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Comment on “Are survival rates for northern spotted owls biased?”

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Loehle et al. recently estimated survival rates from radio-telemetered northern spotted owls (Strix occidentalis caurina (Merriam, 1898)) and suggested that survival rates estimated for this species from capture–recapture studies were negatively biased, which subsequently resulted in the negatively biased estimates of rates of population change () reported by Anthony et al. (Wildl. Monogr. No. 163, pp. 1–47 (2006)). We argue that their survival estimates were inappropriate for comparison with capture–recapture estimates because (i) the manner in which they censored radio-telemetered individuals had the potential to positively bias their survival estimates, (ii) their estimates of survival were not valid for evaluating bias, and (iii) the size and distribution of their radiotelemetry study areas were sufficiently different from capture–recapture study areas to preclude comparisons. In addition, their inferences of negative bias in rates of population change estimated by Anthony et al. were incorrect and reflected a misunderstanding about those estimators.

Loehle et al. ont récemment estimé par radiotélémétrie les taux de survie de la chouette tachetée du Nord (Strix occidentalis caurina (Merriam, 1898)) et ils laissent entendre que les taux de survie estimés chez les chouettes tachetées dans les études de capture–recapture sont faussés négativement, ce qui a entraîné des erreurs négatives dans les estimations des taux de changement démographique () signalés chez les populations de chouettes tachetées par Anthony et al. (Wildl. Monogr. No. 163, pp. 1–47 (2006)). Nous soutenons que leurs estimations de survie ne peuvent être comparées adéquatement à des estimations provenant de captures–recaptures parce que (i) la façon dont ils ont mené leur inventaire par radio-télémétrie peut potentiellement introduire une erreur positive dans leurs estimations de survie, (ii) leurs estimations de survie ne peuvent validement servir à déterminer l’erreur et (iii) la taille et la répartition des sites qu’ils ont étudiés par radio-télémétrie sont suffisamment différentes de celles des sites étudiés par capture–recapture pour empêcher les comparaisons. De plus, leur déduction d’une erreur négative dans les taux de changement démographique estimés par Anthony et al. est erronée et reflète une mauvaise interprétation des estimateurs.

Document Type: Discussion

Publication date: September 1, 2006

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