Geology topics

Joel A. Schmutz

Publications and source records attributed to Joel A. Schmutz.

116 records · Page 7Linked to original sources

USGS1995

Survival estimation and the effects of dependency among animals

Survival models assume that fates of individuals are independent, yet the robustness of this assumption has been poorly quantified. We examine how empirically derived estimates of the variance of survival rates are affected by dependency in survival probability among individuals. We used Monte Carlo simulations to generate known amounts of dependency among pairs of individuals and analyzed these data with Kaplan-Meier and Cormack-Jolly-Seber models. Dependency significantly increased these empirical variances as compared to theoretically derived estimates of variance from the same populations. Using resighting data from 168 pairs of black brant, we used a resampling procedure and program RELEASE to estimate empirical and mean theoretical variances. We estimated that the relationship between paired individuals caused the empirical variance of the survival rate to be 155% larger than the empirical variance for unpaired individuals. Monte Carlo simulations and use of this resampling strategy can provide investigators with information on how robust their data are to this common assumption of independent survival probabilities.

Journal of Applied Statistics↗

USGS1994

Emperor goose (Chen canagica)

Early naturalists exploring western Alaska were intrigued to find a stocky, blue-gray species of coastal goose unique to that area and nearby Russia. As E. W. Nelson (1887) wrote, "Among the various species of birds more or less peculiar to Alaska this goose is perhaps the most noteworthy." The Emperor Goose nests in the extensive coastal salt marsh habitats of arctic and sub-arctic Alaska and Russia and winters primarily on coastal beaches along ice-free areas of the Aleutian Islands and the Alaska Peninsula. Locally known as the "Beach Goose" from its habit of roosting and feeding near the waters' edge, the diet of this species consists largely of clams, mussels, and algae when wintering and staging in marine and estuarine habitats. When nesting in terrestrial habitats, it eats mostly roots, bulbs, and shoots of vegetation. Although the breeding biology and habitat requirements of this goose have been examined in detail, mostly on the Yukon-Kuskokwim Delta (Y-K Delta) of Alaska, there have been no intensive studies of its wintering or staging biology. Recent studies of migration have confirmed pathways and timing between the Y-K Delta and staging areas on the Alaska Peninsula and wintering areas largely on the Aleutian Islands (Hupp et al. 2007). Observations of substantial molt migrations to the Chukotka Peninsula in eastern Russia (Hupp et al. 2007) suggest a possible change in distribution, or at least a clarification, and raise the possibility of harvest mortality on both continents. Alaska's Emperor Goose population declined precipitously from 139,000 in 1964 to 42,000 in 1986, although its numbers have recovered slightly since then (Fischer et al. 2008). The factors responsible for this quick decline and slow recovery remain poorly known. Hunting, especially subsistence hunting by Native Americans, is probably a factor (Hupp et al. 2008b); coastal oil pollution could also be reducing the survival of overwintering individuals (Byrd et al. 1995); and interspecific competition among brood rearing geese may limit recovery through recruitment (Schmutz and Laing 2002, Lake et al. 2008).

Birds of North America↗

USGS1994

Seasonal and annual survival of emperor geese

Population levels of emperor geese ( Chen canagica ) in Alaska in 1993 were about half that estimated in the 1960s. Survival information is necessary for managers to decide how to best enhance recovery of this species to former levels. We calculated seasonal and annual estimates of emperor goose survival from resightings of neck-collared birds. Geese were neck collared in 1988-90 on their breeding grounds in the Yukon-Kuskokwim Delta, Alaska, and resighted each spring and fall, 1988-92, at staging areas on the Alaska Peninsula. Adult monthly survival rates during overwinter periods (1 Oct-30 Apr) were not different (P = 0.281) among years ( Ŝ' = 0.940, SE = 0.009), whereas monthly rates of oversummer (1 May-30 Sep) survival showed annual variation (P = 0.048). However, we constrained oversummer survival to a single estimate of 0.980 (0.010). Monthly survival estimates for juveniles during their first overwinter period did not vary among years (P = 0.999) and was 0.710 (0.018). Subsequent monthly survival for juveniles was 0.943 (0.010), similar to that for adults. We developed an adjustment procedure to account for philopatric behavior of geese and this enabled us to use data for postbanding (1 Aug-30 Sep) periods. Survival estimates were low compared with those for other goose species, particularly for juveniles. We addressed collar loss and heterogeneity in resighting probabilities and felt their contribution to potential model bias was insignificant. Annual survival among adults (Ŝ' = 0.631, SE = 0.023) was not different (P = 0.709) from that observed during 1982-85 (Petersen 1992). The similarity in survival rates in these studies suggests that harvest regimes did not differ between the 2 periods. This suggests that continued subsistence harvest has contributed to persistent low population levels in emperor geese.

