Robert E. Kenward

Compositional Analysis of Habitat Use From Animal Radio‐Tracking Data

Analysis of habitat use based on radio-tagged animals presents difficulties inadequately addressed by current methods. Areas of concern are sampling level, data pooling across individuals, non-independence of habitat proportions, differential habitat use by groups of animals, and arbitrary definition of habitat availability. We advocate proportional habitat use by individual animals as a basis for analysis. Hypothesis testing of such nonstandard multivariate data is done by compositional analysis, which encom- passes all MANOVA/MANCOVA-type linear models. The applications to habitat use range from testing for age class effects or seasonal differences, to examining relationships with food abundance or home range size. We take as an example the comparison of habitat use and availability. The concepts are explained and demonstrated on two data sets, illustrating different methods of treating missing values. We compare utilized with available habitats in two stages, examining home range selection within the overall study area first, then habitat use within the home range. At each stage, assuming that use differs from random, habitats can be ranked according to relative use, and significant between-rank differences located. Compositional analysis is also suited to the analysis of time budgets or diets.

Goshawk Hunting Behaviour, and Range Size as a Function of Food and Habitat Availability

(1) Four released goshawks were radio-tracked for up to 29 days at a time in Oxfordshire. Their hunting flights were mostly at 3-4 min intervals, for an average of 200 m in open country. They remained in woodland for 50% of the time although only 12% of their ranges was wooded. This preference resulted not from hawks flying less frequently in woodland, but because they flew half the distance between perches and doubled back twice as often in woodland as in open country. (2) Most attacks were initiated from perches, and only 3% were at prey already in flight. Six percent of observed attacks were successful, but hawks were most successful when hunting out of sight. They killed, on average, once in every 262 minutes of hunting. Seventy percent of prey was taken in or from woodland, a higher proportion than expected from the time spent there. (3) There were no sex or age differences in the preference for woodland of twenty-two wild goshawks radio-tracked in Sweden. Woodland within 200 m of open country was the most preferred habitat, and the majority of kills were made there. Range size was related to the proportion of a range that was woodland edge, and to prey availability. It is suggested that hawks covered the amount of woodland edge which gave adequate kills at the prevailing prey density, range size then being the area which happened to include that amount of woodland edge.

DENSITY AND LINKAGE ESTIMATORS OF HOME RANGE: NEAREST-NEIGHBOR CLUSTERING DEFINES MULTINUCLEAR CORES

Methods used to estimate home ranges from point locations are based either on densities of locations or on link distances between locations. The density-based methods estimate ellipses and contours. The other class minimizes sums of link distances, along edges of polygons or to range centers or between locations. We propose a new linkage method, using nearest-neighbor distances first to exclude outlying locations and then to define a multinuclear outlier-exclusive range core (OEC) by cluster analysis. The assumption behind exclusion of outliers, that movements inside and outside range cores involve different activities, was supported by data from radio-tagged Common Buzzards (Buteo buteo). We compared the new method with other techniques by using location data from each of 28 goshawks, 114 buzzards, 138 gray squirrels, and 14 red squirrels. Range structure statistics from OECs showed marked differences between species in numbers and extent of core nuclei. Range analysis displays illustrated relationships of range area with age categories, food supply, population density, and body mass within species. The OECs gave highly significant results in three of five within-species tests, perhaps because animal movements in these cases were affected by coarse-grained habitat boundaries. When movements were likely to have been influenced by diffuse social interactions and foraging for scattered prey, the most significant results were from density-based estimators, especially kernel contours that had been optimized by least-squares cross validation. We recommend use of both density and linkage estimators of home range until a basis for a priori choices has been established.

Identifying governance strategies that effectively support ecosystem services, resource sustainability, and biodiversity

Conservation scientists, national governments, and international conservation groups seek to devise, and implement, governance strategies that mitigate human impact on the environment. However, few studies to date have systematically investigated the performance of different systems of governance in achieving successful conservation outcomes. Here, we use a newly-developed analytic framework to conduct analyses of a suite of case studies, linking different governance strategies to standardized scores for delivering ecosystem services, achieving sustainable use of natural resources, and conserving biodiversity, at both local and international levels. Our results: (i) confirm the benefits of adaptive management; and (ii) reveal strong associations for the role of leadership. Our work provides a critical step toward implementing empirically justified governance strategies that are capable of improving the management of human-altered environments, with benefits for both biodiversity and people.

Survival and breeding success of reared and wild ring-necked pheasants in Sweden

Little research compares the reproductive performance of game birds reared and released in different ways. Consequently, we studied survival and breeding success of 307 female ring-necked pheasants (Phasianus colchicus) by radio-tracking in Oster-Malma (O-M) and Gotland, Sweden, during 1983-86. All pheasants at O-M were released during spring after they had been reared (fostered) by domestic chickens (n=46) or under lamps (n=78; machine-reared). On Gotland, 114 machine-reared pheasants were released for comparison with 69 radio-tagged wild pheasants. When released in late May, survival was similar (P>0.2) for fostered females (43±8%; x±SE) and machine-reared females (44±9%). However, fostered pheasants had higher clutch survival (P=0.034) and higher brood survival (P=0.023) than machine-reared pheasants

SURVIVAL OF RING-NECKED PHEASANTS WITH BACKPACKS, NECKLACES, AND LEG BANDS

We recorded recovery rates for 300 adult female ring-necked pheasants (Phasianus colchicus) and 150 juveniles (82 M, 68 F) marked with 2 different dummy radio tags or leg bands. Birds with backpack tags in all age and sex categories disappeared more quickly and were recovered by shooting or trapping less often than birds with necklace tags or with leg bands (P < 0.05 for juv and ad F). Survival was not affected by weight of necklaces (15 or 25 g) or by the color of the backpacks (white or brown). Necklace radio tags, at 2-3% of body weight, are more suitable than backpacks for studies of pheasant survival.

