California crews left old telephone poles standing while restoring about 40 acres of land at Sierra Azul Open Space Preserve because purple martins use holes in the poles as nesting sites. The decision came as part of a wider restoration project in which more than 900,000 pounds of human debris was removed from the newly acquired properties.The Midpeninsula Regional Open Space District recently completed the restoration work on several properties that were added to the preserve. According to it, the land had abandoned vehicles, dilapidated structures and other debris accumulated over the years.While most of these remains were removed, the old telephone poles were kept. Midpen staff had discovered purple martins nesting in holes inside similar poles near the mountain top while working on Mount Umunhum.The discovery was significant because purple martins were thought to have disappeared from Santa Clara County. The western subspecies, Progne subis arboricola, prefers natural structures such as cavities in standing dead trees, known as snags. The birds found in Sierra Azul were using the old telephone poles in a similar way.
Purple martins’ nests
Purple martins are migratory birds that typically spend winters in South America before returning to North America in summer to breed. During these months, they need suitable nesting places as well as areas with flying insects for food.The western purple martin is different from the more common eastern variety in its choice of nesting sites. Eastern purple martins primarily rely on nest boxes supplied by humans, while the western subspecies prefers more natural cavities.Competition from nonnative European starlings for suitable nesting sites had led biologists to believe that the western purple martin was close to local extinction. Finding the birds nesting in Sierra Azul therefore led Midpen to begin efforts to support the population.The district started a multiyear programme to monitor the birds and test different nesting options. Its first attempt involved installing nest boxes, which had attracted purple martins in Oregon and Washington. However, the box-style design did not attract nesting birds in Sierra Azul.Midpen then designed a hollowed wooden pole that was intended to mimic the cavities found in natural structures. The design took into account the cavity dimensions, entrance-hole size and the height of the opening above the ground.The approach eventually showed results. In 2022, purple martins were confirmed nesting for the first time in the new Midpen-built structures. The finding supported the idea that western purple martins prefer more natural nesting habitats.
‘Ecological well-being of the land’
The restoration project also focused on clearing the wider landscape of human debris. Crews removed more than 900,000 pounds of material from the approximately 40 acres incorporated into Sierra Azul Open Space Preserve.Some of the waste required special handling. Teams removed and disposed of building materials containing lead and asbestos, along with old septic systems. This was done to protect restoration workers and prevent pollutants from entering the local watershed.After the debris was removed, specialists re-graded the land to resemble its natural, pre-development slopes. This was intended to restore the area’s original drainage patterns.The final stage involved hand-seeding the land and spreading weed-free straw to support the return of native chaparral and forest.“Our goal is to work in a way that supports the ecological well-being of the land,” said Midpen Capital Project Manager Ayden Sabharwal.The restoration is also connected to the planned Umunhum-to-the-Sea regional trail. The properties are located along the future trail corridor.Meanwhile, Midpen plans to continue monitoring the purple martins and work with partner agencies to share expertise on habitat improvements.
