The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Recently, researchers in several areas of ecology and evolution have begun to change the way in which they analyze data and make biological inferences. Rather than the traditional null hypothesis testing approach, they have adopted an approach called model selection, in which several competing hypotheses are simultaneously confronted with data. Model selection can be used to identify a single best model, thus lending support to one particular hypothesis, or it can be used to make inferences based on weighted support from a complete set of competing models. Model selection is widely accepted and well developed in certain fields, most notably in molecular systematics and mark-recapture analysis. However, it is now gaining support in several other areas, from molecular evolution to landscape ecology. Here, we outline the steps of model selection and highlight several ways that it is now being implemented. By adopting this approach, researchers in ecology and evolution will find a valuable alternative to traditional null hypothesis testing, especially when more than one hypothesis is plausible.

https://faculty.washington.edu/skalski/classes/QERM597/papers/Johnson%20and%20Omland.pdf

Model selection in ecology and evolution

Resource selection by animals

Logistic regression has become increasingly popular for modeling nest success in terms of nest-specific explanatory variables. However, logistic regression models for nest fate are inappropriate when applied to data from nests found at various ages, for the same reason that the apparent estimator of nest success is biased (i.e. older clutches are more likely to be successful than younger clutches). A generalized linear model is presented and illustrated that gives ornithologists access to a flexible, suitable alternative to logistic regression that is appropriate when exposure periods vary, as they usually do. Unlike the Mayfield method (1961, 1975) and the logistic regression method of Aebischer (1999), the logistic-exposure model requires no assumptions about when nest losses occur. Nest survival models involving continuous and categorical explanatory variables, multiway classifications, and time-specific (e.g. nest age) and random effects are easily implemented with the logistic-exposure model...

https://www.jstor.org/stable/pdfplus/4090416.pdf

A unified approach to analyzing nest success

https://crrc.unh.edu/sites/crrc.unh.edu/files/ei_1485.pdf

From comparative risk assessment to multi-criteria decision analysis and adaptive management: recent developments and applications.

Etude de la reproduction chez cinq especes, Casmerodius albus, Egretta tricolor, E. caerulea, E. Ahula et Endocimus albus dans les Everglades. Le succes de nidation et le nombre de couples sont analyses en relation avec les variations des precipitations et des conditions de la surface de l'eau

Nesting success of five ciconiiform species in relation to water conditions in the Florida Everglades

Many aspects of the influences of forest management activities on bats (Chiroptera) in the Pacific Northwest are poorly known, We compared thinned and unthinned forest stands of the same age and old-growth forest stands to determine potential differences in structure and amount of use by bats. We hypothesized that activity levels of bats would differ in stands differing in structure as a result of management bistory and that activity of bats would be similar in stands of similar structure. We used automated ultrasonic detectors (Anabat II) to record calls of bats in 50-100-year-old thinned and unthinned stands, and in old-growth (200 yr old) stands in the Oregon Coast Range during the summers of 1994 and 1995. Our median index of bat activity was higher in old-growth than in unthinned stands and higher in thinned than in unthinned stands, We were not able to detect a significant difference between the index of median bat activity for old-growth and thinned stands. More than 90% of identifiable passes were identified as calls from Myotis species. The 3 stand types we examined differed in certain structural characteristics such as density and size of trees, and amount of overstory and understory cover. We concluded that the structural changes caused by thinning may benefit bats by creating habitat structure in young stands that bats are able to use more effectively.

