Suchergebnisse

Context
Diet selection is studied in herbivores using three predominant methods: (1) microhistological surveys (identification of plants cell walls remaining in gut contents or faecal excretions); (2) direct bite counts (of tame animals); and (3) indirect bite counts (identifying herbivory on damaged plant tissues). Microhistological surveys and direct bite counts are accurate and provide the potential advantage of linking diet selection to particular individuals. Also, they allow diet selection to be measured in systems with sympatric herbivores more easily than indirect bite counts. However, they require expertise in cell wall structure identification or access to tame animals, and generally require greater expense than indirect bite counts. Conversely, indirect bite counts have the advantages of relatively low cost and time commitment for gathering data and do not require animal observation, but may not be accurate.

Aims
We tested for similarity between diet-selection estimates calculated by indirect bite counts and microhistological surveys.

Methods
We performed concurrent indirect bite count and faecal microhistological surveys on white-tailed deer (Odocoileus virginianus) at Fort Bragg Military Installation, NC.

Key results
The indirect bite count survey assignment of selection was 48% similar to assignments derived from the microhistological survey, based on Jaccard's similarity index. Out of 23 plant species determined to be selected by indirect bite counts, 15 of those species were selected according to microhistological surveys. According to the microhistological survey, eight of the selected plants made up 51% of the overall diet, and seven of those eight were selected according to the indirect bite counts.

Conclusions
Our data indicate that indirect bite counts may provide a relatively accurate index of the deer-selected plants most important in the white-tailed deer diet, but may be less appropriate to determine selection of plants that infrequently occur in their diet, plants that are typically consumed in entirety, or plants where herbivory damage is poorly identified.

Implications
Indirect bite counts are a relatively inexpensive and time-efficient tool that may be useful to determine plant species most important to white-tailed deer within a forested landscape, particularly if additional research can improve on associated inaccuracies.

Context Over the past two decades, an increase in the number of resident (non-migratory) Canada geese (Branta canadensis) in the United States has heightened the awareness of human–goose interactions. Aims Accordingly, baseline demographic estimates for goose populations are needed to help better understand the ecology of Canada geese in suburban areas. Methods As a basis for monitoring efforts, we estimated densities of adult resident Canada geese in a suburban environment by using a novel spatial mark–resight method. We resighted 763 neck- and leg-banded resident Canada geese two to three times per week in and around Greensboro, North Carolina, over an 18-month period (June 2008 – December 2009). We estimated the density, detection probabilities, proportion of male geese in the population, and the movements and home-range radii of the geese by season ((post-molt I 2008 (16 July – 31 October), post-molt II 2008/2009 (1 November – 31 January), breeding and nesting 2009 (1 February – 31 May), and post-molt I 2009). Additionally, we used estimates of the number of marked individuals to quantify apparent monthly survival. Key results Goose densities varied by season, ranging from 11.10 individuals per km2 (s.e. = 0.23) in breeding/nesting to 16.02 individuals per km2 (s.e. = 0.34) in post-molt II. The 95% bivariate normal home-range radii ranged from 2.60 to 3.86 km for males and from 1.90 to 3.15 km for females and female home ranges were smaller than those of male geese during the breeding/nesting and post-molt II seasons. Apparent monthly survival across the study was high, ranging from 0.972 (s.e. = 0.005) to 0.995 (s.e. = 0.002). Conclusions By using spatial mark–resight models, we determined that Canada goose density estimates varied seasonally. Nevertheless, the seasonal changes in density are reflective of the seasonal changes in behaviour and physiological requirements of geese. Implications Although defining the state–space of spatial mark–resight models requires careful consideration, the technique represents a promising new tool to estimate and monitor the density of free-ranging wildlife. Spatial mark–resight methods provide managers with statistically robust population estimates and allow insight into animal space use without the need to employ more costly methods (e.g. telemetry). Also, when repeated across seasons or other biologically important time periods, spatial mark–resight modelling techniques allow for inference about apparent survival.