Plant and animal species have been used for decades as indicators of air and water quality and agricultural and range conditions. Increasingly, vertebrates are used to assess population trends and habitat quality for other species. In this paper we review the conceptual bases, assumptions, and published guidelines for selection and use of vertebrates as ecological indicators. We conclude that an absence of precise definitions and procedures, confounded criteria used to select species, and discordance with ecological literature severely weaken the effectiveness and credibility of using vertebrates as ecological indicators. In many cases the use of ecological indicator species is inappropriate, but when necessary, the following recommendations will make their use more rigorous: (1) clearly state assessment goals, (2) use indicators only when other assessment options are unavailable, (3) choose indicator species by explicitly defined criteria that are in accord with assessment goals, (4) include all species that fulfill stated selection criteria (5) know the biology of the indicator in detail, and treat the indicator as a formal estimator in conceptual and statistical models, (6) identify and define sources of subjectivity when selecting monitoring and intetpreting indicator species, (7) submit assessment design, methods of data collection and statistical analysis, interpretations, and recommendations to peer review and (8) direct research at developing an overall strategy for monitoring wildlife that accounts for natural variability in population attributes and incorporates concepts from landscape ecology.

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Regardless of sex ratio, a polygynous mating is expected to be adaptive for the females as well as for the male. Two possible selective bases for the evolution of polygyny are considered: 1) One male may make it advantageous to several females to mate with him by appropriating a large share of a limited number of nest sites. 2) When a large share of the food for the young is obtained from the territory, local variations in food availability could influence the mating system. Given a sufficient minimum level of food supply, the difference in food availability between two males' territories may be great enough to permit a female to rear more young on the better territory, unaided by her mate, than she could on the poorer one even with full assistance from her mate. In this case, selection would favor a female pairing with the male on the better territory, even if this meant establishing a polygynous association. Fourteen of 291 species of North American passerine birds have been reported to be regularly polygynous or promiscuous. Thirteen of the 14 breed in marshes, prairies, or savannah—like habitats, where productivity resulting from solar energy is concentrated into a narrow vertical belt; that in a forest is spread unevenly over a broad vertical belt. Thus, the density of productivity–and of avian food sources–is potentially much greater in marshes and prairies than in forests. Hence, marshes and prairies are more likely than forests to present the minimum requisite food supply and sufficiently great differences in available food between territories for selection to favor polygyny.

Brood—parasitic Brown—headed Cowbirds (Molothrus ater) in the eastern Sierra Nevada of California, breed and feed in almost totally disjunct areas that reflect local optima for finding host nests and food, respectively. Radio—tracking showed that five females and four of eight males spent mornings in host—rich habitats such as forests and then commuted 2.1—6.7 km to one or more prime feeding sites such as horse corrals and bird feeders for the rest of the day. The four noncommuting males, which were all yearlings and possibly socially subordinate, also showed high mobility bud did not occupy the same area each morning. Since cowbirds lay eggs in the morning and were rarely seen feeding then, the disjunct areas visited by commuters can be characterized as morning—breeding (egg—laying) and afternoon—feeding areas. We found little evidence of territoriality on morning ranges, nor did we find evidence of prolonged pair bonds. The morning ranges of commuters averaged 68 ha, and their total home ranges, including afternoon—feeding areas, averaged 442 ha. These are among the largest breeding home ranges described for passerines, and they equal those of certain raptors. Raptors require large areas to provide a sufficient prey base, and cowbirds require similarly large areas to provide a sufficient number of host nests. The cowbird's commuting pattern, which is unique among passerines, involves a shift from largely asocial behavior in the morning to extreme sociality in the afternoon. Unlike related nonparasitic icterids that disperse from central breeding sites to feed, cowbirds do the reverse, dispersing from centralized feeding sites to breed. The cummuting behavior of cowbirds is yet another example of the flexibility of a species' behavioral ecology in response to the dispersion of resources essential for maintenance and reproduction.

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