Pine marten (Martes martes) distribution and abundance in Ireland: A cross-jurisdictional analysis using non-invasive genetic survey techniques

1. What they did

Pine martens live at the western edge of their world range in Ireland, one of the least forested regions in Europe. They declined heavily over the 19th and 20th centuries through forest loss, poisoned baits, persecution and trapping for fur. Before this study there had been no survey covering both the Republic of Ireland and Northern Ireland, and nobody knew how many martens there were.

The authors set out to map where pine martens live now, see how this has changed in about 30 years, and make the first estimates of their numbers:

• Scat surveys. In June to September of 2005 to 2007, they walked an average of three transects of about 1.5 km in forest or scrub within each of 258 squares of 10 km by 10 km (228 in the Republic and 30 in Northern Ireland). In all, 762 transects covered over 1200 km. Each transect was walked once, only in good weather. They collected scats that looked like pine marten scats by their shape, plus any uncertain ones: 765 scats in total.
• DNA testing. Because of limited funding, they tested the most likely pine marten scat from each square first, and tested further scats only until one was confirmed as pine marten.
• Comparison with the past. For 183 squares in the Republic they compared their results with a 1978 to 1980 survey that relied mainly on scat identification, plus sightings and local knowledge.
• Core range and numbers. They mapped a core range (areas where at least 90% of surveyed squares had martens) and estimated numbers by dividing the occupied forest area by the average territory size of seven radio-tracked martens from an earlier Irish study (about 154 ha).

2. What they found

Where martens are

• Pine martens were confirmed in 153 of 258 squares (59.3%): 59.6% in the Republic and 56.7% in Northern Ireland.
• They were concentrated in the west and midlands of the Republic, with scattered populations in the southwest, southeast and east. They were largely missing from the south and southeast of the Republic and most of Northern Ireland.
• Of the 105 squares without martens, no scats were found in 45, and the scats collected in the other 60 were not from pine martens.

Change since 1978 to 1980

• In the comparable squares, occupancy rose from 28.4% to 63.9%, a significant increase. 68 squares changed from no martens to martens, and 4 the other way.

Core range and numbers

• Core range covered 51.5% of the Republic’s land area, 18.3% of Northern Ireland and 45.9% of the island.
• Estimated numbers: about 2740 pine martens in the Republic (90% confidence interval 1350 to 4330) and about 320 in Northern Ireland (160 to 510).

3. What they concluded

• Pine martens have expanded their range in the Republic over the last 30 years, probably from refuges in the west. Three likely reasons: forest cover nearly doubled since 1980; legal protection since 1976; and reintroductions, such as up to 30 martens released in Killarney National Park from the late 1980s to the mid 1990s. Relocations of “problem” martens and changes in red fox numbers may also play a part, but data are lacking.
• Even so, the present range is still much smaller than in the past, and the expansion happened without any planned conservation action.
• In Northern Ireland there is little or no sign of expansion despite legal protection and more forest. Small, fragmented populations may face barriers such as small numbers, poor survival when dispersing and illegal persecution. With numbers in the low hundreds, the authors call for a conservation strategy there immediately.
• Earlier assessments that rated the species as of least concern were partly based on estimates of 3000 to 10,000 martens; this study found fewer than 3000, so a reassessment seems prudent.
• More basic research is needed on abundance, social and spatial behaviour, habitat selection, breeding, survival and the effects of forestry.

4. How tracking was or was not used

The survey was a sign survey: observers walked transects looking for pine marten scats and picked them out by their shape. DNA testing then confirmed which scats were really from pine martens. The authors chose DNA confirmation because earlier scat surveys that relied on shape alone had been criticised for identification errors. No footprints or other signs were recorded, and no trailing was reported.

5. Tracker or observer certification

Reported but not validated. The senior author surveyed 216 squares (84%) and “trained field staff” surveyed the other 42 (16%). No certification or skill test is described. The paper does not report how many collected scats were correctly identified by shape, so observer accuracy cannot be judged from it.

6. Other technologies, skills or innovations

• A real-time DNA test that tells pine marten scats from red fox scats.
• A screening approach that tests scats one at a time per square until a pine marten is confirmed, to save costs. The authors note that this means scat abundance and habitat use could not be analysed at the transect level.
• Scats were bagged by turning a zip-lock bag inside out, to avoid contaminating the DNA, and stored frozen.
• Mapping in a Geographic Information System (GIS).

7. Implications for conservation (from the paper)

• Both jurisdictions need conservation strategies for pine martens, to secure the recent expansion, support further expansion and reduce conflict that could lead to illegal persecution.
• Returning martens may come into conflict with game rearing, livestock and the management of other species, especially birds. Management plans should accept that some predation is a natural part of a stable predator and prey system.
• Short-rotation commercial conifer plantations are the main habitat, and the effects of timber harvesting and of small, scattered private plantations are not understood.
• Regular monitoring is required by international obligations but may be limited by funding.