nesting in town generally do not seem to be much bothered by the presence of people on the roads and pavements below them. I think most people like to see these birds, although some do not realise that they are very different from Herring gulls. They are all just grouped together as seagulls. Personally, I love the cry of the kittiwake!

Once the young kittiwakes have fledged and left the parental colony, they no longer receive any parental care. They only receive food from their parents at the nest site. The chicks spend about ten days around the colony after they have made their first flight (2). One morning in late July, I noticed many fledglings sitting on the breakwater on Marine Drive (below the breeding cliffs) or sitting on the water. At this stage they could presumably still return to their breeding ledge to receive a free meal from one of their parents.

It is remarkable to think that these young birds will soon be flying off, by themselves, for thousands of miles; many going as far as the other side of the Atlantic (wintering off Newfoundland and Greenland) (7). Once they leave the colony, the bond with their parents is abruptly broken, and they have to forage for themselves (2). Many of them will not return ‘home’ for a few years, and even then they will not begin to breed themselves, until they are at least three years old, possibly not until they are six (2, 7).

So once they are ready to go, it is important that they find good feeding sites. Some fly as far as 4,000 km in six weeks after leaving, probably travelling with other more experienced birds and learning from them (2). After all, it cannot all be innate! Some kittiwakes have lived for over 28 years (2) and these individuals must have accumulated a great deal of experience (wisdom) during their journeys back and forth across the Atlantic. Where to find food at sea; how to avoid dangerous storms; and so on. The younger birds can learn from their elders!

In the North Sea, kittiwakes feed on planktonic crustacea in the early spring, then switch to larger sandeels in April and May, and later on, switch to feeding on the shoals of small, newly hatched, larval sandeels, which occur near the surface in June and July (6).  There have however, been declines in kittiwake populations, perhaps in association with sandeel fisheries, as well as with increases in late winter sea surface temperature (4, 5). According to Coulson, it is not clear ‘whether these fluctuations in sandeel abundance are natural or caused by intensive fishing’ (2). But many people would agree that it would be a sensible precaution to maintain a ban on sandeel fishing to protect kittiwakes.

Coulson also downplays the effects of climate change, writing: ‘it is difficult (for me) to believe that these [changes in average sea surface temperatures of about 1 deg C in the past 30 years] have already appreciably influenced the kittiwake throughout its whole range’ (2). That may be the case, since the kittiwake has such a broad distribution, but locally there have been steep declines: for example an 87% decline in kittiwakes on Orkney and Shetland since 2000, according to the RSPB (9). The RSPB are unequivocal in putting the blame on climate change for these massive declines in Scotland’s seabird populations (9). If this is the case, there is probably not much we can at this stage, to reverse the predicted rise in ocean temperatures – perhaps as much as 2-3 deg C – in the near future. So the kittiwakes are going to have to try to adapt, as best they can, to this uncertain future. The kittiwake does have an extremely large range – in both the North Pacific and the North Atlantic – and a very large global population, estimated to be between 17-18 million pairs, according to BirdLife International (10). According to this website, the decline in the global kittiwake population is not believed to be sufficiently rapid to approach the threshold for being classed as Vulnerable (i.e. a >30% decline over ten years or three generations). It is to be hoped that if climate change does impact the food availability for kittiwakes in some areas, there are enough colonies in areas where there are alternative prey species which may be available to them. We can only hope so, and it makes one realise how lucky we are to have this beautiful bird nesting on our doorstep, and sometimes literally on our windowsills (!), here in Scarborough. Long may it prosper.

References

1. Bogdanova, Maria I., et al. “Seasonal interactions in the black-legged kittiwake, Rissa tridactyla: links between breeding performance and winter distribution.”Proceedings of the Royal Society of London B: Biological Sciences (2011): rspb20102601.
2. Coulson, John. The kittiwake. A&C Black, 2011.
3. Daunt, Francis, et al. “Foraging strategies of the black-legged kittiwake Rissa tridactyla at a North Sea colony: evidence for a maximum foraging range.”Marine Ecology Progress Series 245 (2002): 239-247.
4. Frederiksen, Morten, et al. “The role of industrial fisheries and oceanographic change in the decline of North Sea black‐legged kittiwakes.” Journal of Applied Ecology 41.6 (2004): 1129-1139.
5. Frederiksen, Morten, et al. “Regional and annual variation in black-legged kittiwake breeding productivity is related to sea surface temperature.” MARINE ECOLOGY-PROGRESS SERIES- 350 (2007): 137.
6. Lewis, Sue, et al. “Diet and breeding performance of black-legged kittiwakes Rissa tridactyla at a North Sea colony.” Marine Ecology Progress Series 221 (2001): 277-284.
7. Wernham, C. V., et al. “The Migration Atlas: Movements of the Birds of Britain and Ireland (T. & AD Poyser, London).” (2002).
8. http://democracy.scarborough.gov.uk/documents/s63134/SCR1502%20GULLS%20FINAL%20REPORT%2020150309.pdf
9. http://www.rspb.org.uk/news/details.aspx?id=366903
10. http://www.birdlife.org/datazone/speciesfactsheet.php?id=3255