Colony site selection in bank swallows
Hjertaas, Dale G.
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Bank Swallow colony site selection was studied on a 6,129 hectare area in the Qu'Appelle Valley near Fort Qu'Appelle, Saskatchewan. Comparison of 60 banks used by Bank Swallows with the 349 unused sites showed that taller, vertical, more recently excavated sites with sand or fine gravel soils and no obstructions in front of the bank were selected. Colony size, which ranged from 1 to 48 pair with a mean of 7.7 pair, was not significantly correlated with any bank character. Mean clutch size was 5.0. In successful nests 90.5% of eggs fledged. Probability of a nest surviving from laying through fledging was 63.4%. Nest success was only correlated with tunnel depth and date of initiation, although additional data suggest bank characters are also important. Tunnel nesting gives Bank Swallows significant advantages and forces clustering on a restricted habitat base. Suitable habitat is left vacant, however, indicating that Bank Swallows probably derive additional advantages from associating with conspecifics.