Importance of hydrologic and landscape heterogeneity for restoring bank swallow (Riparia riparia) colonies along the Sacramento River, California

Published source details Moffatt K.C., Crone E.E., Holl K.D., Schlorff R.W. & Garrison B.A. (2005) Importance of hydrologic and landscape heterogeneity for restoring bank swallow (Riparia riparia) colonies along the Sacramento River, California. Restoration Ecology, 13, 391-402.
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Summary

Bank swallows have been extirpated as a breeding species from most of California (south-west USA), mainly due to the channelization of rivers and associated loss of ephemeral riverbank nesting areas. Potential impacts of three restoration measures were assessed: removing riprap (i.e. rubble/rock bank revetments); altering flow regimes; and restoring riparian vegetation.

A population model approach based on field evidence was used to predict effects of the restoration activities. Swallow distribution was monitored along a 160 km of the river from 1986-1992 and 1996-2003. The computer model tested whether site extinctions and colonizations corresponded with changes in maximum river discharge, surrounding vegetation cover and colony size.

A total of 283 bank swallow colony sites were monitored. Whilst colonization probabilities increased with maximum discharge, extinction probabilities increased. Thus whilst increased discharge increased creation of new bankside nesting areas, this also contributed to loss of some breeding sites through increased erosion. Restoring grassland near swallow colonies enhanced population viability. This was consistent with field observations as colonies tend to be located near to and birds tended to forage over, grasslands. Riprap is being allowed to erode at a few sites but removal is problematic due to potential subsequent land erosion; overall the effect of removing riprap could not be adequately quantified.

Note: If using or referring to this published study please read and quote the original paper, this can be viewed at: http://onlinelibrary.wiley.com/doi/10.1111/j.1526-100X.2005.00049.x/full