Jared Verner

A comparison of the breeding ecology of birds nesting in boxes and tree cavities

ABSTI~ICT.-We compared laying date, nesting success, clutch size, and productivity of four bird species that nest in boxes and tree cavities to examine whether data from nest boxes are comparable with data from tree cavities. Western Bluebirds (Sinlin nrexicnnn) gained the mast advantage from nesting in boxes. They initiated egg laying earlier, had higher nesting success, lower predation rates, and fledged marginally more young in boxes than in cavities but did not have laracr clutches or hatch more eggs. Plain Titmice (Pnnis iriorrmtrrs) nesting earlier in boxes. ~oise Wrens (~roglo&tes ~eiion) nesting in boxes laid larger clutches, hatched more eggs, and fledged mare young and had marginally higher nesting success and lower predation rates. Ash-throated Flycatchers (Myinrclirrs cincmscens) experienced no apparent benefits from ncsting in bows versus cavities. No significant relationships were found between clutch size and bottom area or volume of cavities for any of these species. These results suggest that researchers should use caution when extrapolating results from nestbox studies of reproductive success, predation rates, and productivity of cavity-nesting birds. Given the different responses of these four species to nesting in boxes, the effects of the addition of nest boxes on community structure also should be considered. Rrcrived 19 September 1996, nccepted 21 April 1997. NEST BOXES MAY BE USED AS A CONSERVATION

Foraging habitat and home-range characteristics of California spotted owls in the Sierra Nevada

We examined habitat use patterns at two spatial scales among six radio-tagged California Spotted Owls (Strix occidentalis occidentalis) in the Sierra Nevada. Foraging owls selected macrohabitats composed of larger trees (> 52 cm dbh) with canopy closures of 40% and greater. Owls used forests composed of medium trees (28-52 cm dbh) and habitats with less than 40% canopy closure, which is less frequently than expected. Fewer than 2% of telemetry locations occurred in clearcut/shrub/plantation habitat which represented 30% of available habitat. Foraging owls used microhabitats that were characterized by multiple vegetative strata, large tree size classes, high tree basal areas and woody debris. The median 100% minimum convex polygon home-range was 1,439 ha (n = 5, June to December, 1987). Telemetry locations were statistically independent when separated by five days. Estimates of minimum convex polygon and modified minimum convex polygon size based on statistically independent telemetry data were significantly smaller than estimates based on continuous and single-observation monitoring.

Fluctuating populations of house wrens and Bewick's wrens in foothills of the Western Sierra Nevada of California

In foothills of the western Sierra Nevada, 31 km east of Madera, California, we studied whether Bewicks Wrens (Thryomanes bewickii) tend to be excluded from an area occupied by House Wrens (Troglodytes aedon) as reported in several studies in the eastern United States. Neither point counts from 1985 to 1997 nor spot mapping from 1989 to 1993 suggests any interaction between these species. The study period included the most prolonged drought and the most severe period of winter weather in the 64-year climatological record from the study site. House Wren abundance was significantly related to the 4-year running average of annual precipitation and to the lowest temperature recorded in the winter months preceding survey counts. We speculate that House Wrens cannot maintain their numbers by local recruitment during droughts in the oak-pine woodlands that dominate our study area and that recovery of their population following droughts involves recruitment from other areas, probably riparian zones and other mesic habitats elsewhere in the Sierra foothills and Central Valley of California. There was no influence of precipitation on abundance of Bewicks Wrens and, although they apparently sustained heavy mortality during a period of extreme winter weather, their numbers otherwise were not related to the lowest temperature during the winter preceding counts.

RETURN RATES OF BANDED GRANIVORES IN RELATION TO BAND COLOR AND NUMBER OF BANDS WORN

Abstract We tested the null hypotheses of (1) no effect of band color and (2) no effect of number of bands worn on annual recapture rates of birds on their winter range. Results are reported from four species of granivores—Spotted Towhee (Pipilo maculatus), Golden-crowned Sparrow (Zonotrichia atricapilla), White-crowned Sparrow (Z. leucophrys), and Dark-eyed Junco (Junco hyemalis). We found no effect of the number of bands worn on return rates of these species, nor did we detect an effect of band color on return rates. In the latter case, however, the power of our tests was low, and some results hinted at possible effects of color, especially yellow bands on Golden-crowned Sparrows.

Ecological Community Structure Analyses in the Formulation, Implementation, and Enforcement of Law and Policy

Abstract Most of what is currently known about ecosystems derives from two sources: comprehensive studies by classical ecologists and economically motivated studies by resource specialists. The former have traditionally concentrated on natural or long-undisturbed ecosystems, the latter on those few species in managed or polluted ecosystems that are harvested, hunted, or fished. A recent genre of legislation, drafted with insight provided by the scientific community, recognizes the dearth of ecological information on managed or polluted communities (which are becoming far more ubiquitous and important) and dramatically raises the requirements for comprehensive data and data analyses to guide managerial and pollution abatement policies. This paper describes several important current efforts to use ecological community structure analyses to implement and enforce such legislation and some effects of such analyses on environmental policy.