Using ring-recovery and within-season recapture data to estimate fecundity and population growth.

Tag-recovery data from organisms captured and marked post breeding are commonly used to estimate juvenile and adult survival. If annual fecundity could also be estimated, tagging studies such as European and North American bird-ringing schemes could provide all parameters needed to estimate population growth. I modified existing tag-recovery models to allow estimation of annual fecundity using age composition and recapture probabilities obtained during routine banding operations of northern pintails () and dark-eyed juncos (), and I conducted simulations to assess estimator performance in relation to sample size. For pintails, population growth rate from band-recovery data (λ = 0.93, : 0.06) was similar but less precise than count-based estimates from the Waterfowl Breeding Pair and Habitat Survey (λ: 0.945, : 0.001). Models with temporal variation in vital rates indicated that annual population growth in pintails was driven primarily by variation in fecundity. Juncos had lower survival but greater fecundity, and their estimated population growth rate (λ: 1.01, : 0.19) was consistent with count-based surveys (λ: 0.986). Simulations indicated that reliable (CV < 0.10) estimates of fecundity could be obtained with >1,000 within-season live encounters. Although precision of survival estimates depended primarily on numbers of adult recoveries, estimates of fecundity and population growth were most sensitive to total number of live encounters. Large-scale ring-recovery programs could be used to estimate annual fecundity in many species of birds, but the approach requires better data curation, including accurate assessment of age, better reporting of banding totals, and greater emphasis on obtaining and reporting within-season live encounters.