Seeking Sika
An element key to the effective management of any species is an understanding of populations, specifically, having an accurate estimate of population sizes and densities. Without this essential knowledge, attempts at population control of animals such as deer are likely to prove inadequate. Various methods exist to count deer, such as: distance sampling, spot counts, faecal pellet counts, and camera traps, to name a few. Each have their own advantages and drawbacks, therefore, improving the current methods and creating new strategies for use in the management of populations, to yield ever better approximations of animal numbers, is highly valuable.
The use of wildlife camera traps, has until only recently, been restricted to the capture–recapture analysis of species, which requires recognising individuals through identifying their unique markings. However, over the last few years, researchers from the Zoological Society London and the University of Leeds have been developing a new methodology for use with camera traps to estimate animal densities, through modelling the underlying process of contact between animals and cameras. Employing the “Random Encounter Model” (REM), this new technique produces accurate and reliable estimates of population density, but unlike other methods, is neither labour-intensive, nor time-consuming, and the only major cost incurred is that of the cameras used.
I began my doctoral research by familiarising myself with this method of censusing, starting with deploying a number of cameras in an area of mature Sitka spruce forestry in Northern Ireland. This conifer plantation is located on Colebrooke Estate in Country Fermanagh, and is owned by Lord Alan Brooke, 3rd Viscount of Brookeborough, to whom I am very thankful for his blessing and encouragement to undertake this work. Covering a range of habitats with access to large deer species (Sika, Fallow and Red), Colebrooke Park offers very affordable stalking rates, making it one of the best places for deer stalking in Northern Ireland. With an estimated head of between 250 and 300 sika deer on the estate, depending on the time of year and culling success, the dedicated syndicate have their work cut out. Given the number of sika, I was confident I would see plenty while conducting my field work. Turns out the sika had other ideas. Being elusive and shy animals at the best of times meant that if I wanted to see any, I would have to conduct my fieldwork in constant “stalking mode” – silent and invisible – an impossible task with heavy and cumbersome equipment.
Fortunately though, I had some non-intrusive cameras at my disposal, and unlike me, they were highly successful at detecting the deer and so captured some brilliant pictures. The trail cameras were positioned in 10 random locations within one section of pole stage forest, and were each left for 14 days, totalling 140 days, or 3360 hours for all cameras. Within this time, 61 independent deer detection events occurred, leading to an estimate of 33.3 deer per km2 within the field site. A previous estimate from several years ago, using the same model and methodology, in the same forest, resulted in a remarkably close figure of 32.2 deer per km2. This is a good indication that this method of surveying a wild population is likely to be fairly reliable, given that the population has been managed in the same way over the last few years, and that other factors potentially influencing the density estimate (e.g. forage, weather, poaching) are thought to have remained relatively constant over this time period. In addition, the head stalker of the syndicate suggests from experience that this is a good estimate, given the number of deer being removed from the population.
But like all techniques, the Random Encounter Model has its own disadvantages, and is also at an early stage of development. My research might begin to address some of the issues, and start to fill the knowledge gaps with regard to its application with deer.
Erfan Fadaei grew up with a love of nature, and a particular passion for wildlife, leading him to a degree in Zoology at the University of Manchester, where he graduated in 2014. During his degree, he undertook a placement for 9 months with Scottish Natural Heritage, working with the Hebridean Mink Project on the Isle of Lewis, Scotland, and aided in the eradication of American mink from the archipelago in an effort to conserve ground-nesting birds. There, he became familiar with deer stalking and some aspects of deer management, and decided to pursue his interests in conservation and wildlife management by focussing on deer in the UK. He is currently undertaking a PhD in native and invasive deer management at Queen’s University Belfast.