. The Canadian field-naturalist. 60 The Canadian FieldtNaturalist [Vol. XXXIX The average length of the drain of 21 hiberna- tion dens measured was 3 feet 5 inches, the short- est 7 inches and the longest 7 feet 9 inches. The average depth from the surface of the ground to the deepest point of the drain of 24 dens measured was 4 feet 1 inch. The deepest drain was 5 feet 6 inches and the shallowest, 2 feet 4 inches. In this latter case, the den was on thin soil, only 35 inches to rock. The diameter of the burrow was inches to expansions of 5, 7, and 9 inches. Another function for the drain,
. The Canadian field-naturalist. 60 The Canadian FieldtNaturalist [Vol. XXXIX The average length of the drain of 21 hiberna- tion dens measured was 3 feet 5 inches, the short- est 7 inches and the longest 7 feet 9 inches. The average depth from the surface of the ground to the deepest point of the drain of 24 dens measured was 4 feet 1 inch. The deepest drain was 5 feet 6 inches and the shallowest, 2 feet 4 inches. In this latter case, the den was on thin soil, only 35 inches to rock. The diameter of the burrow was inches to expansions of 5, 7, and 9 inches. Another function for the drain, aside from the protection afforded against moisture, is in the use to which it is sometimes put as a place into which the dirt from the exit shaft is packed. Frequently we find this earth in the drain after the squirrel has opened his den. It is also found in the bottom of the exit shaft. The Closing-in Plug.—By the closing-in plug we mean a plug of earth several inches long placed in the burrow leading to the outside at the time of going into aestivation. The plug is made of earth probably taken from the drain and tamped firmly into place by the squirrel, using his nose in the operation. When ready for aestivation the squirrel closed its den against all intruders found inhabiting its summer den during the winter, such as crickets, spiders, salamanders, toads, pocket gophers and cottontails. This is done with the closing-in plug and must of necessity be done from the in- side of the hibernation den, as a last act. This plug was first noted in the closed hibernation den, as in Fig. 7. It was noticed then that it was made of new dry earth, of late summer, the nose 6URFACE OF Gt^OUND. DRAIN 3^ J^LALLP hlBERMATlOM DE.^ ( COLUMe>i/KhUS) Figure 8.—A CLOSED HIBERNATION DEN. This is the den shown in photograph in Figure 9, showing the relative depths of the cell and drain. (Original).. Please note that these images are extracted from scanned page images that may have b
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