PECKIANA Volume 8 (2012) pp

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1 PECKIANA Volume 8 (2012) pp ISSN Predation by the edible dormouse (Glis glis) on British woodland birds breeding in dormouse nestboxes Roger Trout, Emma Mayo, Sebastian Perceau-Wells & Sarah Brooks Abstract Monthly examination of edible dormouse nestboxes in spring 2008 at a site in the Chilterns, England occasionally revealed nesting attempts by woodland birds. During the spring and early summer 2009, 2010 and 2011 all bird nests in nestboxes were visited 2 3 times per week and the progress of breeding recorded. Predation by edible dormice was noted where the evidence indicated this. Eggs, recently hatched, fledged and adult birds were predated. Predation of the first clutch was greater when dormice emerged earlier from hibernation rather than later (60% vs. 25 %). Predation levels by dormice on later clutches were constant across years (c. 50 %) although the number of nesting attempts was always much lower than the first clutch. Keywords: nest losses, nest failure, great tit, blue tit 1. Introduction The edible or fat dormouse (Glis glis) is a nocturnal arboreal rodent with a principally mainland Europe range (Kryštufek 2010). This hibernating species was released in southern England in 1902 and has spread through much of an area defined and characterised by the broadleaved woodlands of the Chilterns and motorways (Thompson 1953, Morris 1997). A long-term population study has followed the numbers in a wood in the Chilterns, England using monthly inspections of specially made edible dormouse nestboxes attached to trees (Morris & Morris 2010). From a few individuals per year found in nestboxes in the mid-1990s the population has grown almost exponentially in recent years to hundreds of animals found in each summer inspection. The edible dormouse is predominantly vegetarian, particularly consuming beech mast, fleshy fruits, nuts (acorns and hazelnuts), buds, leaves and flowers of trees, arthropods, fungi and mosses (Vietinghoff-Riesch 1960). In England, they are recorded as causing significant levels of damage to the bark of forest trees in plantations (Platt & Rowe 1964, Jackson 1994). Invertebrates (slugs, caterpillars, aphids, myriapods and beetles) are only a supplementary diet and predation on vertebrates was thought exceptional by Holišová (1968). Other published work from Europe has shown that the edible dormouse regularly predates nests of birds (Vietinghoff-Riesch 1960, Juškaitis 2006, Adamík & Král 2008a). The edible dormouse competes for nestboxes with hole-nesting birds and may consume eggs and kill and eat both nestlings and incubating or brooding parents. These can include rare as well as more common species, though all birds are protected by law whilst nesting. In the past, woodland hole-nesting birds and the edible dormouse had a distinct sequential pattern of cavity use. However, in the last decades the changing climate in Central Europe may have created unequal advances in phenology; the edible dormouse has apparently advanced its emergence

2 210 Roger Trout et al. from hibernation faster than woodland birds (Koppmann-Rumpf et al. 2003). The population size of edible dormice is also positively correlated with the number of predated nests (Juškaitis 2006, Adamík & Král 2008b). This paper presents data for on predation by edible dormice of woodland birds nesting in the dormouse nestboxes on our UK study site. 2. Material and methods The nestbox monitoring scheme used by Morris & Morris (2010) with 145 boxes was supplemented by an extra 75 boxes erected during 2008 and During spring 2009, 2010 and 2011 all nestboxes were inspected twice a week from late April until early July. Inspection involved use of a flexible endoscope inserted into the nestbox entrance hole, since this created little disturbance to birds or dormice inside. For those boxes with evidence of birds nesting, each visit recorded the progress of nestbuilding, the bird species involved, presence of eggs, sitting adult bird, nestlings or fledgling young. A small number of late nesting attempts commenced either when the majority of early nests had either feathered young or else began in the same nestbox after young had flown; these were termed late clutches. Successful fledging and any reasons for failure (including abandonment, broken eggs, pieces of bird, presence of edible dormouse or their signs droppings, hair, major nest disturbance, green leaves brought in) were recorded by inspection of the interior of the nestbox. Only those with evidence of edible dormouse activity were recorded as edible dormouse predation. Instances of abandoned (undisturbed) nests with dead young could not be allocated to edible dormouse predation of adults away from the nest or other causes of adult desertion and were recorded separately. 3. Results Nests were principally of great tit (Parus major) [138] and blue tit (Cyanistes caeruleus) [32] and all analyses relate to these species. The number of nesting attempts recorded differed in the 3 years. Not all 178 nests completed resulted in active bird breeding. The commencement date of egg laying also differed, with 2009 being the earliest. In each year some birds fledged successfully and some were predated often by edible dormice. The pattern of bird nesting and predation by edible dormice is shown in Table 1 for the first clutch nests and Table 2 for the later clutch nests. Great tits predominated in the nestboxes, both for the first and late clutches. Successful first nesting varied across years from %, whilst the recorded level of nest predation showing evidence that it was edible dormouse was respectively %. Edible dormice ate eggs, recently hatched and growing juveniles, almost fledged young and even adult birds of both species in the boxes. On one occasion an adult female great tit with brood patch was found on the ground below a disturbed nestbox with predated young. She had a single bite right through the skull dorso-ventrally with both puncture wounds of a size fitting edible dormouse incisor teeth. Had this been a weasel or hawk attack (apart from a different wound pattern), the predator would have descended to ground and retrieved it, whereas edible dormice would not. The level of predation of later/second nests was similar across years at c. 50 %. One predation event could not be attributed with absolute certainty to edible dormouse, so both included and excluded assessments are shown. Overall, the proportion of predation by the edible dormouse for the two tit species was the same (33 % vs. 34 %). The timing of the main predation events differed between years by approximately one month

