Developing Conservation Strategies For The Chough In Scotland
Published on 7 May 2010 in Ecosystems and biodiversity
Introduction
The red-billed chough (Pyrrhocorax pyrrhocorax) is classed as being of high European conservation priority and the islands of Islay and Colonsay hold virtually the entire Scottish population of this species. As a consequence, parts of both islands have been designated as Sites of Special Scientific Interest and Special Protection Areas to reflect the occurrence of chough.
There is also a requirement placed on EU Member States to establish appropriate schemes and management actions to ensure the health of populations of species of conservation concern. The aim of this project (which was conducted between 2006 and 2009) was to further enhance knowledge of chough ecology on the island of Islay and thereby help develop a conservation strategy for choughs that could potentially be implemented via the Scottish Rural Development Programme (SRDP).
Key Points
The number of breeding pairs of choughs on Islay has varied over the last 25 years and was estimated at approximately 55 pairs in 2007. Adult breeding success and survival have remained relatively stable. However, first-year survival rates during 2007-2009 were lower than any observed during 1983-2007. Were the rates of survival and breeding success observed in recent years to continue, the number of choughs breeding on Islay would be expected to decrease over coming years.
During 1983-2005, variation in the survival of sub-adult choughs was correlated with variation in local weather (specifically, temperature and rainfall) and indices of the abundance of leatherjacket grubs in grassland (based on large scale surveys of annual variation in leatherjacket densities in south-west Scotland conducted by SAC). Although correlation cannot prove direct causation, these data indicate that among-year variation in sub-adult survival may be caused by large-scale variation in weather and food abundance. These factors are difficult to manage directly but might be minimised or ameliorated by appropriate management of the habitat surrounding nest sites.
Specific areas of Islay have been particularly important in maintaining the island’s chough population over the years. In some of these areas breeding success has been poor in recent years, possibly associated with a decline in the condition of existing nest sites. It would therefore be prudent to provide and maintain suitable nest sites and foraging habitat in the areas of Islay that have consistently produced choughs that survive well.
On Islay, c. 90% of observations of foraging flocks of choughs during April 2006 - March 2008 were in areas associated with coastal dune systems. Sub-adult choughs used a variety of habitats within and around these areas, including grazed and largely ungrazed dune grasslands, kelp beds, bare sand, cliff and heath. Coastal dune systems are therefore of major importance for sub-adult choughs on Islay and should be maintained in a state that maximises the abundance and availability of the chough’s invertebrate prey.
Most of the remaining c.10% of observations of foraging flocks of choughs were in newly cut silage fields. This habitat was used by a substantial proportion of newly fledged and sub-adult choughs during June-August, and is likely to provide an abundance of food for newly fledged young. The extensive use of this habitat when available suggests that cut silage fields can be a highly profitable foraging resource for sub-adult choughs, particularly in summer (a time when sub-adult mortality can be high). Both the timing of the closing off of fields to grazing animals, which influences the pattern of change in grass length, and the timing of the silage cutting, therefore influences foraging opportunities for choughs.
Research Undertaken
This research was undertaken by Dr Jane Reid (University of Aberdeen), Professor Pat Monaghan, (University of Glasgow), Dr Eric and Mrs Sue Bignal (Scottish Chough Study Group) and Dr Davy McCracken (Scottish Agricultural College). Dr Maria Bogdanova was employed as a postdoctoral research assistant on the project. Funding was provided by a Knowledge Transfer Grant from the Natural Environment Research Council (NERC), with matching partnership funding and in-kind Scottish Natural Heritage (SNH) and the Royal Society for the Protection of Birds (RSPB).
The overall aims of the project were to develop the scientific understanding of the population ecology of choughs on the island of Islay, and to use this understanding to inform the development of appropriate conservation strategies and policies. The project built on existing long-term research on Islay’s choughs, particularly a long-term colour-ringing programme run by the Scottish Chough Study Group since the early 1980s.
The research involved further analyses of the long-term data, plus two years of intensive fieldwork designed to answer specific questions. The work aimed primarily to understand the ecology of choughs in their sub-adult years (i.e. from fledging to breeding age). Survival from fledging to breeding is a key factor in causing population change. However, relatively little was previously known about the behaviour and ecology of choughs during this time in the life-cycle.
Policy Implications
Due to the low rates of sub-adult survival during 2007-2009, the number of choughs breeding on Islay is expected to decrease over the next 2-3 years. The status of the chough as being of high conservation concern should therefore be maintained in Scotland and conservation and agri-environment policies should reflect this status.
Successful conservation of choughs on Islay is likely to rely on appropriate management of the main flock foraging areas (i.e. the main dune systems and, where relevant, early-cut silage fields) and individual breeding territories. The management aim should be to generate a diversity of habitats that support high plant and invertebrate diversity, thereby increasing the range of foraging options that will be available to choughs at any point in time. There should not be a focus on the provision of any single food resource by overemphasis on any single management approach.
Over the coming years, the main mechanism available for funding appropriate conservation management for chough will be through developing appropriate farm-level applications to the SRDP. There are currently no chough-specific options available within the SRDP and the introduction of any such new options will require approval from the European Commission. In the medium to long term, consideration needs to be given not only to what such chough-specific options would consist of but also what the potential impacts of any such chough-specific measures would be (since it would not be desirable to produce simple, uniform habitats rather than the complex diversity that seems to be required).
In the short-term, the conservation importance of choughs in Argyll should be emphasised by a combination of raising the profile of choughs more within the SRDP application process and also directing prospective applicants from Islay and Colonsay to those existing options that are of direct relevance and potentially beneficial for choughs. These existing chough-relevant measures also need to be drawn to the attention of agricultural and conservation consultants who draw up SRDP applications for Islay and Colonsay.
There is presently no provision for biological (as opposed to basic compliance) monitoring within the SRDP. To ensure that impacts can be measured and appropriate changes can be made to future SRDP plans, the biological outcomes of existing plans need to be monitored (using appropriate biological metrics) over and above the basic compliance monitoring that individual farms may or may not receive. In the immediate term, monitoring of outcomes should be prioritised on the major dune systems that are essential for sub-adult choughs.
Adequate nest and roost sites need to be maintained and/or provided in key areas of Islay. The easiest means of resourcing nest and roost site maintenance and provision on those farms which fall within designated areas is to include this work within the SRDP plans (since the SRDP allows for funding capital works on designated sites). An additional mechanism needs to be put in place to either justify the funding through the SRDP of nest site repair/provision on farms outwith designated sites or identify appropriate funding sources that could be utilised in such instances.
Author
Dr Davy McCracken, SAC Davy.McCracken@sac.ac.uk
