Generally speaking, deer are secretive mammals that are acutely sensitive to humans (or predators) sneaking around in the undergrowth; even where they dwell in or close to large human settlements, they can be difficult to spot. Moreover, deer often live in dense woodland/plantations or remote hillsides, which can make accurate surveys difficult. The habitat in which they live contributes directly to the degree of ‘critical resource stress’ (i.e. some resource necessary to survival is in short supply) that the animal is exposed to, which regulates breeding success and ultimately controls population productivity. Thus, it is not difficult to understand that they are hard to survey, making it a challenge to obtain accurate information about numbers and population demography (i.e. size, structure and overall changes in populations with time). Over the years many have tried to estimate deer numbers in Britain, but only recently—with the aid of large networks of scientists and volunteers using various techniques from counting droppings to radio-tracking and thermal imaging—have we started to get a handle on deer numbers.
In a 2005 paper to the journal Mammal Review, British Deer Society (BDS) biologist Alistair Ward presented an analysis of data collected by the BDS between 1969 (their first attempt to survey British deer populations) and 2002. From the survey data, Ward estimated that Red deer numbers had expanded at a compound rate of 0.3% per year, the lowest rate for the six species studied. The range expansion of Red deer in England and Scotland (recording efforts in Wales and Northern Ireland prior to 2000 were too low to provide a true picture of deer expansion) had also been much slower, and the total area into which they’d expanded was smaller, than for most of the other deer species.
Ward suggested that, although Red deer use woodland throughout much of their range, the thick abundant new woodland plantings may offer less suitable habitat for them than other species (e.g. Roe deer, Capreolus capreolus), while the large urban gardens and parks that have assisted the spread of species such as the Roe and muntjac (Muntiacus reevesi) are probably unsuitable for Red deer and may even represent a physical barrier that prevents or hampers their spread.
The data analysed by Ward also revealed that Sika deer (Cervus nippon) had encroached significantly into the range of the Red, occupying 41 (7%) of the 10 km survey squares in the Red’s range in 1972 and 275 (36%) by 2002 – Ward described this as a “trend that causes concern”. By comparing the country-wide estimate of Red deer numbers provided by Steve Harris and colleagues in their 1995 JNCC publication A Review of British Mammals (360,000 animals) to the numbers estimated to be present in Mesolithic (12,000 to 3,000 B.C.) Britain, however, Ward concluded that their numbers were “closer to their former population sizes than they have been for centuries”.
In their UK Mammals: Species Status and Population Trends report, published in 2005, the Mammal Tracking Partnership gave estimates of Red deer numbers in Scotland, England, and Wales of 347,000, 8,000 and fewer than 500, respectively; this put the overall figure for British Red deer at about 355,500, close to the estimate given by Harris and colleagues a decade earlier. The UK Mammals report also noted that the population in Scotland appears to have been increasing steadily since 1969 and, although it may now have stabilised, Red deer are increasing in both range and number across the south and west of England.
In the 2008 Mammals of the British Isles: Handbook, Brian Staines, Jochen Langbein and Tim Burkitt reviewed the population literature and arrived at a figure of between 335,350 and 366,110 Red deer in the major populations within the British Isles. A breakdown of their data suggests that the vast majority of these (some 95%) live on the hillsides and plantations of Scotland. These figures tally with the Parliamentary Office of Science and Technology’s POSTnote, published in February 2009, which gave a population estimate for Red deer of “>350,000”. The POSTnote gave the same estimate of population growth as Ward’s 2005 appraisal: roughly 0.3% per annum.
The results of the British Deer Society's 2016 deer survey suggest that the Red deer has expanded into some areas, to the east of the Lake District for example, while others have receded, as appears to be the case for the population in the Galloway Forest region of southern Scotland. Broadly speaking, the species appears to be slowly expanding its range, although there are no new data on which to base population estimates. The most recent attempt of which I am aware was the broad-scale review of the literature Simon Croft and colleagues used in their 2017 PLOS One paper to model populations of all Britain's mammals. Their analysis, based on published densities in various habitat types, estimated between 380,000 and 781,000 Reds in the UK and at least a 5% increase since the 1995 estimate. The authors do concede, however, that a lack of density information from England may well have overestimated the population.
