No abstract

Estimation of avian nest survival has traditionally involved simple measures of apparent nest survival or Mayfield constant‐nest‐survival models. However, these methods do not allow researchers to build models that rigorously assess the importance of a wide range of biological factors that affect nest survival. Models that incorporate greater detail, such as temporal variation in nest survival and covariates representative of individual nests represent a substantial improvement over traditional estimation methods. In an attempt to improve nest survival estimation procedures, we introduce the nest survival model now available in the program MARK and demonstrate its use on a nesting study of Mountain Plovers (Charadrius montanus Townsend) in Montana, USA. We modeled the daily survival of Mountain Plover nests as a function of the sex of the incubating adult, nest age, year, linear and quadratic time trends, and two weather covariates (maximum daily temperature and daily precipitation) during a six‐year study (1995–2000). We found no evidence for yearly differences or an effect of maximum daily temperature on the daily nest survival of Mountain Plovers. Survival rates of nests tended by female and male plovers differed (female rate = 0.33; male rate = 0.49). The estimate of the additive effect for males on nest survival rate was 0.37 (95% confidence limits were 0.03, 0.71) on a logit scale. Daily survival rates of nests increased with nest age; the estimate of daily nest‐age change in survival in the best model was 0.06 (95% confidence limits were 0.04, 0.09) on a logit scale. Daily precipitation decreased the probability that the nest would survive to the next day; the estimate of the additive effect of daily precipitation on the nest survival rate was −1.08 (95% confidence limits were −2.12, −0.13) on a logit scale. Our approach to modeling daily nest‐survival rates allowed several biological factors of interest to be easily included in nest survival models and allowed us to generate more biologically meaningful estimates of nest survival.

Estimation of avian nest survival has traditionally involved simple measures of apparent nest survival or Mayfield constant-nest-survival models. However, these methods do not allow researchers to build models that rigorously assess the importance of a wide range of biological factors that affect nest survival. Models that incorporate greater detail, such as temporal variation in nest survival and covariates representative of individual nests represent a substantial improvement over traditional estimation methods. In an attempt to improve nest survival estimation procedures, we introduce the nest survival model now available in the program MARK and demonstrate its use on a nesting study of Mountain Plovers (Charadrius montanus Townsend) in Montana, USA. We modeled the daily survival of Mountain Plover nests as a function of the sex of the incubating adult, nest age, year, linear and quadratic time trends, and two weather covariates (maximum daily temperature and daily precipitation) during a six-year study (1995)(1996)(1997)(1998)(1999)(2000). We found no evidence for yearly differences or an effect of maximum daily temperature on the daily nest survival of Mountain Plovers. Survival rates of nests tended by female and male plovers differed (female rate ϭ 0.33; male rate ϭ 0.49). The estimate of the additive effect for males on nest survival rate was 0.37 (95% confidence limits were 0.03, 0.71) on a logit scale. Daily survival rates of nests increased with nest age; the estimate of daily nest-age change in survival in the best model was 0.06 (95% confidence limits were 0.04, 0.09) on a logit scale. Daily precipitation decreased the probability that the nest would survive to the next day; the estimate of the additive effect of daily precipitation on the nest survival rate was Ϫ1.08 (95% confidence limits were Ϫ2.12, Ϫ0.13) on a logit scale. Our approach to modeling daily nest-survival rates allowed several biological factors of interest to be easily included in nest survival models and allowed us to generate more biologically meaningful estimates of nest survival.

Little question exists that the main bodies of North American prairie (i.e., the tall‐grass, mixed, and shortgrass) are among the most endangered resources on the continent. The purpose of this paper is to provide a past and present biological baseline by which to understand North American prairies and to provide a platform for future conservation. Events both immediate to the end of the Pleistocene and historic suggest that the present grassland conditions are different from those within which most of the grassland organisms evolved. Our analysis suggests that few grassland landscapes remain adequate in area and distribution to sustain diversity sufficient to include biota and ecological drivers native to the landscape. A robust and history‐based scenario to conserve Great Plains grasslands is to 1) identify areas large enough to sustain an ecological system with all its biodiversity, 2) reverse significant losses in area of native grasslands, 3) ensure that restoration matches the grassland previously existing at that site, 4) refocus the profession of range management, and 5) establish a more meaningful agency design for grassland and natural resource management.