SETTING HARNESS SIZES AND OTHER MARKING TECHNIQUES FOR A FALCON WITH STRONG SEXUAL DIMORPHISM

Abstract Backpack radio-tags can be used to monitor survival of raptors for several years after fledging, but may reduce survival if a poor fit results from subjective judgments. We present an attachment method that can use bird measurements to predict harness sizes. Relationships between body mass of Saker Falcons and harness size predicted the size for smaller falcon species. Harnesses were fitted when birds had reached full size in the nest, which required age estimation at a previous visit to predict a fledging date. Equations based on wing length provided objective aging of nestlings. A pump-pressured water gun aided capture of young falcons and toggle-loops restrained the feet during marking. Saker Falcons with radio-tags and others marked only with leg bands and implanted transponders had the same recapture rate (7%) in autumn, indicating similar survival. This retrap rate should be adequate to estimate harvest rates and population sizes for Saker Falcons.

Home range estimation within complex restricted environments: importance of method selection in detecting seasonal change

Estimating the home ranges of animals from telemetry data can provide vital information on their spatial behaviour, which can be applied by managers to a wide range of situations including reserve design, habitat management and interactions between native and non-native species. Methods used to estimate home ranges of animals in spatially restricted environments (e.g. rivers) are liable to overestimate areas and underestimate travel distances by including unusable habitat (e.g. river bank). Currently, few studies that collect telemetry data from species in restricted environments maximise the information that can be gathered by using the most appropriate home-range estimation techniques. Simulated location datasets as well as radio-fix data from 23 northern pike (Esox lucius) were used to examine the efficiency of home-range and travel estimators, with and without correction for unusable habitat, for detecting seasonal changes in movements. Cluster analysis most clearly demonstrated changes in range area between seasons for empirical data, also showing changes in patchiness, and was least affected by unusable-environment error. Kernel analysis showed seasonal variation in range area more clearly than peripheral polygons or ellipses. Range span, a linear estimator of home range, had no significant seasonal variation. Results from all range area estimators were smallest in autumn, when cores were least fragmented and interlocation movements smallest. Cluster analysis showed that core ranges were largest and most fragmented in summer, when interlocation distances were most variable, whereas excursion-sensitive methods (e.g. kernels) recorded the largest outlines in spring, when interlocation distances were largest. Our results provide a rationale for a priori selection of home-range estimators in restricted environments. Contours containing 95% of the location density defined by kernel analyses better reflected excursive activity than ellipses or peripheral polygons, whereas cluster analyses better defined range cores in usable habitat and indicate range fragmentation.

Techniques for evaluating the spatial behaviour of river fish

Radio-tagging is widely used for studies of movements, resource use and demography of land vertebrates, with potential to combine such data for predictive modelling of populations from individuals. Such modelling requires standard measures of individual space use, for combination with data on resources, survival, dispersal and breeding. This paper describes how protocols for efficient collection of space-use data can be developed during a pilot study, and reviews the ways in which such data can be used for space-use indices that help answer biological questions, with examples from a study of riverine pike (Esox lucius). Analyses of diurnal activity and spatio-temporal correlation were used to assess when to record locations, and analyses of home range increments were used to define the number of location records necessary to assess seasonal ranges. We stress the importance of developing protocols that use minimal numbers of locations from each individual, so that analyses can be based on samples of many individuals. The efficacy of link-distance (e.g. cluster analysis) and location density (e.g. contouring) techniques for spatial analysis for river fish were compared, and the utility of clipping off areas to river banks was assessed. In addition, a new automated analysis was used to estimate distances along river mid-lines. These techniques made it possible to quantify interactions between individuals and their habitat: including a significant increase in core range size during floods, significant preference for deep pools, and a lack of exclusive territories.

Is early dispersal enterprise or exile? Evidence from radio-tagged buzzards

In order to test whether Common Buzzards Buteo buteo that dispersed early were entrepreneurs or exiles, we determined standardised autumn ranges by radio-tracking 67 juveniles during 1990-94. Of these, 11 had dispersed more than 2 km from their natal nest, and had therefore left the natal territory. Buzzards that dispersed early had more fragmented ranges than those that delayed dispersal until the following spring; otherwise no range characteristic differed between the two groups. When only the dispersers were considered, increase in distance from the natal nest was associated with a decrease in range size (r = 0.74) and an increase in the proportion of arable land within the range (r = 0.77). Further investigation revealed that range size was affected by distance from the nest but not by arable habitat. The smaller range size of distant dispersers, combined with evidence of increased productivity among them, suggests that they were more likely to have been entrepreneurs than exiles.