DISTRIBUTION AND ABUNDANCE 87 



of the pattern of life of the aniinaL Although, therefore, most of the 

 information about predators of frogs is anecdotal, it is likely that the 

 list of predators given by Smith (195 1) — hawks, owls, crows, gulls, 

 ducks, terns, herons, hedgehogs, stoats, weasels, badgers, otters, rats, 

 and snakes — is a fair indication that many animals will eat the frog if 

 they can fmd it. It is, however, very difficult to come to any quantita- 

 tive conclusions on the available information, for tliis is scattered 

 through the hterature on other animals, often in the form of casual 

 comments not indexed by abstractors. If one considers the size of most 

 of the animals in the above hst, and the density of the frog population, 

 say five frogs to the acre, it seems unlikely that any except the last 

 can be dependent on the frog as a source of food. Probably they use 

 frogs at certain times of the year, and feast for a few days, but, at 

 other times, chance on frogs by luck, and then add an inconsiderable 

 item to their diet. It is therefore difficult to beheve in any reciprocal 

 predator-prey relation. More probably, these animals act as catas- 

 trophic agents, and they may be important in this way. One in 

 particular deserves special attention. 



I have known some of the ponds in my area for at least forty years. 

 I have never considered that the mallard duck [Anas platyrhyticlws) was 

 typically a bird of the small ponds used by frogs. It occurred on some 

 of the larger ponds, and on my nightly rounds in the thirties, I dis- 

 turbed a pair, not always on the same pond, but never on more than 

 one, so that I concluded that it was the same pair, and the only one in 

 about a square mile. In 1958, the frog population was less than I have 

 ever known it, and I found the mallard on many remarkably small 

 ponds. Two of these had two pairs, and the vegetation was obviously 

 chewed to an extent suggesting pressure on the food supply. It was 

 difficult to beheve that either frogs or tadpoles could survive in these 

 ponds. If the birds visit other ponds in the neighbourhood in turn, as I 

 beheve they do, dien the shortage of frogs would be easily explamed 

 by the increase in the population of ducks, but whether this is really the 

 explanation is uncertain. 



Another predator that may sometimes be important is the moorhen, 

 Gallinula chloropus. As I pointed out in Chapter i, this bird occasionally 

 eats spawn, but is erratic in tliis behaviour. Bendey Heath Church 

 Pond almost always has a pair of these birds, and generally has spawn 

 as well. I never know whether the birds are going to attack the spawn 

 or leave it entirely alone. When they do eat it, they leave litde or 