Bat activity in thinned, unthinned, and old-growth forests in western Oregon

Two techniques were used to determine the diets of 4 pairs of nesting golden eagles (Aquila chrysaetos) in southwestern Idaho during 1978 and 1979; direct observations of prey deliveries to nests were compared with estimates of food habits derived from analyses of systematic collections of pellet and prey remains. There was no difference (P > 0.05) between the 2 methods in the estimated species composition, either by percent frequency or percent biomass. Comparisons of the daily capture rates derived using the 2 techniques demonstrated that collections of pellet and prey remains consistently underestimated observed prey delivery. Estimates of the time period collections reflected prey deliveries ranged from 1.6 to 5.5 days, but were consistent for each nest. Periodic observations of food delivery at nest sites can be used to correct for prey biomass unaccounted for in the collections; this procedure would enable researchers to use collections of pellet and prey remains to estimate prey biomass delivered to nests. J. WILDL. MANAGE. 47(2):360-368 Early work on the diets of birds of prey was based largely on analyses of stomach contents (Fisher 1893, McAtee 1935, Arnold 1954). More recently, investigators have concentrated research efforts on assessing the food habits of free-living raptors. The vast majority of these studies depended on interpretation of pellet and prey remains collected at nests (Craighead and Craighead 1956, Smith and Murphy 1973) and reported species composition qualitatively as percent frequency or biomass. Unfortunately, these studies were unable to estimate the daily and total biomass of prey captured and delivered to nests. Recently some investigators have used direct observations from blinds to assess the biomass of prey delivered to nests (Snyder and Wiley 1976, Newton 1978). Although direct observation is the most reliable method to assess the frequency and biomass of prey delivered to nests, it is too time-consuming to be a viable technique for most population studies. Most research on the food habits of golden eagles has depended on analyses of pellet and prey remains found on nests (Carnie 1954, Lockie 1964, Arnell 1971, Mollhagen et al. 1972, Lockhart 1976, Olendorff 1976). A few studies have derived quantitative estimates of the food requirements of golden eagles by using captive (Fevold and Craighead 1958) and wild (Brown and Watson 1964, McGahan 1967) birds. However, no study has tested the relationship between species composition estimates (percent frequency and biomass) derived from collections of pellet and prey remains and those based on observed prey deliveries. Furthermore, no previous studies have tested the feasibility of using periodic direct observation in concert with pellet and prey remains collections to generate prey biomass estimates. This paper evaluates these 2 methods and discusses ways in which collections of pellet and prey remains may be used to estimate the biomass of prey brought to the nest. This study is part of the Snake River Birds of Prey Research Project and was funded largely by the Bureau of Land Management. Partial funding also was I Contribution 3655 of the Journal Series, Florida Agricultural Experiment Station, Gainesville, FL 32611. 360 J. Wildl. Manage. 47(2):1983 GOLDEN EAGLE FOOD HABITS * Collopy 361 provided by the National Wildlife Federation, Sigma Xi, and the University of Michigan. Many individuals assisted throughout this study; in particular, I thank D. McCullough, R. Storer, G. Fowler, J. Diana, and R. Drobney. M. Kochert, D. Blasdell, T. Edwards, K. Steenhof, G. Smith, and A. Bammann also assisted throughout the study. I especially thank L. Farley for care in analyzing the collections of pellet and prey remains. S. Beissinger, M. Kochert, R. Labisky, W. Marion, T. O'Meara, and K. Steenhof reviewed the manuscript. STUDY AREA AND METHODS The study area was along the Snake River Canyon and surrounding upland desert plateau south of Boise, Idaho, in Owyhee and Elmore counties. This 195,063-ha area, known as the Snake River Birds of Prey Area (BPA), was administered by the Bureau of Land Management. The BPA lies within the Great Basin semidesert scrub biome described by Whittaker (1975); the major vegetation communities in the area have been previously described (U.S. Dep. Inter. 1979). Four pairs of golden eagles were observed throughout the nesting season at 4 sites in both 1978 and 1979. Photographs showing unique plumage characteristics of the breeding adults in 1978 and in 1979 revealed that the same pairs nested at the same sites in both years. Thus, betweenyear comparisons of results at each study site were possible. Because each breeding pair successfully fledged young in 1978, and subsequently nested in the same nest in 1979, I assumed that investigator interference was minimal. Systematic observations of eagles were made during the brood-rearing period from blinds placed 15-40 m away. Dawnto-dark observations were not possible because the entry to each blind was in full view of the nest; it was believed that activity near the blinds during early morning and late evening would frighten the adults from the nest, unnecessarily exposing the young to chilling temperatures. Consequently, I entered each blind at approximately midday and observed the nest until dark. I then slept in the blind and continued observations the next morning from first light until approximately noon. At the end of an observation period at 1 nest, I immediately moved to the next study site and continued observations using the same procedure. This sampling strategy was used to monitor each of the 4 study nests once every 6th day. All prey items delivered to the nest during each observation period were identified to species, assigned to a size class, and if possible, classified by sex. The proportion of the carcass delivered, time of day, and sex of the eagle delivering the prey were also recorded. Black-tailed jack rabbits (Lepus californicus) were known to be the most common prey item found in nests of this eagle population (U.S. Dep. Inter. 1979). To obtain greater resolution in the estimate of lagomorph biomass delivered to the nest, 6 adult jack rabbits were dismembered and the mean percentage of total body weight contained in 5 portions of the carcass was determined: entire (100%), headless (90.5 ? 1.2%), back 3/4 (83.5 + 1.4%; head and forelegs missing), back ?1/ (53.5 ? 1.1%; head, forelegs, and part of rib cage missing), and hindquarters (38.3 ? 1.0%; pelvis and hindlegs only). The actual biomass of black-tailed jack rabbit and Nuttall's cottontail (Sylvilagus nuttallii) carcasses delivered to nests was estimated using the portion of the body present and its fraction of the mean weight of the entire animal. The actual biomass of other prey delivered was estimated using the proportion of the total J. Wildl. Manage. 47(2):1983 362 GOLDEN EAGLE FOOD HABITS * Collopy carcass present as the proportion of total prey biomass delivered. I assumed that at least a portion of all prey captured by adult eagles during the brood-rearing phase was delivered to the nest. This assumption may have slightly underestimated the total number of prey captured, but did not significantly affect the species composition of the diet at the nest site. Both the biomass of an entire prey item and the actual amount delivered to the nest were estimated. For clarity these will be referred to as the biomass of prey "captured" and "delivered." After each observation period, I entered the nest and verified the identification of all prey items previously delivered. All inedible prey remains and reguritated pellets found at the nest were collected (only the head, feet, and tail of fresh prey remains were collected) and later identified. The number of prey items in the pellets was determined by the maximum number of body parts present (e.g., femurs, feet, mandibles). The species and size class of each prey item were identified by comparison with study skins, skeletons, and hair specimens. The number of prey items counted in the pellets was compared with the number counted from fresh remains and those counted in the previous collection. Whenever a prey item in the pellet appeared to duplicate a previously counted item (e.g., in fresh remains or previous collection), it was not considered an additional individual. The total biomass represented by each species identified in the collections of prey remains was calculated using published weight data. Mammal weights were obtained from Hall (1946), Burt and Grossenheider (1964), Schreiber (1973), Armitage et al. (1976), and U.S. Dep. Inter. (1979). Bird weights were taken from Esten (1931), Galbreath and Moreland (1953), Nelson and Martin (1953), Craighead and Craighead (1956), Anderson (1969), Vermeer (1970), Fimreite (1971), Balph (1973), Marti (1973), and U.S. Dep. Inter. (1979). Weights of reptiles were obtained from U.S. Dep. Inter. (1979). All statistical comparisons of percent frequency and biomass of prey delivered to nests were made using 6 major prey categories: Lepus californicus, Sylvilagus nuttallii, Marmota flaviventris, small rodents (Heteromyidae, Cricetidae, and all other Sciuridae), large nonpasserines (Phasianidae and Corvidae), and miscellaneous birds and reptiles. All data were analyzed using an Amdahl 470/V7 computer and the University of Michigan Terminal System (MTS). Statistical analyses were conducted using the Michigan Interactive Data Analysis System (MIDAS). Statistical procedures used to analyze the data included both paired and 2-sample t tests (Remington and Schork 1970). To meet the assumptions of the statistical models, percentage data were arcsine transformed prior to analysis whenever they were outside the interval between 30 and 70%.

