Dietary relationships among shrumsteppe passerine birds: competition or opportunism in a variable environment

Journal Article · Sat Mar 01 04:00:00 EST 1980 · Ecol. Monogr.; (United States)

DOI:https://doi.org/10.2307/2937248· OSTI ID:5101418

Rotenberry, J T

The suggestion that in less stable environments resource limitation and subsequent interspecific competition may be relatively unimportant in determining bird community structure is explored by examining the dietary relationships within a guild of three ground-foraging passerine birds (Horned Lark, Sage Sparrow, and Western Meadowlark) in the shrubsteppe of southeastern Washington, USA, an area of severe, arid, unstable climate. General dietary analyses indicated a strong temporal component to the organization of bird diets: different species collected at the same time ate much the same things while the same species collected at different times ate different things. This pattern is reinforced by cluster analysis and stepwise discriminant analysis. Similarities in diet extended to other components as well. Dietary diversities tended to be the same for contemporaneous collections of birds, as did averge prey sizes, although the latter evidenced a few statistically significant exceptions. Theoretically predicted relationships between diet and trophic structure morphology emerged only at the most general level, and even then were not always observed. In general, differences in body size or bill length were insufficient to account for variations in prey sizes, although meadowlarks did on occasion take significantly larger items than the other, smaller species. Average prey size was significantly correlated with the proportion of seeds in the diet and varied seasonally as seed consumption varied. Several aspects of this study indicate that shrubsteppe passerines are largely opportunistic in their foraging and diet selection, and that the apparent absence of fine tuning to their competitive milieu is most likely a function of the variable environment in which they coexist.

• Research Organization: Oregon State Univ., Corvallis
• OSTI ID: 5101418
• Journal Information: Ecol. Monogr.; (United States), Journal Name: Ecol. Monogr.; (United States) Vol. 50:1; ISSN ECMOA
• Country of Publication: United States
• Language: English

Related Subjects

510100 -- Environment
Terrestrial-- Basic Studies-- (-1989)
54 ENVIRONMENTAL SCIENCES
550100* -- Behavioral Biology
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
BEHAVIOR
BIOLOGICAL VARIABILITY
BIRDS
COMPETITION
DIET
FOOD CHAINS
POPULATION DYNAMICS
PREDATOR-PREY INTERACTIONS
SEEDS
VERTEBRATES