Notes
Collapsing Burrow Causes Death of a Eurasian Beaver, Castor fiber
LlATR.THOMSEN'. FJONA SHARPE2•and FRANK ROSELLJ [ Depanment or ZooJogy. University of Aarhus. Denmark
2School of Biology. University of SI Andrews. Fife. Scotland
JFaculty of Ans and Sciences. Department of Environmental and Heallh Studies. Telemark Universiry College. N-3800 Bø i Telemark. Norway
Thomsen. Liat R.. Fiona Sharpe. and Frank RoseIl. 2004. Collapsing burrow causes death of a Eurasian Beaver.Caslor fiber.Canadian Field-Naturalisl I18(3): 434-435.
The death of a Eurasian BeaverCaslOr fibercaused by a collapsing burrow in southeasl Norway is reported.Twadays of heavy rainfall had presumably caused the burrow[Qcollapse. suffocating the animal.
Key WOlds: Beaver.CaSlOr fiber.collapsing burrow. southeasr Norway.
SeveraI causes of death have been reponed for Eurasian Beavers (Castor fiber) (RoselJ et al. 1996;
Nolet et al. 1997). bUl to aur knowledge [his is Lhe firsl repon of a beaver k.iJled due LO a colJapsing bur- row. The beaver was an aduh solirary male (21.5 kg and 5 years old: age was determined by examining annuaJ cementum and dentine layers of the first molar (van Nostrand and Stephenson 1964)). His mate died two months earlier. probably due to old age (18 years old). The animal was one of severaJ radio tagged beavers that were followed during a lield study in spring and summer 2000 in Telemark Counry. south- eas! Norway (59°25"N. 09°03'0 (see Campbell 2000).
On the evening of14July 2000 it was noted thar the puJse interval of the radio signal had increased. The signal is inversely related to !he body temperature of the animal (Alterra 1999), thus a higher pulse inlerval indicated that the beaver had died. The dead beaver was located in the main part of a paJ11y coJlapsed bur- row (assessed to be relatively new), which was eXC3- vated four days later in order to lind and retrieve the carcass (Figure' I).
Beavers dig burrows wJ1ere banks are sufficiently high (Wilsson 1971; Zurowsk.i 1992). A burrow usu- ally consists of a single living chamber, a water basin, and a tunnel with exit below the water level (Wilsson 1971). The beaver was Iying in the chamber (I m long and 70 cm wide) of the collapsed burrow, facing to- wards the exit. The chamber was siruated 210 cm from the water's edge, 80 cm below the surface of the riverbank, and6Qcm above the current water leve!.
Apparently the ceiling of the chamber had collapsed on top of the beaver causing the death of the animal, presumably by suffocation. There was loose sand aloog the flanks of and undemeath the body of the dead beaver. The last 10 cm of"the beaver's tai! was bent downwards into the sand and the right hind foot was crouched as if the beaver had been attempting to dig with it. The beaver had no extemal injuries and seemed to be in good condition.
FIGUREI.The dead solir.ary adult beaver localed in the chamber of a partly collapsed burrow.
The burrow was dug in sand y soil. In the week prior tothe discovery of the beaver there had been twa days with heavy rainfaJl in the area with 30.8 mm and 24.6 mm of rain, respectively (data from the Norwegian Meteorologicallostirute).
We conclude that the combi.nation of heavy rallfall and a sandy soil had caused the burrow to collapse, therefore causing the death of the beaver. How preva- lent this cause of death is in beavers is unknown. How- ever, we expect that more tie1d studies using radio telemetry, in areas wbere beavers dig burrows, could clarify this issue.
434
Acknowledgments
We thank Frode Bergan for help with excavating the beaver and Inger Hanssen-Bauer for providing the we:Jther data. The study was nnancially supported by Telem:Jrk L'niversiry College. The experimentscomply with the current Norwegian /aw, the country in which they were perfonned.
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ReceiveLi26November2002 Accepled I November2004
