Importance of a Low Talus in Location of Bank Swallow (Riparia Riparia) Colonies

Article excerpt

ABSTRACT.-After several years of disuse, bank slumping in a large (395.6 rn circumference), roughly circular sand pit had raised the talus to a depth of 2.0 m, reaching to within 0.5 to 0.7 m of the overlying sod. No bank swallows (Riparia riparia) were nesting in this sand pit. Two truckloads of this readily-scooped talus were removed in 1995, creating separate stretches (each about 11 m) in which a shallow new talus (<0.5 m) left 2.0 m to 2.2 rn of exposed, vertical bank. In the spring of 1996, bank swallows established colonies in each of these newly exposed stretches and nowhere else. A "roulette wheel" probability model is presented from which the probability that these low talus stretches were selected as colony sites by chance is 0.001.

INTRODUCTION

John (1991) found in his Canadian study area (45'35'N, 79'23'W), sands that were too soft and too prone to crumble permitted only short-lived colonies of bank swallows (Riparia riparia), and were avoided where a resulting high talus allowed "easier access to terrestrial predators." No statistical tests of the use of low talus banks, or avoidance of high talus banks, by bank swallows, were reported by John (1991) or, to my knowledge, by other workers.

An opportunity to test these associations was afforded at Scarlett's sand pit, near Sundridge, Ont., Canada (44'35'N, 79'23'W) in 1996. This shallow sand pit had not been mined for several years, and around most of its perimeter the talus had accumulated to within 0. …