Alaska↗

USGS1993

Survival and pre-fledging body mass in juvenile emperor geese

A positive relationship exists between fledgling body mass and juvenile survival for some altricial (Krementz et al. 1989, Magrath 1991, Linden et al. 1992) and precocial (Owen and Black 1989, Longcore et al. 1991, Francis et al. 1992) species. Because the energetic demands of migration are high, physiologic condition may be a proximate determinate of juvenile survival in geese. Owen and Black (1989) found that pre-fledging body mass of Barnacle Geese ( Branta leucopsis ) was positively related to juvenile survival to winter. First-year survival in Lesser Snow Geese ( Chen caerulescens caerulescens ) was also affected by pre-fledging body mass (Francis et al. 1992). It is not clear, however, when such mass-related mortality occurs. Both species migrate >3,000 km to wintering areas, but make use of fall staging areas while en route (Owen 1980, Francis and Cooke 1992). Survival fo geese between fledging and staging areas has not been addressed. Measurement of survival during this interval could provide insight to the timing of juvenile mortality in arctic geese.

Alaska↗

USGS1990

Error in telemetry studies: Effects of animal movement on triangulation

We used Monte Carlo simulations to investigate the effects of animal movement on error of estimated animal locations derived from radio-telemetry triangulation of sequentially obtained bearings. Simulated movements of 0-534 m resulted in up to 10-fold increases in average location error but <10% decreases in location precision when observer-to-animal distances were <1,000 m. Location error and precision were minimally affected by censorship of poor locations with Chi-square goodness-of-fit tests. Location error caused by animal movement can only be eliminated by taking simultaneous bearings.

Journal of Wildlife Management↗

USGS1990

Brood habitat use of Rio Grande wild turkeys

Habitat use of 14 Rio Grande wild turkey ( Meleagris gallopavo ) broods was studied in riparian habitats in northeast Colorado in 1986-87. Of 191 locations, 78% were within the riparian zone, 11 % in agricultural uplands, and 11 % on the edge between these habitats. Use of habitats was dependent on time of day. Within the riparian zone, older broods used grazed areas more often than young broods. Microhabitat use was examined at 35 brood and 29 random locations within the riparian zone. Plots used by young broods had higher frequencies of grasses than random plots.

Colorado↗

USGS1989

Reproductive performance of Rio Grande wild turkeys

Frequency, magnitude, and timing of reproduction in Rio Grande Wild Turkey ( Meleagris gallopavo intermedia ) hens were studied in northeastern Colorado in 1986 and 1987. All adults (n = 12) and 95% (n = 20) of yearlings were known to attempt nesting. Adults initiated first nest attempts earlier than yearlings in 1987 but not 1986. Adults and yearlings did not differ in clutch size or nesting success. There was an inverse relationship between clutch size and initiation date of first nests by adults. Clutch and egg size, however, were not related. Among yearlings, body mass at capture in February was positively correlated with subsequent nest-initiation date. Environmental and social stimuli, but not winter severity, are hypothesized proximate conditions regulating reproduction in this Wild Turkey population.

The Condor↗

USGS1989

Nest habitat use of Rio Grande wild turkeys

Nest habitat use of Rio Grande Wild Turkeys ( Meleagris gallopavo intermedia ) was studied along the South Platte River in northeast Colorado in 1986-87. Thirty-three of 35 nests were in riparian habitats. Nests were either in western snowberry ( Symphoricarpos occidentalis ) (67%) or mixed forbs and grasses (33%). Early season nests were more likely to be in snowberry than late season nests. Nest sites were characterized by greater overstory canopy cover, more shrubs, fewer grasses, and greater understory cover and height than surrounding areas. These areas had more shrubs, fewer large trees, and greater understory cover and height than riparian habitats throughout the study area. Phenology of understory vegetation and the effect of such vegetation on nest predation may influence temporal patterns of nest habitat use.

The Wilson Bulletin↗