Competition and patterns of resource use by two sympatric raptors

Article Abstract:

Few raptors are subjected to predation or other interference that would reduce the population to below the limits imposed by food supply. Some researchers suggest that declining food resources may cause concurring species of raptors to compete for food, while others suggest that behavioral factors are more inclined to reduce competition for food. A new study examines the two opposing ideas by studying the food habits of Swainson's and Harris' Hawks during a period of prey decline. It is shown that direct competition for food did not occur between the two species because it was mediated by aggressive behavior.

Behavior, Birds of prey, Raptors (Birds), Hawks, Competition (Biology)

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Temporal-spatial patterns of food caching in two sympatric shrike species

Article Abstract:

Temporal changes in food caching and cache use by shrikes relies on prey availability and energy requirements. The air temperature influences food preservation and storage time period, while he storing of detestable prey affects cache use. Kleptoparasitism on caches is seemingly low. The spatial distribution of caches is influenced by the availability of suitable shrubs, the distribution of cached prey, the distance to the nest, and the hiding of stored food within the shrub.

Food, Protection and preservation, Food preservation, Shrikes

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Effects of caching on acorn tannin levels and blue jay dietary performance

Article Abstract:

Acorns cached in the field were subjected to changes in tannin levels during winter storage and exposed to ambient conditions. Tannin activity on the acorns from two oak species differed significantly. Tannin levels in experimental caches were higher compared to acorns in cold storage. Thus, poor diet of cached or uncached, and both low and high tannin species of acorn were observed on the birds.

Oak, Oaks, Tannins, Acorns, Blue jay

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