Will Desert Purple Martins Use Our New Nestboxes?

By Olya Weekley

Desert Purple Martin pair, Ned Harris

The Desert Purple Martin (Progne subis hesperia) is a subspecies of Purple Martin whose breeding range spans the southwestern United States and northwestern Mexico. They nest in cavities created by woodpeckers in saguaros and cardons, both tall columnar cacti. However, invasion by non-native plants into the Sonoran Desert has led to unprecedented cactus-killing wildfires. Saguaros grow slowly and take 100–150 years to achieve the size necessary to host martin nests. As more of these cacti are lost to wildfires and human development, the lack of suitable nest cavities will become an even more limiting factor for the species’ population size. Unlike their eastern counterparts, Desert Purple Martins have not been documented to use nestboxes—a suitable design that meets the special needs of desert summer living would be a beneficial conservation tool.

Olya with all of the nestbox designs

In 2022, Tucson Audubon hosted a contest for nestbox designs that could mimic the temperature-buffering characteristics of saguaro cavities. We received 22 excellent plans: 19 in the adult category and three in the youth category. Each design was then evaluated by the Desert Purple Martin research team and a woodworking expert to assess dimensions, cost-effectiveness, ease of installation, and durability. Next, we placed the prototypes in the field to document the interior temperature of each compared to a nearby saguaro cavity. While it proved difficult to mimic the insulating qualities of the living flesh of a saguaro, three designs came the closest. Each of the winners received a cash honorarium for their accomplishment. While they all use different materials, there is one shared characteristic: the external part of the nestbox is separated from the inside chamber by inches of insulation.

In 2024 we put these three designs to the ultimate test: Purple Martin preference! We created 25 free-standing arrays, each consisting of the three nestbox designs affixed next to each other on a 16 foot post. Since the desert subspecies of Purple Martins is not known to use nestboxes, any species nesting in an artificial cavity would be an exciting discovery!

We did not document any Desert Purple Martin nests in our nestboxes, but we had several other cavity nesters use our boxes:

• 3 Cactus Wren nests
• 7 flycatcher nests
• 1 American Kestrel nest
• 2 roosting Western Screech-Owls

The secondary goal of the project, beyond martin use, is to create free-standing, temperature-buffering nesting structures to serve cavity nesting birds affected by increased competition due to saguaro-destroying wildfires and development. Seeing other cavity nesters successfully fledge from our boxes is incredibly encouraging.

We're looking forward to the 2025 season and hope to have martins using our nestboxes soon!

This work is made possible through the Wildlife Conservation Society’s Climate Adaptation Fund, the Disney Conservation Fund, Arizona Game and Fish, and private donations.

Olya Weekley is Applied Conservation Program Manager at Tucson Bird Alliance.