A Comparison of Direct Observations and Collections of Prey Remains in Determining the Diet of Golden Eagles

Le comportement fratricide chez les Accipitridae apparait lie a des differences relatives de taille au sein de la fratrie, differences elles-memes liees au temps ecoule entre les eclosions, aux differences de poids a l'eclosion, peut-etre au sexe

Obligate and Facultative Brood Reduction in Eagles: An Examination of Factors That Influence Fratricide

The wildlife profession has a long-established tradition of examining and debating the quality and direction of wildlife research (Scheffer 1976, Romesburg 1981, Bailey 1982, McCabe 1985, Capen 1989, Nudds and Morrison 1991, Lancia et al 1993) This introspection is good, for it encourages the profession to improve and mature In this essay, we provide what we hope will be a significant milepost in that process by advocating a general philosophy and protocol for wildlife research and management Rather than articulating a list of specific research priorities and reiterating the need for additional research money, we encourage an encompassing, fundamental shift that will promote more efficient use of current research and management dollars Over the last several years, various groups and many individuals interested in the management of natural resources have recognized a need for reform in natural resources-related research These include the Ecological Society of America's Committee for a Research Agenda for the 1990's (Lubchenco et al 1991), the National Research Council's Committee on Forestry Research (Comm For Res 1990), the Society of American Forester's Task Force on Sustaining Long-term Forest Health and Productivity (Soc Am For 1993) and many others (Brussard 1991; Brussard and Ehrlich 1992; Levin 1992a,b; Levin 1993) There appears to be a general consensus that change is due Furthermore, intensifying political debates about management of natural resources (eg, timber harvests and ancient forests, sustainable development, and the preservation-conservation of biodiversity) call for integrated research and management to address uncertainty in wildlife and ecosystem management and thereby ameliorate controversy in the future (Clark 1992, Ludwig et al 1993, Ludwig 1994) Research and management can no longer afford to be "two solitudes"; distinctions between basic and applied research have blurred (Nudds 1979, Moffatt 1994) The central issue is the application of sound scientific principles to solve problems

/pdf/arm-for-the-future-adaptive-resource-management-in-the-tnkl8g8cb7.pdf

Michael W. Collopy

Papers

Nesting success of five ciconiiform species in relation to water conditions in the Florida Everglades

Bat activity in thinned, unthinned, and old-growth forests in western Oregon

A Comparison of Direct Observations and Collections of Prey Remains in Determining the Diet of Golden Eagles

Obligate and Facultative Brood Reduction in Eagles: An Examination of Factors That Influence Fratricide

ARM! For the Future: Adaptive Resource Management in the Wildlife Profession