Using cohort analysis to reconstruct the size and structure of deer populations in forestry with special reference to roe deer (Capreolus capreolus L.)

Abstract

SummaryThis paper describes an attempt to assess retrospectively the numbers and demography of a population of roe deer (Capreolus capreolus L.) on an estate and its contiguous area of forestry in North Cumbria, England, amounting to 968 ha, of which 285 ha was woodland. After ageing all the jaws of deer which had been culled or found dead over a period of 29 years (359 deer), populations were reconstructed for each of the earlier years using cohort analysis. Excessive immigration of bucks onto the area of newly planted woodland and the absence of resident does for the first 8 years limited the analysis to one part of the estate (Kingfield) with assessments for the years 1972-1997. As mortality data for Kingfield were limited (222 deer), they also magnified the effects of gains and losses through migration. As a result, and because the area was surrounded by forestry with only lightly culled deer populations, immigration by non-territorial bucks caused some difficulty in assessing the real population in the earlier years. At first sight therefore, these results would appear to negate the usefulness of cohort analysis to determine the numbers of deer in forestry. They do, however, demonstrate quite clearly that, as long as virtually complete mortality data are collected, even with small numbers reasonably accurate assessments of previous populations can be obtained. The most reliable analyses for the whole period were those of the does and female kids, the only real residents. Using these data and those of the bucks for recent years, the probable levels of stocking latterly amounted to 48.8 deer km -2 in plantations of all ages, or 60 deer km -2 in woodland >13 years after planting. The density of deer was also shown to have been positively and significantly (P ≤ 0.001) related to the area of woodland >13 years after planting (<40 ha in 1972, 70 ha after 1993). Moreover, it is now possible to set more realistic targets for the culls on the estate at ~40 per cent of the reconstructed populations, amounting to an annual cull of 19.5 deer km -2 of Forestry, Vol. 76, No. 4

Influence of weather and phenotypic characteristics on pregnancy rates of female roe deer in central Italy

“…Females of less than a year were not included in the analyses, because breeding activity in females occurs when they are at least 14 months old . For each female, we recorded day and locality of harvesting, reproductive status (presence and number of foetuses), eviscerated body mass (measured to the nearest 0.1 kg) (Bekenov et al 1998;Hewison and Gaillard 2001) and age (estimated according to tooth wear and eruption) (Lowe and Thompson-Schwab 2003).…”

Application of Cohort Analysis to Large Terrestrial Mammal Harvest Data

“…Originally developed in fisheries science (Gulland 1965;Pope 1972), the technique has been applied to commercially harvested fish stocks (bigeye tuna Thunnus obesus, Nishida and Takeuchi 1999; chub mackerel Scomber japonicus, Yatsu et al 2002; Pacific cod Gadus macrocephalus, Ueda et al 2006), aquatic mammals (sperm whale Physeter macrocephalus, Shirakihara 1991; minke whale Balaenoptera acutorostrata, Fujise et al 2005; minke whale, Mori et al 2007) and terrestrial mammals (red deer Cervus elaphus, Lowe 1969; white-tailed deer Odocoileus virginiaus, McCullough 1979; marten Martes americana, Fryxell et al 1999; roe deer Capreolus capreolus, Lowe and Thompson-Schwab 2003). Cohort analysis is based on the principle that individuals born in a particular year (a cohort) will die either from natural causes or from harvesting (i.e., human exploitation) and that mortality may occur at any point in time up to the cohort's oldest age-class.…”