The nutritional carrying capacity of Scots pine woods for Capercaillie
Background and rationale
The Capercaillie (Tetrao urogallus), is a rare but important high profile component of the biodiversity of Scottish native pinewoods. They rely heavily on eating pine needles from autumn to spring. Food availability is usually the key determinant for population size in birds but despite the superabundance of pine needles for capercaillie, relatively few trees in a woodland are used consistently by them for feeding or roosting. This suggests that the operational amount of habitat available to them is much less than the total area available.
Capercaillie are known to be sensitive to qualitative aspects of the habitat and food, which is high in fibre and plant defensive compounds, including monoterpenes.
We know that the Scots pine trees used by capercaillie have lower concentrations of the monoterpenes, α-pinene and β-ocimene, that are strongly genetically controlled, but higher concentrations of magnesium in their needles (Fig 1). Some other determinants of the capercaillie’s association with trees within woods are known e.g. tree species, woodland structure, tree structure, proximity to tracks and escape routes from roosting sites. However, our lack of understanding of the relative importance of these factors, particularly in relation to forage quality, may underlie the failure of capercaillie to recover their numbers, that currently fluctuate between 1000 and 2000, despite considerable conservation effort.
Aim/Scope
This study will quantify and integrate the multiple determinants of foraging and range quality for capercaillie. The specific aims are:
- i) to investigate the extent to which capercaillies exercise diet selection among trees within woodland and between major types of coniferous woodland.
- ii) assess if Scots pine woods represent a fine grain mosaic of suitable and unsuitable trees for foraging, superimposed on other determinants of tree suitability including tree location and morphology, nutrient content, and secondary metabolite concentrations.
- iii) identify the relative importance of these variables and iv) thereby predict the nutritional carrying capacity and habitat suitability of a range of coniferous woodland types.
Methods/Approach
Methods will include field surveys of the intensity of use of trees in association with quantification of their chemical and nutritional characteristics, morphology and landscape context, including suitability for predator avoidance, proximity to suitable neighbouring trees etc. The digestibility of different Scots pine chemotypes and other conifer species will be measured by using the ratios of indigestible markers (long chain hydrocarbons) in the food and droppings. This will be carried out for free-living birds, after verification that samples collected in the field, resulted from feeding on the tree where droppings were found, which is likely, due to very rapid digesta passage rate.
Staff involved
PhD Studentship: Currently vacant
Supervisors: Glenn Iason, Bob Mayes (James Hutton Institute), Steve Redpath (University of Aberdeen), Ron Summers (RSPB).
Funding
This research is funded by the James Hutton Institute studentship fund, Aberdeen University and the RSPB.
