Blood sampling does not negatively affect apparent survival, recapture probability, or within-season site fidelity in Field Sparrows (Spizella pusilla)

Recent evidence suggests that blood sampling may negatively affect avian survival, which runs counter to the prevailing assumption that blood sampling, if performed properly, has little effect on survival in birds. Here, we take advantage of a long-term dataset (1986-2009) documenting the breeding biology of a population of Field Sparrows (Spizella pusilla) in northeastern Pennsylvania, USA, to assess the influence of blood sampling on sparrow survival. This study included 2 periods when blood sampling was not performed, interspersed with a period when blood was sampled. We examined the potential influence of blood sampling on annual apparent survival using Cormack-Jolly- Seber models in Program MARK. We also examined the influence of blood sampling on within-season site fidelity, as determined by whether birds remained on territory following collection of a blood sample. Our results suggest that apparent survival was actually higher for both sampled males and females in comparison to individuals captured during the same time interval but not sampled for blood. Further, apparent survival varied considerably over the years of the study (ranging from 0.27 to 0.59 in males and from 0.17 to 0.45 in females), and males consistently exhibited higher apparent survival than females. Finally, our results suggest that either (1) sampled birds had higher withinseason site fidelity (males) or (2) blood sampling did not affect site fidelity (females). Blood sampling in our population of Field Sparrows did not appear to have any measurable short- or long-term effects on survival.