Feeding trial evaluation of supplemental sodium and calcium use by pigeons

Abstract

AbstractThe Pacific Coast band‐tailed pigeon's (Patagioenas fasciata monilis) conspicuous and well documented use of supplemental minerals has allowed wildlife managers to conduct counts of pigeons at sites with minerals to index their abundance; but despite at least 9 associated peer‐reviewed research publications since 1998, the reason that band‐tailed pigeons use mineral sites and necessity of that use remains unknown. I conducted feeding trials with pigeons during summers of 2009 and 2010 to evaluate maintenance and reproductive performance associated with access to supplemental minerals: one with 24 pairs of wild‐caught band‐tailed pigeons, and one with 30 pairs of wild‐caught rock pigeons (Columba livia). Data indicate that red elderberry (Sambucus racemosa var. arborescens) and cascara (Rhamnus purshiana) berries (natural food items) are high energy food sources for band‐tailed pigeons, and that band‐tailed pigeons can thrive on these berries without access to supplemental sodium and calcium. However, access to supplemental sodium could offer band‐tailed pigeons advantages in body weight maintenance or gain when consuming a diet low in sodium and high in potassium. Band‐tailed pigeons did not nest in this study; thus, it remains unknown if there are benefits to reproductive performance from access to supplemental minerals. Rock pigeons with access to supplemental sodium fledged ≥33% more young than those pigeons without access to supplemental sodium, and this was primarily associated with the increased number of clutches and increased fledging rate. Also, fledgling mass was greater ( ± SE = 35.5 ± 7.9 g, 95% CI = 19.3–51.8) for rock pigeons with access to supplemental sodium at fledging in 2010, but the difference was not statistically significant in 2009 (5.9 ± 22.9, 95% CI = − 43.2–55.0) possibly because of the nutritionally limited diet that year. Access to supplemental sodium could offer band‐tailed pigeons advantages in fecundity and hatchling survival rates (recruitment) through increased efficiency in food conversion. Natural mineral sites used by band‐tailed pigeons should be conserved until additional information is available for evaluation. Also, comparison of counts of band‐tailed pigeons at mineral sites over time and among sites must be interpreted cautiously until the factors (e.g., diet, weather, accessibility, supplemental mineral concentration, etc.) that influence the proportion of the local band‐tailed pigeon population that uses mineral sites can be determined.