Effects of fat reserves on annual apparent survival of blackbirds Turdus merula

Abstract

Summary 1.Fat reserves are stored energy that may help birds survive periods of harsh winter weather. This hypothesis predicts that annual apparent survival is higher for birds with large fat reserves than for birds with few or no fat reserves in winter. 2. Blackbirds ( Turdus merula Linnaeus) were ringed in central Italy from 16 November to 20 February during 1990February during -2001. Fat scores were recorded for each bird. We used these capture-mark-recapture data for 1703 blackbirds to estimate the effect of large fat reserves on annual apparent survival, while controlling for transients, using computer programs  and  . Probability of birds retaining large fat reserves, or retaining few fat reserves, over 2 successive years was also estimated. 3. Birds with large fat reserves did not have higher estimated annual apparent survival than birds with few fat reserves ( 2 large = 2 few = 0·595, SE = 0·043), inconsistent with our prediction. No effects of age, sex or year were detected on annual apparent survival. Birds with few fat reserves in any given year tended to have few fat reserves the following year ( -few → large = 0·332, SE = 0·052). Birds with large fat reserves in any given year were unlikely to have large fat reserves the next year ( -large → few = 0·585, SE = 0·080). 4. Large fat reserves may not increase annual survival of blackbirds wintering in central Italy. Winter weather in our study area may be too mild to effect survival. Alternatively, increased predation risk associated with large fat reserves may counteract any benefits of reduced starvation risk.

Assessing the role of body mass and sex on apparent adult survival in polygynous passerines: a case study of cetti's warblers in central Portugal

“…In practice, this approach works by constructing models in which survival over the interval immediately following the first (initial) capture (ϕ 1 ) differs from survival over subsequent intervals (ϕ 2 ). In addition, the ratio ϕ 1 /ϕ 2 can be used to estimate the resident probability of newly‐marked birds (ζ= ϕ 1 /ϕ 2 ) and its counterpart, the transient probability (1 −ζ) (Miller et al 2003). In the present study, the initial capture of first‐year birds (juveniles) were only possible during the autumn capture–recapture sessions, i.e.…”

“…Body mass, a proxy measure of individual fitness under selection pressure in bird populations (Covas et al 2002), is one example of such dynamic individual state variable that can be readily analysed in a multi‐state framework (Nichols et al 1992). To our knowledge, however, very few studies have modelled mark–recapture data with body mass used as a state variable (but see Miller et al 2003, McGowan et al 2011), despite the fact that national ringing scheme procedures usually incorporate the collection of mass data and/or fat scores at each capture–recapture of individual birds (EURING 2010).…”

Movement patterns and study area boundaries: influences on survival estimation in capture–mark–recapture studies

“…An important reason is the difficulty in distinguishing unavailability for capture from death in studies of population ecology. Evidence for this is the numerous studies that report estimates of apparent survival (φ) (the probability of survival given availability in the study area) rather than true survival (S) (Dinsmore and Collazo 2003, Miller et al 2003, Hagen et al 2005, Petty et al 2005, Sandercock et al 2005). Unavailability in the study area can result from physical absence (emigration from the study area) or presence in a state that renders the individual impossible to capture (e.g.…”

Fitness costs of parasites explain multiple life history tradeoffs in a wild mammal

“…There are several possible explanations for this observation: First, and most probably, anti-Tc IgA may in fact be more strongly correlated with another unmeasured component of individual quality than are strongyles or total IgA. For example, individuals with larger fat reserves may be able to sustain higher anti-Tc IgA levels (Demas et al ., 2003) as well as being fitter (Miller et al ., 2003; Milenkaya et al ., 2015). This possibility may reflect the confounding effects of individual quality in observational studies (van Noordwijk and de Jong, 1986).…”