Species Spotlight - Little Tern Sterna albifrons

Little Terns at Gronant, July 2005, © Jim Armstrong

Little Terns are a declining species in Britain and Ireland and they are amber listed in the Bird of Conservation Concern list (1). It is estimated that they have declined from about 2,850 pairs in 1987 to less than 2,000 today, a worrying trend. The RSPB reckon that this drop in numbers is due to poor productivity at the nesting colonies, mainly because of an increase in fox numbers (2). However, it is not all doom and gloom as our local colony at Gronant is doing very well as demonstrated in the graph below, this shows the numbers of pairs and young fledged each year since 1975 when the RSPB started wardening here.

As is typical of tern colonies nesting success can vary greatly from year to year, and that has always been the case at Gronant with the difference between 2001, when just one young fledged, and 2003, when a record breaking 190 young fledged, an extreme example of this.

Why is nesting success so varied? Two factors in particular are important, weather and predators. If the weather is bad at crucial times, such as when the bulk of the terns first arrive, when they first lay eggs and when the eggs first hatch; this can make a huge difference, with sand blowing over the nests the most harmful effect of windy conditions.

The three main predators at Gronant are crows, kestrels and foxes. Crows can certainly take a large number of eggs, but are relatively easy to scare away so this is where wardening is crucial, particularly early morning when they are most active. One of the problems in recent years is that as the colony has grown the area to cover has got bigger - if you are scaring a crow at one end of the colony you haven't a hope of stopping one taking eggs at the other end, so the relatively recent innovation of having more than one warden on duty is essential. In contrast a determined Kestrel is very difficult to stop, a male in 2001 with a hunting technique more like a Sparrowhawk took around 60 chicks, that's an average of two successful hunting trips a day over a thirty day period. But even a Kestrel can be deterred by distracting it with a loud whistle just as it is diving down towards the colony, and again the role of the wardens is crucial here. The Little Terns themselves can be pretty effective chasing away avian predators, they can get particularly aggressive after the chicks have hatched. Even more effective are Oystercatchers, we usually have a couple of pairs within the colony, it is quite amusing to see a crow suddenly turn tail with a couple of very annoyed Oystercatchers in chase!

Foxes take both eggs and chicks and if a couple get into the colony they can more or less wipe it out in one night, if given the chance. But here we have a big success story at Gronant with the introduction of a new and very effective electric fence three years ago, since when foxes have gone from being the most serious predator to not one single record of fox predation within the fenced area for three years!

The first Little Terns arrive back at Gronant late April/early May, although no serious nesting attempts are made until the last week in May. By the second week in June there is usually a significant increase in birds, called the 'second wave' by the wardens, and these soon get down to egg laying. The incubation and fledgling period are each around 20 days, with the first chicks fledged around the first week in July and the majority flying by the end of the month. It is during July we get a third wave of birds arriving, in 2005 numbers increased from the 150 or so breeding birds to over 400 in total. Some of these may be from colonies further north, but the majority are likely to be returning two year old birds not yet ready to breed. In 2005 these two year old birds will have been fledged from the record breaking 2003 season when 190 chicks successfully flew. From mid-July onwards numbers in the Dee Estuary itself start to increase, with peak numbers usually occurring in the first two weeks of August. The calm shallow waters of the estuary act as a nursery for the terns with the sand banks around Hilbre being particularly attractive, 300 or so are often recorded here at this time with good size flocks also seen at Point of Ayr, West Kirby and Hoylake - no doubt many of these will be from Gronant.  

The Gronant Little Tern colony is one of the most productive in the UK as shown in the bar chart above, 2004 was a particularly good year at Gronant, 2003 even better, and even though 2005 was relatively poor the terns still produced 35 fledglings. The selection of other colonies from the UK in 2004 shown in the bar chart were actually some of the best in the country, the original table (3) showing all the main colonies make depressing reading with 18 out of 32 colonies not producing a single chick. Colonies in Ireland, however, fared much better with a similar success to that obtained at Gronant.

I hope I have made it clear the vital role the wardening scheme has played in the success at Gronant. Denbighshire Countryside Service are organising the wardens this year, so if you want to volunteer email Garry Davies at garry.davies@denbighshire.gov.uk. Garry can also be contacted by phone - 01745 356197 or 07884490345.  

Acknowledgments.
I'd like to thank Gareth Stamp (RSPB) for providing me with the line graph above in 2001 which I have subsequently updated.
Thanks to Jim Armstrong for letting me use, once again, his wonderful Little Tern photograph.
Much of the data for the article, including the bar chart, was taken from the Gronant Little Tern Report 2005 written by James Armstrong and Shane Hughes, this report is packed full of information about Little Terns both at Gronant and nationwide.

References.
1. The population status of birds in the UK - http://www.rspb.org.uk/Images/Bocc2_tcm5-44622.pdf
2. Diagnosis of the population decline of Little Terns - http://www.rspb.org.uk/science/Ecology/2002/littleterndiagnosis.asp
3. James Armstrong & Shane Hughes, Little Tern Colony - Gronant Dunes, 2005.

Richard Smith

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