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SCIENCE BRIEF: Research indicates that restoring urban riparian habitats benefits non-breeding birds

Healthy riparian habitat is vital for Neotropical migrant and resident birds. It supports high biodiversity, and it is increasingly rare across landscapes. The total area of riparian habitat in California and Oregon has declined significantly in recent years and so have its associated bird populations. Human activity and other disturbances contribute to the loss of this scarce and essential bird habitat. Scientists, conservation practitioners, and land managers are collaborating to restore key riparian areas to health, and to understand how bird responses to restoration efforts can indicate restoration success.

lomakatsi logo (96 dpi)Since 1996, Lomakatsi Restoration Project (Lomakatsi) has worked in partnership with the Ashland School District to restore urban riparian habitat along Bear Creek at the Willow Wind Community Learning Center in Ashland, Oregon. In 2018, Klamath Bird Observatory (KBO) and Lomakatsi began to investigate how restoration efforts and changing vegetation structure might impact bird communities in Willow Wind’s urban riparian habitats.

Willow Wind riparian restoration site on Bear Creek in Ashland, Oregon
Figure 1: Willow Wind riparian restoration site on Bear Creek in Ashland, Oregon. Satellite images (on the left) show reference area (above dotted line) and restored area (bellow dotted line) with mist net locations (white bars). The top and bottom panels show habitat extent and condition before and after restoration.

In a recent research paper published in Northwestern Naturalist, KBO scientists used 17 years of mist-net capture data, which included 360 separate visits to operate the Willow Wind banding station, to measure the occurrence rates of several bird species on the property. Mist nets were placed in an area being restored by Lomakatsi, and in an adjacent reference area that received no restoration treatment during the years that data were collected (see Figure 1).

Abundance trends of seven wintering bird species in restored riparian habitats at Willow Wind
Figure 2: Abundance trends of seven wintering bird species in restored riparian habitats at Willow Wind. These local wintering populations benefited from the growth of willows and other native plants.

The results of the study indicate that restoration work in Willow Wind’s urban riparian habitats resulted in trade-offs for bird communities. Many bird species captured at Willow Wind during the non-breeding season had much higher capture rates in the restored area after restoration where their suitable habitat increased, including Purple Finch, Oregon Junco, Fox Sparrow, and more (see Figure 2). These same species did not increase over time, or increased less, in the unrestored area.

Yet other species had lower capture rates in restored areas. These species may have found the restored habitat less suitable over time. Common Yellowthroats, Red-winged Blackbirds, and Lincoln’s Sparrows were likely responding to a change in vegetation structure in the restored area as their preferred reed/cattail or open-field habitat was replaced by growing riparian plants. American and Lesser Goldfinches foraged heavily on invasive teasel, and as teasel was removed, they were captured less often in the restored area and the study site as a whole.

Restoration that supports birds during the non-breeding season is important for conservation. Birds are vulnerable during this time as they complete important, energetically taxing activities including dispersal, molt, migration stopover, and building reserves for the next breeding season. While the species shown in the Figure are found in riparian habitats during the non-breeding season, they breed and nest in western coniferous forests and more than 50% of western forest birds are in decline. Restoration work that supports bird populations during the non-breeding season, like the riparian restoration at Willow Wind, may also help bolster populations that breed in western forests and other habitats.

While some species benefitted from restoration and others did not, restoring vital riparian habitat is a bird conservation priority because so much of it has already been lost. According to lead author Sarah Rockwell, “Some trade-offs are inevitable when changing vegetation structure. It’s more about managers understanding their restoration goals, considering how individual species might respond, and balancing the needs of different species across the landscape.”