Causes of decline of common scoter (Melanitta nigra) in north Scotland: evidence from palaeolimnology

• Main Author: Robson, HJ
• Other Authors: Jones, VJ, Sayer, CD, Brooks, SJ, Hilton, GM
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UCL (University College London) 2017
• Subjects: Melanitta nigra
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10039205/1/Thesis-H-J-Robson.pdf; https://discovery.ucl.ac.uk/id/eprint/10039205/

The common scoter (Melanitta nigra) is a UK priority species that has experienced severe declines in breeding numbers over the last 30 years. The Flow Country in north Scotland is an internationally important wetland, where the decline of iconic species, such as the common scoter, is particularly concerning. This thesis takes a unique approach to investigating the causes of waterbird decline by combining detailed contemporary ecological data with geospatial modelling and palaeolimnological reconstructions. Detailed surveys were undertaken to characterise the current physical, chemical and biological conditions within 18 Flow Country lochs. These data were used for exploratory analyses and as explanatory variables in a general linear model that examined the predictors of common scoter loch value (SLV). Statistically significant predictors of SLV proved to be dissolved organic carbon, water depth and sediment type. The landscape scale features associated with common scoter distribution in the Flow Country were explored using a species distribution modelling (Maxent) approach. Influential landscape features were found to be proportion of surrounding forestry close to a loch, the soil moisture and bedrock geology. Two theories for common scoter decline were developed using these contemporary data sources; (i) the competitive balance between brown trout and common scoter has altered in recent decades, resulting in less food, (ii) the physico-chemistry of lochs has been altered by afforestation adversely affecting physical loch structure and/or invertebrate food supply. Theories for decline were explored using two palaeolimnological approaches. Multi-proxy top-bottom analysis of cores from 18 lochs demonstrated that these are dynamic environments which have undergone substantial change over the last 150-200 years. Multi-proxy analysis of high temporal resolution cores from four lochs indicated that the study sites have gradually become more productive over the last 150 years, with a distinct shift towards more ...