3 Predation by the edible dormouse (Glis glis) 211 mid May to mid June as shown in Table 1. This reflected an apparently major difference in emergence date (as represented by the numbers of edible dormice in nestboxes on the first Sunday of the month and mid month) between years (Tab. 3). Edible dormouse emergence was recorded earlier in 2009 and in larger numbers than other years, as represented by the two weekly nestbox checks of edible dormouse presence. Tab. 1 Fate of first clutch woodland birds nesting in 220 Glis nestboxes. First breeding attempt Completed nests Bird species Great tit 14 [67%] 41 [68%] 50 [77%] Blue tit 7 [33%] 11 [18%] 15 [23%] Others/unrecorded 0 [0%] 8 [13%] 0 [0%] Fate of nests/young Successful fledging 7 [33%] 32 [53%] 35 [54%] Dead/abandoned/unknown/ other predator 1 [5%] 9 [14%] 14 [21%] Predated by edible dormouse 13 [62%] 19 [32%] 16 [25%] Date of first multiple edible dormouse predation events 11 May 12 June 24 May Tab. 2 Fate of late clutch woodland birds nesting in Glis nestboxes. Later breeding attempt Completed nests Bird species Great tit 15 [83%] 6 [75%] 6 [100%] Blue tit 3 [17%] 2 [25%] 0 [0%] Fate of nests/young Successful fledging 4 [22%] 4 [50%] 2 [33%] Dead/abandoned/unknown/ other predator 6 [33%] 0-1 [0-12%] 1 [17%] Predated by edible dormouse 8 [45%] 3-4 [38-50%] 3 [50%] Tab. 3 Recorded total numbers of edible dormice in 220 nestboxes Nestboxes with edible dormouse 2009 good tree masting 2010 little tree masting 2011 very heavy tree masting First Sunday in May Third Sunday in May First Sunday in June Third Sunday in June

4 212 Roger Trout et al. 4. Discussion Edible dormice emerging from hibernation have lost much of their body weight and are very motivated to feed up both to regain body condition and to achieve breeding condition as soon as possible. During the night, when dormice are active, it was not surprising that all stages of bird breeding were attacked since those birds are diurnal and they would be asleep (Juškaitis 2006). The tits of either species are unable to defend themselves since they are very much smaller in body mass than edible dormice (11 20 g vs g). This was indicated by the similar proportion of predation events for the two tit species. Individual edible dormice on this site use the same nest box (or a very few adjacent ones) regularly during their whole lifetime up to 10 years (Morris & Morris 2010) although they do not always use nestboxes every day but may also use tree holes (Brooks & Trout 2012). The year 2009, with an earlier emergence from hibernation as defined by the population monitoring data, resulted in a much larger percentage loss of nests than occurred in the two years with later emergence. All bird nesting and predation events were prior to any breeding of the dormice. We have insufficient evidence to demonstrate whether good tree flowering years (2009 and 2011) result in less predation. The data from our study indicate a % loss of active nests of two common woodland bird species due to edible dormouse. Whilst it can be reasonably assumed that this figure may be appropriate to all woodland birds that breed in tree cavities (and possibly roosting bats) that edible dormouse can enter, it is not suggested that this level of loss would necessarily apply to all bird species breeding in the wood. This is firstly because it is well known that other predators such as corvids predate open-nesting species and secondly because we have no empirical measure of edible dormice taking those species. However, as the principle microhabitat where hungry edible dormice in spring/early summer are urgently seeking food at night is among the flowering and shooting branches of trees, they may well move along branches containing open-nesting bird species. There are other much rarer woodland species that nest in holes, e.g. spotted flycatcher (Muscicapa striata), nuthatch (Sitta europaea), tree creeper (Certhia familiaris), lesser and greater spotted woodpecker (Dendrocopos minor, D. major) (Adamík & Král 2008a). We are aware of two probable edible dormouse predation events involving the last species in our study site and also found an edible dormouse in a nestbox two days after finding a woodpecker there. As Koppmann-Rumpf et al. (2003) showed in their collation of 30 years data, the climate change advance in phenology has been much greater for edible dormouse (c. 1 month in 30 years) than for the woodland birds (c. 1 week in 30 years) and Adamík & Král (2008b) found a similar trend. Thus the implications of further climate change advancing the awakening date for edible dormouse is not a good omen for hole-nesting woodland birds living within the UK range of this non-native species. The UK government has a formal target to stop the decline in woodland birds and thus in the Chilterns area, where edible dormouse are present, this target (whether for the common but especially the rarer species) is apparently under significant threat. Edible dormice also are implicated in predation and disturbance in nest boxes of protected bat species (Grimsey, pers. comm.) and the protected native hazel dormouse (Muscardinus avellanarius) (Bakó & Hecker 2006, Juškaitis & Büchner 2010, Grimsey, pers. comm.), though no formal data has yet been gathered or published in the UK. This is in addition to the significant impact on some plantation trees by bark stripping (Koenig 1960, Platt & Rowe 1964, Jackson 1994) and the damage to and nuisance in houses and other human infrastructure (Morris 2009) caused by this non-native species. The level of

