Obtaining nesting material presents an optimal foraging problem, collection of materials incurs a cost in terms of risk of predation and energy spent, and individuals must balance these costs with the benefits of using that material in the nest. The hazel dormouse, Muscardinus avellanarius is an endangered British mammal in which both sexes build nests. However, whether material used in their construction follows the predictions of optimal foraging theory is unknown. Here, we analyse the use of nesting materials in forty two breeding nests from six locations in Southwest England. Nests were characterised in terms of which plants were used, the relative amount of each plant, and how far away the nearest source was. We find that dormice exhibit a preference for plants closer to the nest, but that the distance they are prepared to travel depends on the plant species. Dormice travelled further to collect honeysuckle Lonicera periclymenum, oak Quercus robur, and beech Fagus sylvatica than any other plants. Distance did not affect the relative amount used, although the proportion of honeysuckle in nests was highest, and more effort was expended collecting honeysuckle, beech, bramble Rubus fruticosus and oak compared to other plants. Our results suggest that not all aspects of optimal foraging theory apply to nest material collection. However, optimal foraging theory is a useful model to examine nest material collection, providing testable predictions. As found previously honeysuckle is important as a nesting material, and should be taken account when assessing suitability of sites for dormice.

Characterisation of Dormouse Nests

Hazel dormice nests were obtained from six different sites (Site) throughout Southwest England (Figure 1) in collaboration with Devon Dormouse Group. A total of 42 summer nests (NestID) were used for data collection and analyses. Nests were located on five different species of tree, hazel, (Corylus avellana - 30 nests), oak (Quercus robur - 5 nests), birch (Betula pendula - 3 nests), beech (Fagus sylvatica - 2 nests) and hawthorn (Crataegus laevigata - 2 nests). Nests were separated by hand, and plant materials (Material) were identified using a microscope when necessary (Figure 2 a and b). For the five nests from Pitt’s plantation that were analysed at the nest site, we used a twig to move around the nest material to identify the species. Plant materials were separated by species (both bark and leaf), and we recorded, a) whether a species was used or not (Use), and b) the percentage of each species in the nest (Perc). In all nests hazel bark, honeysuckle (Lonicera periclymenum) bark (not leaves), and ‘grass’ (most likely bluebell (Hyacinthoides non-scripta), were used as long strips to provide nest structure. The main plants used in lining the nest were oak, birch, bramble (Rubus fruticosus), beech, ivy (Hedera helix), hazel leaves, and hawthorn. Overall usage of moss was high, but out of 23 nests that contained moss, 13 of them had a mass of moss shaped as a cup, which indicates that most likely the dormouse nest was built on top of an old bird’s nest, so moss use was not analysed further. Other plant species sometimes used in the nests were rhododendron (Rhododendron ponticum), sycamore (Acer pseudoplatanus), blackthorn (Prunus spinose), fern (various species), elder (Sambucus nigra), and mountain ash (Sorbus aucuparia). Each of these was used in only one nest, except for blackthorn which was used in four, so these species were not included in the statistical analysis. We measured the distance (Distance) of the eight most common plant species (honeysuckle, hazel, beech, birch, bramble, hawthorn, ivy, oak) relative to each nest. The distance, measured with field measuring tape, was taken from the circumference of the tree in which the nest box was situated to the circumference of nearest tree of the above eight species, whether or not the species was used in that particular nest. 

In the file the columns describe the data, but for Effort there is only data for nests where the plant material was used.