Kristine L. Preston

Modeling ecological minimum requirements for distribution of greater sage‐grouse leks: implications for population connectivity across their western range, U.S.A

Greater sage-grouse Centrocercus urophasianus (Bonaparte) currently occupy approximately half of their historical distribution across western North America. Sage-grouse are a candidate for endangered species listing due to habitat and population fragmentation coupled with inadequate regulation to control development in critical areas. Conservation planning would benefit from accurate maps delineating required habitats and movement corridors. However, developing a species distribution model that incorporates the diversity of habitats used by sage-grouse across their widespread distribution has statistical and logistical challenges. We first identified the ecological minimums limiting sage-grouse, mapped similarity to the multivariate set of minimums, and delineated connectivity across a 920,000 km2 region. We partitioned a Mahalanobis D2 model of habitat use into k separate additive components each representing independent combinations of species–habitat relationships to identify the ecological minimums required by sage-grouse. We constructed the model from abiotic, land cover, and anthropogenic variables measured at leks (breeding) and surrounding areas within 5 km. We evaluated model partitions using a random subset of leks and historic locations and selected D2 (k = 10) for mapping a habitat similarity index (HSI). Finally, we delineated connectivity by converting the mapped HSI to a resistance surface. Sage-grouse required sagebrush-dominated landscapes containing minimal levels of human land use. Sage-grouse used relatively arid regions characterized by shallow slopes, even terrain, and low amounts of forest, grassland, and agriculture in the surrounding landscape. Most populations were interconnected although several outlying populations were isolated because of distance or lack of habitat corridors for exchange. Land management agencies currently are revising land-use plans and designating critical habitat to conserve sage-grouse and avoid endangered species listing. Our results identifying attributes important for delineating habitats or modeling connectivity will facilitate conservation and management of landscapes important for supporting current and future sage-grouse populations.

INDEPENDENT EFFECTS OF FOOD AND PREDATOR-MEDIATED PROCESSES ON ANNUAL FECUNDITY IN A SONGBIRD

We investigated the relative importance and interaction of ecological processes affecting annual fecundity in birds by simultaneously manipulating food availability and nest predation risk in a small songbird, the Wrentit (Chamaea fasciata). From 2000 to 2002 we provided supplemental food to individual Wrentit territories, and during 2002 we altered nest predation risk by providing supplemental food to their principal predators, Western Scrub-Jays (Aphelocoma californica). These experiments were conducted during a period of high interannual variation in rainfall, with 2002 being one of the driest years on record. Food-supplemented Wrentits in a normal predation environment produced an average of 0.54 more fledglings per year than control pairs over the three breeding seasons. During the feeding plus predation manipulation experiment, Wrentit food supplementation and lowered nest predation risk each independently increased the probability that a Wrentit pair would fledge young; however, the interaction between food supplementation and altered nest predation risk was not significant. Thus, even in an extreme drought year, both food and nest predation had equal but independent effects on reproductive success and annual fecundity. Combining supplemental food with reduced nest predation did not result in a synergistic increase in annual fecundity, primarily because Wrentits did not produce multiple broods. Our results suggest that whether food and predation have additive or synergistic effects on reproductive success depends on the life history of the species and the environment in which they live.

THE ROLE OF FOOD, NEST PREDATION, AND CLIMATE IN TIMING OF WRENTIT REPRODUCTIVE ACTIVITIES

Abstract ABSTRACT Timing of breeding activities by birds hasimportant fitness consequences, as deciding when tonest can affect nest success. For three breedingseasons, we provided supplemental food to Wrentits(Chamaeafasciata) inhabitingsemiarid shrublands. We tested the effects of foodsupplementation on timing of initial egg laying,number of nests attempted, timing of fledging, andlength of the breeding season. We also evaluatedwhether Wrentits timed nest initiation to avoidperiods of greatest predation risk. Our study wasconducted during a period of high interannualvariation in precipitation. Supplemental food didnot advance laying date in Wrentits. During adrought, even Wrentits given supplemental fooddelayed nesting, initiated fewer nesting attempts,fledged young earlier, and reduced the length ofthe breeding season. In a year of average rainfall,supplemental food allowed pairs to continuerenesting late into the summer, after repeated nestlosses from predation. Wrentits did not timenesting to avoid periods of greatest predationrisk. In timing initial breeding, Wrentits appearedto be responding to climatic conditions and toindirect cues that predicted environmentalconditions later in the breeding season rather thanto food availability at the time of egg laying.