Red deer in Ireland
The situation in Ireland is less clear than in Scotland or England. There were insufficient survey data for the UK Mammals report to estimate deer numbers here and neither the POSTnote nor Staines and his co-authors make any specific reference to Irish numbers. The Wild Deer Association of Ireland (WDAI) doesn’t offer an overall estimate of numbers although, on their website, they do note that there were 690 Red deer in the Killarney National Park during the mid-1990s. An article in the Irish Examiner in May 2017 put the figure in the park at 700, although they don't provide a source.
More recently, in February 2009, several newspapers carried the story that Ireland’s authorities (in this case the Irish Farmers’ Association, Irish Deer Society and WADI in conjunction with the government) were planning a widespread cull of deer. The quotations carried by the newsmedia didn’t provide details as to the number of different species, but they did suggest that upper estimates put the total number of deer in Ireland at around 100,000. Despite this, on their website, the Irish Deer Society point out that: “It is not known how many [deer] there are in Ireland as no national comprehensive survey has been done.”
It should be noted that a drawback to using national estimates of population figures is that they can mask local trends. and its these that are vital for appropriate management of the country's deer population.
In the New Forest, for example, numbers have fluctuated considerably even to the point of this species disappearing from the Forest altogether. Currently, the Forestry Commission aims to maintain the Red deer population on the Crown Lands (the area over which they have jurisdiction) at around 100 animals. In his 1972 book on the subject, Eric Lloyd estimated that there were 500 to 800 Red deer on Exmoor, a figure that was increased to between 700 and 900 by Gordon Miller, John Miles and Bill Heal in their 1984 A Study of Exmoor, and upped again by Noel Allen in his 1990 book Exmoor’s Wild Red Deer, who put the figure at around 1,500. Today, the Exmoor National Park Authority estimates that there are some 3,000 Red deer on the farms, woodland and moorland of Exmoor.
A report published by the Royal Society for the Protection of Birds and what was the World Wildlife Fund (now World Wide Fund for Nature) in 2003 suggested that, after massive declines in numbers up to the 1800s, deer populations in the Scottish Highlands have now exploded; the report cites an increase from 300,000 in 1989 to 450,000 in 2002. In a brief communication to the journal Nature during 2004, however, Tim Clutton-Brock, Tim Coulson and Jos Milner argued that the Scottish deer population is unlikely to be increasing by such a startling rate, pointing out:
“A large part of the apparent increase [given in the RSPB/WWF report] is due to the arbitrary tripling of the estimated number of deer living in woodland, where they cannot be counted reliably.”
Different habitats, different numbers
Rather than trying to come up with a total figure, stalkers and biologists instead generally opt for a density - a sustainable number of deer per unit area. Deer density varies considerably in response to the distribution of resources and how connected a landscape is to allow colonisation. Broadly speaking, the number of deer that live in an area is dependent upon the resources therein and this is significant in explaining the considerable variations we see in density across the country. The Mammals of the British Isles: Handbook provides estimates of 10 to 15 animals per sq-km in major deer forests and plantations, 20 to 25 per sq-km in Ireland’s conifer woods, nine per sq-km on open hillsides and in excess of one hundred per sq-km on some winter ranges. In their 1993 Field Guide to Mammals of Britain and Europe, David Macdonald and Priscilla Barrett give population densities of between five and 45 animals per square kilometre, depending on the habitat, while Croft and his colleagues gvae between 0.69 (i.e. one deer per 1.5 sq-km) and 28 per sq-km.
A summary of the fluctuation in Red deer numbers in Britain as a result of human interference and management can be found in the Interactions with Humans section.