. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 170 CALIFORNIA FISH AND CAME varied seasonally. The appearance of earthworms in the diet during the winter may have been a result of high water levels washing the worms out of the soil. A similar occurrence involving terrestrial arthropods was mentioned by Hynes (1950). Seasonal variation in the diet is a reflection of changes in the actual numbers of food items as well as changes in their relative availability. My results and those o
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 170 CALIFORNIA FISH AND CAME varied seasonally. The appearance of earthworms in the diet during the winter may have been a result of high water levels washing the worms out of the soil. A similar occurrence involving terrestrial arthropods was mentioned by Hynes (1950). Seasonal variation in the diet is a reflection of changes in the actual numbers of food items as well as changes in their relative availability. My results and those of others (Semler 1971, Kynard 1978) indicate that egg predation is more common among male sticklebacks than among females. Breeding males may consume eggs obtained in successful raiding attempts, and there is evidence that males may eat some of their own brood (Rohwer 1978). Other instances of egg predation are probably due to attacks on nests by schools of females and nonbreeding males. These raider packs have been observed to destroy nests and to eat the eggs (Kynard 1978). 0) o 3 o o O 70- 60' 50' 40' 30' 2 0' 10- I ± ± ± Insects Earthworms A. A .A —^ A -A A-- T ' 1 ' i ' 1 • 1 ' 1 r— Feb Apr Jun Aug Oct Dec Month! FICURE 1. Seasonal variation in the consumption of major food groups by threespine stickleback from San Pablo Creek, Contra Costa County, California. The correlation between food supply and frequency of nest raiding (Adal- steinsson 1979) may be due to increased attacks by raider packs when food is scarce. It is likely that the purpose of these attacks is to obtain food and their frequency would be influenced greatly by food supply. In contrast, nest raiding in breeding males is closely linked to the reproductive process, and therefore not affected by supply of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfect
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