SIZE OF MARSH FROGS IN THE DIET OF EURASIAN OTTER IN SOUTHERN BULGARIA

Our study was carried out in the south of Bulgaria, providing original data on the size of the marsh frog Pelophylax ridibundus (Pallas, 1771) in otter Lutra lutra (Lin- naeus, 1758) diet. A method was devised for estimating the size of these anurans found as bone remains in otter spraints. A very strong positive correlation between the ileum's max- imum width and frogs' standard body length was highlighted. The linear regression equa- tion was: standard body length = 10.4 + 14.1 × ileum's maximum width. The mean body length of marsh frogs in otter spraints was 53.49 mm. During the warm season otters fed on about four times more diverse sized anurans. The size group 41-60 mm always dominated in otter diet, particularly in the cold season. It could be concluded that in the study area otters fed predominantly on juvenile and sub-adult marsh frogs.

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