ABSTRACT. A fundamental assumption of avian survival analysis is that the act of capture, handling, and marking birds does not affect subsequent survival. This assumption is violated when animals experience injury, physiological stress, or disorientation during capture and handling that increases their mortality risk following release. Such capture-related effects must be accounted for during analysis, typically by censoring individuals from the survival history, to avoid biasing the resulting survival estimates. We reviewed studies of radio-marked upland game birds to characterize researcher approaches for addressing short-term effects of capture on survival, and used data from a study of Ruffed Grouse (Bonasa umbellus) to illustrate an empirical approach for evaluating such effects and identifying time thresholds to censor individuals that die shortly following release. A majority of studies (65%) reported using some form of censoring for mortality that occurred within one to three weeks after release, although only 8% of studies reported an empirical approach to identify a threshold for censorship. We found that Ruffed Grouse mortality was greater from one to six days following release when compared with 7 to 30 days. This threshold, and the proportion of birds censored as a result of it, is consistent with a number of previous studies of radio-marked Ruffed Grouse. We also found that short-term mortality of Ruffed Grouse following release was reduced by checking traps twice each day and by adequately concealing traps. We recommend that future studies of radio-marked birds employ empirical methods for detecting postrelease mortality thresholds, which will allow for reduced bias while minimizing unnecessary censorship of birds that die for reasons unrelated to capture.Détection de la mortalité attribuable à la capture chez des oiseaux marqués par radiotélémétrie RÉSUMÉ. L'analyse de la survie des oiseaux repose sur l'hypothèse de base voulant que l'acte de capturer, manipuler et marquer des oiseaux n'affecte pas leur survie subséquente. Cette hypothèse est violée lorsque les animaux subissent des blessures, un stress physiologique ou une désorientation pendant la capture et la manipulation, puisque leur risque de mortalité une fois relâchés augmente du coup. Ces effets imputables à la capture doivent être considérés au moment des analyses, en suivant habituellement l'histoire de survie des individus, afin que les estimations de la survie ne soient pas biaisées. Nous avons passé en revue des études réalisées sur des oiseaux terrestres considérés comme gibier afin de caractériser les approches utilisées par les chercheurs pour tenir compte des effets à court terme de la capture sur la survie. Nous avons également utilisé les données d'une étude sur la Gélinotte huppé (Bonasa umbellus) afin de présenter une approche empirique destinée à évaluer ces effets et à déterminer les seuils temporels où on devrait interrompre le suivi des individus qui meurent rapidement une fois relâchés. La majorité des études (65 %) ra...
Understanding population dynamics is central to population management, particularly for game species that experience human harvest and non‐harvest mortality. Ruffed grouse (Bonasa umbellus) are a widely distributed and common game species in North America that have experienced population declines along their southern range margins, including portions of New England, primarily in response to forest succession and habitat loss. In the state of Maine, ruffed grouse are generally considered abundant, but there is a lack of state‐specific knowledge of ruffed grouse survival and harvest rates to inform harvest management. We estimated seasonal and annual survival rates, harvest rates, and documented cause‐specific mortality of 248 radio‐marked ruffed grouse at 2 study areas in central Maine from 2014 to 2016. We used Program MARK to evaluate sources of spatial, temporal, and individual variation that may affect ruffed grouse survival and harvest. Survival was lowest during October and during winter, and adult ruffed grouse had a higher survival probability than juveniles throughout the year with mean annual survival probabilities of 0.28 ± 0.01 (SE) and 0.13 ± 0.003, respectively. Harvest rates were greater in a state‐owned Wildlife Management Area and were lower within commercially managed private forest that was open to public hunting. Harvest results suggest harvest (H) was greatest at the beginning of the hunting season (Oct; Frye Mountain HOct = 0.14 ± 0.02; Stud Mill HOct = 0.07 ± 0.02), and was lower later in the season (Nov and Dec; Frye Mountain HNov‐Dec = 0.07 ± 0.02; Stud Mill HNov‐Dec = 0.03 ± 0.01). Pooled across all years and study areas, the ruffed grouse harvest rate was 0.16 (95% CI = 0.14–0.18). Our results are comparable to other range‐wide studies and suggest that current hunting regulations for ruffed grouse in Maine are consistent with sustainable population management. © 2018 The Wildlife Society.
Effective wildlife management requires a broad understanding of how forest structure and composition influence habitat use and vital rates during all aspects of species' life‐cycles, however habitat characteristics may have variable importance during different life phases. Even though the ruffed grouse Bonasa umbellus is a popular game bird that has long been a focal species for management, a greater understanding of the links between forest characteristics and components of ruffed grouse reproduction would enhance managers' ability to promote the species. We monitored 45 nests belonging to 37 females during 2015–2017 in central Maine, USA, and evaluated the influence of forest characteristics on nest‐site selection, nest survival and female survival while nesting. Ruffed grouse females selected nest sites with greater horizontal visual obstruction (β = 0.16 ± 0.06 85% CI) than found at other sites that were locally available to them, however this characteristic did not appear to improve nest survival or female survival while nesting. Cumulative nest success was 42.8% and daily nest survival was reduced when coarse woody debris (CWD) was present at nest sites (β = –0.41 ± 0.33 85% CI), but we found no evidence that other habitat characteristics or features of nests themselves were related to nest survival. However, reduced female survival while nesting was associated with presence of CWD (β = –1.27 ± 0.91 85% CI), greater tree basal area (β = –0.96 ± 0.81 85% CI) and greater conifer stem density (β = –0.45 ± 0.28 85% CI) at nest sites; females had a 74.4% chance of survival during the length of time required to successfully nest. Our results demonstrate the importance of forest characteristics on multiple components of species' nesting ecology, and we provided management suggestions to promote attractive ruffed grouse nesting habitat while potentially mitigating sources of nesting failure.
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