MAKING CONSERVATION CONNECTIONS: DESERT PURPLE MARTINS AND SAGUAROS

By Aya Pickett

Desert Purple Martin on saguaro, Scott Olmstead

Illuminated by headlights, we do our best to quickly and quietly set up our first net. Dawn is breaking, signaling the best time for us to begin our research efforts.

We are surrounded by a vast tract of Sonoran Desert as far as the eye can see. Prickly pear, cholla, and creosote are at our level, but above us towers a saguaro: a giant, columnar cactus at least 40 feet tall with six massive spiny arms. A few soup-can-sized holes have been carefully carved into its sides. These cavities, originally created by woodpeckers, are found only on saguaros that are at least 13 feet tall.

Many species use these cavities after the woodpeckers depart, most notably, our study subspecies, the Desert Purple Martin. These martins are assumed to have high site fidelity, meaning they will use the same nest cavity year after year. Active nests can be found in and around Tucson in areas such as Tucson Mountain Park, the Mason Center, and Saguaro National Park. Our records show that they nest almost exclusively in cavities that are more than 15 feet off the ground and therefore have a strong reliance on mature saguaros. One of the most important facts we know about this understudied subspecies is that without saguaros, their nesting habitat would become extremely limited, and their populations would drastically decline. As our climate changes and saguaros are pressured with increasing drought, freezes, and fire, Desert Martins will be affected.

Purple Martin in saguaro nest cavity, Richard Fray

Making a conservation plan for a species often starts with gaining an understanding of its complete life history. For example, where do they go during the winter? What is their migration pathway? Should they be classified as a subspecies or a species? When it comes to Desert Martins, these basic facts are unknown. Tucson Audubon’s Desert Purple Martin Project seeks to answer these questions.

The project’s primary tasks in the summer of 2022 are to capture Desert Purple Martins, collect samples, and attach geolocators. We start by setting up a finely meshed, black mist net used to safely capture small birds. The net is held up by two 30-foot poles (about the height of a two story house!) on either side that keep the net taut. By having this tall net, we can place it just outside of an active martin nest cavity, giving us a higher probability of capture. Under normal circumstances, in front of dense vegetation, the net is nearly invisible to a flying bird, but with a sky-blue background the net is easily seen. As soon as the net is set up, the martins flock to it, zipping around and making alarm calls as they circle this strange, new object. In all of the commotion, one of the martins flies into the net and we quickly lower it and place the martin into a soft cloth bag that we use to transport it to our banding table. Most of the martins, however, handily avoid the net.

Left: Joe Siegrist of the Purple Martin Conservation Association installs a geolocator on a male Desert Martin. Right: Project participants hold mist nets up near a colony saguaro with multiple martin
nests while tagging in 2022, both by Jonathan Horst

At the banding table, we collect morphometric data and two feathers that will be used for genetic testing and an ecotoxicology study. These samples will be used by researchers at Northern Arizona University (NAU) who are looking at the impacts of pesticides on martins throughout their life cycle. We are also beginning to work with NAU and the University of Arizona on genetic analysis of the three Purple Martin subspecies. Finally, we attach the geolocator to the bird. A thin piece of twine gets looped around the upper part of each leg so the bird is wearing it on its back like a little backpack. This tiny device, weighing less than a nickel, records daylight information that determines its location. From capture to backpack attachment, the whole process takes less than ten minutes. By deploying these devices on birds, we hope to be able to discover their flight routes and where they go during winter.

After we are done, we place the bird on one open hand and allow it to fly off on its own. As the bird leaves, it gives a few shakes in mid-air to adjust to its new apparel. Since the geolocators don’t have any wireless data transmission abilities, we will need to recapture the same bird once it returns next summer. I look forward to coming back next year and hope the martin will return to its home inside the same saguaro.

Learn more about Tucson Audubon's Desert Purple Martin Project.

Aya Pickett is the Restoration Project Manager at Tucson Audubon.