5 Predation by the edible dormouse (Glis glis) 213 bird predation found in this study is a further indication that work to prepare for local edible dormouse population management, including the prevention of the establishment of new UK populations, should be seriously addressed. 5. Acknowledgements We gratefully acknowledge the field assistance of Danielle Rozyska, Jasmine Lim, Brian Barton, Margaret and Peter Grimsey. Access to the site was by permission of the Royal Forestry Society. RT was funded by the Forestry Commission until March References Adamík, P. & Král, M. (2008a): Nest losses of cavity nesting birds caused by dormice (Gliridae, Rodentia). Acta Theriologica 53: Adamík, P. & Král, M. (2008b): Climate- and resource-driven long-term changes in dormice populations negatively affect hole-nesting songbirds. Journal of Zoology, London 275: Bakó, B. & Hecker, K. (2006): Factors determining the distribution of coexisting dormouse species (Gliridae, Rodentia). Polish Journal of Ecology 54: Brooks, S. & Trout, R. (2012): A trial of one-way entrance multi-capture traps and different attractants to capture the Edible dormouse (Glis glis) in England. Peckiana 8: Holišová, V. (1968): Notes on the food of edible dormice (Gliridae). Zoologické Listy 17: Jackson, J. E. (1994): The edible or fat dormouse (Glis glis) in Britain. Quarterly Journal of Forestry 88: Juškaitis, R. (2006): Interactions between dormice (Gliridae) and hole-nesting birds in nestboxes. Folia Zoologica 55: Juškaitis, R & Büchner, S. (2010). Die Haselmaus. Die Neue Brehm-Bücherei, Band 670, Westarp Wissenschaften, Hohenwarsleben :181 pp. Koenig, L. (1960): Das Aktionssystem des Siebenschläfers. Zeitschrift für Tierpsychologie 17: Koppmann-Rumpf, B., Heberer, C. & Schmidt, K. H. (2003): Long term study of the reaction of the edible dormouse Glis glis (Rodentia: Gliridae) to climatic changes and its interactions with holebreeding passerines. Acta Zoologica Academiae Scientarum Hungaricae 49 (Suppl. 1): Kryštufek, B. (2010): Glis glis (Rodentia: Gliridae). Mammalian Species 42 (865): Morris, P. A. (1997): The Edible dormouse. Mammal Society, London: 24 pp. Morris, P. A. (2009): Genus Glis: Edible dormouse (Glis glis). In: Harris, S. & D. Yalden (eds): Mammals of the British Isles: Handbook. 4 th Edition. Mammal Society, London: Morris, P. A. & Morris, M. (2010): A 13-year population study of the edible dormouse (Glis glis) in Britain. Acta Theriologica 55: Platt, F. B. W. & Rowe, J. J. (1964): Damage by the edible dormouse (Glis glis) in Wendover forest (Chilterns). Quarterly Journal of Forestry 58: Thompson H. H. (1953): The edible dormouse in England, Proceedings of the Zoological Society of London 122: Vietinghoff-Riesch, A. Frhr. von (1960): Der Siebenschläfer (Glis glis L.). Monographien der Wildsäugetiere Volume 14, Gustav Fischer Verlag, Jena: 196 pp.

6 214 Roger Trout et al. Accepted 13 June 2012 Authors addresses: Roger Trout* Rabbitwise-Plus consultancy, Holtside Batts Corner, Dockenfield Farnham, Surrey GU10 4EX, UK Emma Mayo, Sebastian Perceau-Wells, Sarah Brooks Imperial College field Station, Silwood Park Ascot, Berkshire SL5 7PY, UK *Corresponding author: Roger Trout (