Ecological restoration works for urban birds in San Francisco’s Presidio
October 27, 2021
This blog was written by Tom Gardali with contributions from Point Blue staff Mark Dettling, Kristy Dybala, and Diana Humple and Presidio Trust staff Brett Stevenson, Lewis Stringer, and Jonathan Young
Restoring lost or degraded ecosystems has emerged as one of our most powerful tools to arrest the loss of biodiversity, combat climate change, and improve overall human health and well-being. In fact, the year 2021 marks the start of the United Nations Decade on Ecosystem Restoration, which is a coordinated “global rallying cry to heal our planet,” and Point Blue has crafted a declaration of commitments to support the global effort.
While cities and towns have not historically been considered priorities for ecological restoration projects, the UN Decade effort explicitly calls for urban restoration. The Presidio Trust, the National Park Service, and the Golden Gate National Parks Conservancy were visionary in their pursuit of restoration in San Francisco’s Presidio, and since 2001 they have restored 78 acres.
Some might question the value of doing restoration in urban areas given that cities have been massively transformed, are human dominated, and represent a tiny percent of the Earth’s total surface area. However, there are many reasons for prioritizing restoration in urban areas – and the benefits often go beyond the vegetation and wildlife being restored.
For example, ecological restoration is considered a public health intervention because it frequently provides relatively easy access to natural areas which can increase individual and community health – both physical and psychological (see here for example and references therein). Further, the actual act of doing the restoration (e.g., prepping, planting, weeding, watering, etc.) can improve an individual’s mind, body, and spirit in ways other activities may not be able to (termed restorative recreation). The restoration work in the Presidio has largely been implemented by volunteers (approximately 160,000 volunteer hours to date) and hence these volunteers may have benefited in mind, body, and spirit.
Despite growing evidence and momentum around the importance of urban restoration for human health, little information exists on wildlife response in urban settings. In close collaboration with the Presidio Trust, and to provide the Presidio Trust with information they need to assess the effects of their restoration work, Point Blue Conservation Science has studied, and continues to study, bird response to habitat restoration in the Presidio. There are many important reasons for understanding bird response to restoration and these include:
- Birds are declining across North America. A recent analysis shows widespread declines of birds in North America since 1970 resulting in the loss of nearly three billion individuals from a wide variety of species, including those once considered common.
- Birds are recognized as indicators of ecological integrity, with many responding very quickly to changing vegetation following a restoration, so their presence and abundance provides information on the restoration’s efficacy.
- Birds provide a wide variety of ecosystem services, including devouring pests, pollinating flowers, dispersing seeds, scavenging carrion, cycling nutrients, and modifying the environment in ways that benefit other species.
- Birds are highly visible with a great deal of public interest attracting many bird watchers to the Presidio and delighting regular visitors and residents. Their songs and behavior (e.g., long distance migration) also inspire great interest. Bird watching can also have significant positive impacts on local to national economies.
We systematically surveyed birds at select Presidio restoration sites from 2010 to 2021 to assess the success of restoration in increasing bird populations. Each site was surveyed during both the breeding and winter seasons starting ~1 year after the restoration was completed and then again at 3, 5 and 10 years post restoration. We focused our analysis on a set of 16 focal species at 16 riparian and coastal scrub restoration sites. The focal species were selected because they rely on riparian and coastal scrub vegetation and their life history characteristics collectively represent different aspects of a healthy system. We analyzed the average change in abundance of each focal species across all 16 restoration sites combined over 10 years post restoration.
Of the 16 focal species examined, fully 80% were increasing or stable; 8 of them were increasing with time since restoration, 5 were stable with no detectable change, and 2 were decreasing.
Stable or increasing species had a range of life-history characteristics – for example, there were cavity nesters like the Chestnut-backed Chickadee and shrub nesters like the Song Sparrow. The diversity of life-history traits of the increasing and stable groups suggest that the restorations in the Presidio are successful at providing a range of needs for the bird community. It is also important to highlight that stable populations, those with no detectable changes, represent signs of success. We are not sure why House Finch and White-crowned Sparrow declined, but note that White-crowned Sparrows are declining throughout their range. Additionally, both species tend to favor open weedy habitat during winter when they also flock (versus holding territories), and hence it is possible that restoration resulted in a localized reduction in weedy areas (e.g., a weedy field edge restored to dense riparian forest). More information on the abundance and distribution of these two species Presidio wide could help contextualize these results and determine if special management actions are needed. Understanding long-term population trends, relative to environmental contexts such as restoration, informs adaptive management and guides the ongoing conservation of these urban birds.
Our results clearly show a positive effect of urban restoration on the bird community, and hence results demonstrate that, along with the multiple-benefits related to human health and well-being, habitat restoration in San Francisco’s Presidio is a good investment.
For more information about this study, please contact Diana Humple at firstname.lastname@example.org.