Slavonian Grebe breeding habitat assessment

Phase 1 - Sedge bed and shoreline sediment surveys

The first phase of this work involved a comprehensive field study of the sedge beds and shoreline sediment of Loch Ruthven (a current and historic Slavonian Grebe breeding stronghold in the UK), using a study carried out in 2008 (Denny & Cowie, unpublished) as a baseline, followed by an assessment of shoreline sediment on Loch Ruthven and eight other lochs in the surrounding area.

Bottle sedge (Carex rostrata), a common emergent aquatic plant, is the main species used for Slavonian Grebe nesting habitat in the Highlands, hence the primary focus species in this project, with the birds preferring to nest in sedge beds with moderate to dense cover. Any existing sedge beds at the study lochs were found to be comprised of mostly Bottle Sedge, although the presence and density of three other common aquatic species were also noted when carrying out sedge bed assessments at Loch Ruthven – Water Horsetail (Equisetum fluviatile), Common Reed (Phragmites australis) and Common Spike Rush (Eleocharis palustris).

The results from this work were used to highlight the existing sedge bed densities, composition and extent at Loch Ruthven and how these have changed since the previous study in 2008. Maps were also produced to display the distribution of different sediment types around each of the study lochs, to highlight areas where sedge beds could be installed or existing ones could be managed.

This phase of the work was completed by the end of November, and we were thrilled that Chris Tilbury (‘Saving Slavonian Grebes’ project manager, RSPB) approached us with a further desk-based study in relation to the project.

Phase 2 – Aerial photography shoreline sediment assessment

Using high-resolution drone imagery provided by Tracks Ecology, we gave a rough assessment of the suitability for sedge bed growth at 16 additional lochs around the Central Highlands, using the knowledge we had gained when carrying out the previous field surveys.

Bottle Sedge thrives in silt-dominated sediment, in water depths of up to one metre on a gently sloping gradient. We used these requirements as a basis for mapping polygons using QGIS around areas on the shoreline that looked like they may be suitable for sedge growth in the drone imagery. The RSPB also provided us with a useful wave fetch model to overlay onto the maps, meaning we could consider wave activity when highlighting areas that had potential for sedge bed growth, as more exposed areas with higher wave fetch would be less suitable.

The project was very enjoyable and gratifying to be involved with, presenting us with unique challenges that we are not usually faced with in our day-to-day survey work. It was fantastic to carry out work on a practical conservation project that tied together both ornithology and habitat surveying, and we are greatly appreciative to the RSPB for giving us this opportunity.