Demography of Mexican spotted owls in the Sacramento Mountains, New Mexico

Abstract

Information on population dynamics is key to gauging the status of threatened or endangered species. We monitored demography of a population of threatened Mexican spotted owls (Strix occidentalis lucida) in the Sacramento Mountains, New Mexico from 2003 to 2011. We estimated reproductive output for territorial pairs of owls; used mark‐recapture methodology and Pradel's reparameterized Jolly‐Seber models to estimate annual apparent survival rates, recapture rates, recruitment rates, and annual rate of population change (λRJS) for 2005–2009; and used estimates of λRJS to assess short‐term population viability. Reproductive output was highly variable for 2004–2011, whereas annual apparent survival and recapture rates were less variable among years. Annual rates of population change exceeded 1.0 for both sexes from 2005 to 2009, and empirical observations of numbers of territorial owls supported the model‐based trend estimate. Abundance of territorial owls was strongly related to reproduction within the study area, suggesting that population change was driven largely by internal processes. Population viability analyses suggested that population growth was likely to continue in the short term if current conditions persist. The positive growth rates observed in our study populations are encouraging, and may indicate that current recommendations for recovering this owl are succeeding. However, our estimates of λRJS covered a very short time period, given both the potential lifespan of Mexican spotted owls and the extent of temporal variability in weather typical of the southwestern United States. Longer studies of owl demography than we present will be required to understand long‐term population trends, and such studies should extend across the range of the subspecies. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

A review of survival estimates for raptors and owls

“…, Ganey et al . ). In populations of long‐lived eagles, in which competition for places in the breeding population is often high, mortality rates among late‐aged subadults may also be high (e.g.…”

“…Most attention has been directed to species that suffered severe population declines or were considered threatened or endangered for other reasons (e.g. Newton 1986, Ratcliffe 1993, Anthony et al 2006, Forsman et al 2011, Ganey et al 2014.…”

“…Among these studies, some reported sex-, age-, region-or time-specific variation in survival , Martin et al 2006, Karell et al 2009, Forsman et al 2011, Ganey et al 2014, while others simply provided estimates of overall, or prebreeder and breeder survival (Table S1). As a consequence of the difficulties of recapturing, re-sighting or tracking birds until they become breeding adults, and the limited use of the relatively new statistical models developed to deal with such difficulties, estimates of juvenile and prebreeding survival were fewer, more variable and probably less reliable than estimates of adult survival, especially for species with delayed maturity (see below).…”

“…It would be expected that young birds, because of their inexperience and low social status, would survive less well than older individuals. Most studies reporting age-specific estimates indicated that annual survival rates of juveniles or subadults were substantially lower than those of adults of the same species (for exceptions see Bowman et al 1995 , Sergio et al 2011, Tenan et al 2012, Ganey et al 2014. In populations of long-lived eagles, in which competition for places in the breeding population is often high, mortality rates among lateaged subadults may also be high (e.g.…”

The interacting effects of food, spring temperature, and global climate cycles on population dynamics of a migratory songbird

“…The Pradel model accounts for imperfect detection probability (P) in the encounter history, reducing potential bias in the estimates of φ, f, and k (Lebreton et al, 1992), and has been applied to demographic analyses of a number of species [e.g. owls (Franklin et al, 2004;Ganey et al, 2014), neotropical parrots (Sandercock & Beissinger, 2002), bears (Boulanger et al, 2002), and migrating songbirds (Schaub et al, 2001)].…”