Related
Recommended
Wez Smith
  Yesterday, with help from staff and volunteers at both the RSPB and the Hampshire & Isle of Wight Wildlife Trust along with funding from the Hampshire Ornithological Society and EU Life, we started the process of having a seasonal tern nesting raft at the Oysterbeds within the West Hayling Local Nature reserve.  Although there's still some work to do, we're aiming to have it finished and ready to unveil by the time terns are prospecting for nesting sites in mid to late April.  I'll be writing a blog once it's ready to use and keeping you updated but I wanted to take a little time to give some background on why we're trialing a raft here and what we hope it might achieve.  The common tern & little terns at the Oysterbeds have been struggling in recent years as the mixture of breeding species changes and we'll be offering some of them the chance to nest away from their larger Black-headed Gull cousins this year in the hope that it will improve their fortunes.  
Above: Putting together the new raft at the Oysterbeds with the help of RSPB staff from nearby Pagham and also a team from the Hampshire and Isle of Wight Wildlife Trust (Photo: Louise MacCallum)
  The West Hayling Local Nature Reserve (also known as ‘the Oysterbeds’ due to its historic use cultivating Oysters) is an important seabird breeding site on the north east of Langstone Harbour.  During the 2016 breeding season, there were 686 pairs of Black-headed Gulls and 57 pairs of Common Tern nesting there.  All of this takes place on two linear islets within the central lagoon of the reserve.  The lagoon in which the islets sit is only partially tidal and remains flooded throughout the entire cycle, offering the breeding birds a relatively safe area undisturbed by people or ground predators.  The site is also close to the usually rich feeding grounds within the harbour offering appropriate food just a short flight away.

Above: The oysterbeds lagoon at sunset with the seabird colony islands in the centre.
  Due to the site's suitability for nesting seabirds, it has become a prime breeding location and is the first  seabird nesting location within Langstone Harbour to be settled each year (with Black-headed Gulls often forming territories in late February).  As a result of this, most of the available nesting space is taken up long before migratory terns arrive back from their African wintering grounds in April.  Once terns do arrive however, they still show a preference for this site but are forced to locate within gaps in the gull colony, limiting their numbers.  More importantly, the terns productivity (a measure of fledglings raised per nest) is curtailed almost completely due to opportunistic predation of chicks by gulls only a metre or less away!  

Above: Common Terns looking for nesting spots amongst the well developed Black-headed Gull Colony (Photo by Chantelle Barry)
Although common terns will choose readily to nest by Black-headed Gull colonies (potentially for the protection they offer from larger predators), the sheer density of nesting here due to the very limited available habitat appears to be causing them issues.  Along with erosion of the islets and some periods of difficult food supply, this has resulted in an ongoing decline of the common tern colony here with the only chicks surviving to fledging age being those that hatch at the end of the breeding season once the earlier nesting gulls have abandoned the site.  Since 2014, this means just 5 common tern young have fledged here (compared to 1632 Black-headed Gull chicks)!
Breeding pairs of Black-headed Gulls and Common Terns at the Oysterbeds.
Species
Breeding Pairs 2014
Breeding Pairs 2015
Breeding Pairs 2016
Black-headed Gull
677
627
686
Common Tern
96
88
57
 
 Although there are several potential solutions to the tern productivity issues here, the only option which presents itself as both easily viable and possible to implement in 2017 is the use of artificial nesting rafts.
‘Tern Rafts’ have been located at many nature reserves as well as urban areas throughout the world and have an extensive evidence base of success.  The concept is quite basic but addresses the habitat needs of common terns well.  Although they have a range of designs depending on location, most rafts share the following general principles:

·         A platform which floats above the waters surface.

·         A shingle/gravel substrate upon the top of the raft in which terns can form ‘scrapes’ (nest bowls).

·         A perimeter barrier preventing young chicks from ‘falling overboard’ until they’re old enough to be able to get back on as well as preventing predators from accessing the raft.

·         A method of immobilising the structure to prevent it from floating away.

 

For the situation at the Oysterbeds, the great thing about using 'tern rafts' is that they can be made available for nesting after the gulls have started nesting but just before the terns begin looking for nesting sites.  This means that we can provide nesting habitat to terns in their preferred hunting territory without having to compete with the gulls that have already nested.  As they’re not physically connected to the other nesting habitat, this also means that predators would have to travel via air or water to the raft in order to predate young chicks.  As much of the Black-headed Gull predation of chicks (terns or other gulls) is opportunistic and involves their immediate neighbours, it is hoped that this should significantly decline the amount of chicks taken.
  The raft has been placed in a location far enough away from the lagoons shoreline so that prospecting or nesting terns are not disturbed by visitors and also so that accessing them will require significant effort for ground predators (like a fox for example). 

Above: The raft in place at the Oysterbeds, just a bit more work to do... (Photo: Louise MacCallum)

  The design is based on the raft development carried out at other sites and has been put together in four sections by a local carpenter.  The top is covered in shingle substrate and the perimeter is enclosed with a steel mesh allowing visitors to see in whilst preventing young chicks from falling off when darting for cover or food from their parents.  Once completed, we'll be watching it carefully over the summer to see how much it's used and (hopefully) how successful it is!  Even in the eventuality that it's not successful this year, the raft has been designed and constructed in such a way that it can be reconfigured into 2 or 4 separate smaller rafts, giving us the option of trying it in a new location next year or even several.  With this now available, we're hoping to be able to offer good quality tern habitat in suitable locations in an efficient manner whilst we continue to look at longer term strategies for securing their future.