Differential Overnight Survival by Bumpus' House Sparrows: An Alternate Interpretation

Functional appraisal of the differential survival pattern reported by Bumpus (1899) for House Sparrows (Passer domesticus) prompted this study of morphometric and energy relations of birds collected at a winter roost in Ann Arbor. There was no relation between overall size (mass or Principal Component I score) and total body length of males, but PC-I scores and body mass were correlated significantly in Ann Arbor males and females. Female Ann Arbor sparrows had higher proportionate energy reserves than males and, overall, were predicted to have greater fasting endurance. When body masses of Bumpus' male and female birds were evaluated as a function of their PC-I scores (based on six skeletal measures), survivors of a given gender had the same slope but significantly lower elevation than non-survivors. The consistently higher body mass of non-survivors for a given PC-I score in Bumpus' sample suggests that these birds died of exposure soon after the storm's onset and, consequently, used far less of their energy stores than their surviving counterparts. If the birds classed as survivors by Bumpus were fully representative of House Sparrows enduring the storm of 1898, then larger males and intermediate-sized females were more likely to secure and remain at protected roost sites during the 1898 storm than their less fortunate roostmates. On the other hand, because Bumpus' sample was collected by hand and had a disproportionately low female composition, conclusions about gender differences in pattern of selection in Bumpus' birds must be questioned.