Point Reyes Bird Observatory, Observer 108

The Unbalance of Nature:  Songbirds in the Mount Vision Fire Zone

By Geoffrey Geupel
One year ago, on October 10, 1995- within hours of containment of the massive Mount Vision fire - PRBO biologists donned bright yellow fire suits and hard hats and paid our first post-fire visit to the once lush riparian valleys of Point Reyes National Seashore.

In fly-overs at an altitude of 1000 feet, fire assessment team members had reported that most riparian areas in the burn appeared relatively unscathed. Our on-the-ground visits were some of the first to relay that the understory, the most important habitat for breeding songbirds, was devastated: many stretches in Muddy Hollow and Coast Camp were over 90% burned.

The promise of regeneration, however, was present in the form of small patches of riparian habitat that had miraculously escaped the flames. Because the wind-fanned flames had moved extremely rapidly, burning some 9000 acres in just 24 hours on the second day of the fire, they burned different areas at different intensities. This left a mosaic on the land that included some relatively small unburned riparian patches. During the blaze, these had acted as refugia for numerous creatures, especially mobile ones like songbirds.

In the weeks immediately after the fire, these patches were literally inundated with birds. Birds of all types persisted in them: Wrentits and White-crowned Sparrows from the coastal scrub; nuthatches and woodpeckers from the bishop pine forests; and even yellowthroats and Marsh Wrens from nearby burned marshes. Our data from bird censuses and regular mist-netting backed up our first impressions: the abundance and diversity of birds in these riparian patches in the months following the fire were higher than in nearby watersheds outside the burn area.

A general consensus among ornithologists, though, was that the fire's real impact would occur this spring, when the breeding season began. During the nesting cycle, selective pressures exert a powerful force on most landbirds. For species that build open-cup nests, the average rate of nest success across North America is only 42%. When birds attempt nesting in degraded or disturbed habitats, their success drops to less than 20%: fewer than two out of ten nests attempted will fledge young, and this is too low a success rate to maintain a stable population.

A Wilson's Warbler feeding young in the nest
A Wilson's Warbler feeds young in its nest on the Point Reyes National Seashore.

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