Burrow occupancy and nesting phenology of bank swallows along the Sacramento River (original) (raw)

The bank swallow (Riparia riparia), a threatened species in California, has been monitored along the Sacramento River since 1986. Annual counts of burrows and past data on the rate of burrow occupancy have been used to estimate the number of nesting pairs of bank swallows. However, the burrow occupancy figure in use (45 percent of burrows occupied) has not been updated for nearly 20 years. We conducted surveys of burrow occupancy at nine bank swallow colonies along the Sacramento River during and after the breeding season of 2010. We tracked changes in colony extent and number of burrows and made observations of burrow contents. Burrow counts increased through the latter half of June and then remained relatively constant through early August. Eggs and young were observed from the beginning of the study on April 26 through early July, but eggs were common only through June. Nests with eggs peaked in early May and again in the third week of June; nests with chicks were highest in late...

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