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We used feathers of known origin collected from across the breeding range of a migratory shorebird to test the use of isotope tracers for assigning breeding origins. We analyzed deltaD, delta13C, and delta15N in feathers from 75 mountain plover (Charadrius montanus) chicks sampled in 2001 and from 119 chicks sampled in 2002. We estimated parameters for continuous-response inverse regression models and for discrete-response Bayesian probability models from data for each year independently. We evaluated model predictions with both the training data and by using the alternate year as an independent test dataset. Our results provide weak support for modeling latitude and isotope values as monotonic functions of one another, especially when data are pooled over known sources of variation such as sample year or location. We were unable to make even qualitative statements, such as north versus south, about the likely origin of birds using both deltaD and delta13C in inverse regression models; results were no better than random assignment. Probability models provided better results and a more natural framework for the problem. Correct assignment rates were highest when considering all three isotopes in the probability framework, but the use of even a single isotope was better than random assignment. The method appears relatively robust to temporal effects and is most sensitive to the isotope discrimination gradients over which samples are taken. We offer that the problem of using isotope tracers to infer geographic origin is best framed as one of assignment, rather than prediction.

No abstract

Conservation of riparian vegetation in westernNorth America ha~ in parg emphasized providing habitats for a locally diverse avifaunat Site diversity, especially reia. tire to the number of species preseng is generally high within riparian avifaunas. Between-habitat diversity changes across a watersheag with riparian species assemblages differ. ing most from upland assemblages at the highest and lowest elevation~ This pattern can be attributed to enhanced avian movements within the riparian vegetatiorL The corridors for bird movements, in turn, facilitate faunal mixing on a broader scal~ influencing regional diversity within land-scape~ Riparian ecosystems are viewed as connectors of forests across fragmented landscape~ In western setting& however, they are highly lineartzed forests transecting watersheds between upland associations of high elevations and very different associations at lower elevation£ Regionally, riparian vegetation represents linear islands that are internally both flortstically and faunistically dynamic rather than mere bridges of homogeneous vegetation in landscape network~ The significance of riparian vegetation as habitat for western birds has been defined primartly at the local level Conservation activities fatmring site dimity are short.sightea[ however, and could have severe consequences for unique elements of riparian avifauna~ Conservation actions must evaluate how local activities alter potential dispersal opportunities for ecological-generalist versus riparian-obligate specie~ Maintaining the character and integrity of riparian avifaunas requires planning from regional and continental perspective~ Perspectivas de escala sobre la diversidad de ayes en ecosistemas riberefios del oeste Resumen: La conservaci6n de ia vegetaci6n riberefm en el oeste de Am&rica del Norte ha enfatizado en parte la provi-si6n de hdbitats para una avifauna localmente diversct La diversidad de sitiog en especial relativos al nt~mero de especies presente~ es generalmente alta en avifaunas rtbereBa~ La dtversidad entre hd.bitats cambtag a lo largo* de una cuenc~ con eusambles ae especies ri~ diflriendo rods de los ensambles de tierras altas en las elevaciones menores y mayore~ Este patr6n puede set atrihuido al realce de los movimientos de las aves dentro de la vegetaci6n ribere~ Los corredores para el movimiento de ave~ a su vez, facilitan la mezcla fauntstica a una escala mas ampit¢ tnfluenciando la diversidad regional dentro de los paisaje.z Los eco-sisterm~ ribere~os son vistos como conectores de forestas a lo largo de paisaJes fragmentado~ En ambtentes del oest¢ sin embargo, estos son forestas altamente ltnearizadas que atraviezan cuencas entre asociaciones de tterras altas de gran elevaci6n y asociaciones muy diferentes en elevaciones menore~ Regionalment~ la vegetaci6n riberegua repmenta islas tineares que son internamente dindmtcas tanto floristtca como fauntsticament~ no siendo meros puentes de ve-getaci6n homogd, nea en redes de paisajex El significado de la vegetact6n ribem~ como hdbitats para aves del...