Diver ecology (Scotland)

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Adult Red-throated divers and chick

The UK red-throated diver breeding population of approximately 1300 pairs constitutes about a third the EU total. It is restricted to Scotland, with the highest densities in Shetland, the Outer Hebrides and Orkney. Despite breeding population fluctuations in the UK and declines in other parts of its European breeding range, there has been relatively little research into the factors affecting breeding performance and population stability compared with other seabirds breeding in the region. Studies in Scandinavia and North America have linked population declines to reduced prey availability, disturbance at breeding sites and pollutants, especially mercury, but little is known of the extent to which these factors affect the UK population. Climate-space-modelling evidence indicates that red-throated divers are likely to be highly sensitive to climate change, with one leading study predicting their disappearance as a UK breeding bird by the end of the century. Ironically, renewable energy developments aimed at reducing CO2 emissions and limiting climate change are themselves a potential serious new threat to divers. Windfarms, both onshore and offshore, and tide and wave energy developments may lead to mortality through collisions or displace birds from breeding or feeding habitat.  There is an urgent need to understand the effects on divers of renewable energy developments, especially those in the marine environment, so that risks to divers can be minimised.  

 

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Red-throated diver's nest with one egg

Natural Research has undertaken research on breeding divers in Lewis, Orkney and Shetland since 2002. The research includes work to quantify the risks posed by wind turbines to flying divers on their breeding grounds and a 3-year doctoral study in association with Glasgow University developing state-of-the-art monitoring techniques and looking at the determinants of breeding success in Shetland. The ongoing Shetland breeding study covers approximately 100 pairs annually and is becoming increasingly interesting as additional years allow longer term trends to be identified. Natural Research is also currently planning research to investigate the effects of marine renewables on divers, particularly developments located in the coastal feeding areas close to breeding grounds.

Simon Hulka's PhD completion

Simon Hulka has recently completed his PhD thesis at the University of Glasgow entitled 'Red-throated diver breeding ecology and nest survival on Shetland'. The PhD is part of ongoing studies funded by Natural Research looking at red-throated diver biology, aimed at better understanding the potential impacts of renewable energy developments on the species. The PhD research developed state-of-the-art monitoring techniques and used modern nest survival modelling to identify and determine the relative importance of factors influencing breeding performance and nest survival in red-throated divers.

The study confirmed earlier research indicating that red-throated divers are most susceptible to breeding failure during the egg stage, and identified early incubation as a particularly vulnerable period. This was probably due to low quality birds failing soon after laying coupled with increasing investment by adults in nesting attempts that survived for longer, rather than differences in predation risk between the incubation and chick-rearing stages. The study also indicated that higher individual quality, breeding early in the season or during relatively wet and windy conditions resulted in higher nest survival rates. Taken together, these findings suggest that predation risk is a key factor determining red-throated diver breeding performance, with breeding pairs more successful when predation risk is low, or if pairs are able to minimise the risk. In other research for the PhD, distinct patterns of nest attendance both through the day and at different stages of incubation were found using data from temperature loggers installed in the base of nests.

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Pair with intruder

In addition to findings relating to breeding ecology, the PhD research developed minimally-invasive new techniques to determine timing of breeding using photographic measures of chick size and characteristics of nest temperature around the time of hatching. Employing these techniques in future will improve the accuracy of productivity and nest survival estimates and minimise disturbance during the breeding season. Patterns of nest attendance identified during the study indicate vulnerable periods during the day and during incubation, and are directly relevant to construction activity and operation of terrestrial and marine wind energy developments located in red-throated diver breeding areas. The importance of individual or nest site quality in determining breeding performance highlights the need to monitor fish prey abundance in breeding and non-breeding marine foraging areas as well as changes in the characteristics of available breeding lochs as an integral part of a conservation strategy for the species.

A copy of Simon's PhD is available to view here

Photos: Top: S. Hulka Bottom: D. Jackson

This project is being undertaken in collaboration with D. Okill of the Shetland Ringing Group.

For further information please contact info@natural-research.org

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