While walking along the Anza Trail near Tubac you may have seen a row of very small nestboxes or birdhouses mounted in the trees. Tucson Audubon is undertaking a two year investigation on what nestbox design is preferred by Lucy’s Warblers. This tiny pearl-gray warbler with a dark eye is one of only two cavity nesting warblers in the US. They are closely tied to mesquite trees, often seen hunting for tiny insect prey and nesting in these trees. They look for a woodpecker hole or bark crevice to build their nest but these features are often found in old, large mesquites. Large mesquite trees are often removed for their valuable wood so sometimes all that remains are smaller trees. Several small trees may provide a pair of Lucy’s Warblers with all the insects they need but lack a cavity for them to build their nest. Could a nestbox be the solution to this problem and make smaller mesquite trees suitable for nesting?
Lucy's Warbler with Nest Materials. Image: Lois Manowitz, used with permission
Lucy's Warbler in Nest Cavity. Image: Scott Olmstead, used with permission
Lucy's Warbler nest in Sabino Canyon Dam. Image: Mark Hengesbaugh, used with permission
In 2018, a new arrangement of nest boxes was installed in trees. Image: Michael Dunn, used with permission
To find out what these tiny birds are looking for in a nestbox Tucson Audubon set up groups of different types of boxes in multiple areas for the birds to find and hopefully explore. Volunteers will be checking these boxes weekly to see if any Lucy’s Warblers have decided to use any of these boxes. This is the first time that anyone has tried to develop nestboxes for this species. Sixty each of the five different designs of Lucy’s Warbler nestboxes were built in the winter/early spring of 2017 and then all 300 nestboxes were installed in three different locations: Anza trail alone the Santa Cruz River in Tubac (south of Tucson), along the Tanque Verde Wash in east Tucson and in the 7B ranch near the San Pedro River in Mammoth, AZ (north of Tucson). Each of the three study sites has 20 points where one of each of the five different boxes is placed in a random order. Of the 300 nestboxes installed in 2017 only three were used by Lucy’s Warblers. So Tucson Audubon went back to the drawing board and created new designs. The new boxes have been added to the original 60 locations, 20 of which are along the Anza Trail. Check them out next time you travel the trail!
A row of wooden box nests in a mesquite tree. Image: Michael Dunn, used with permission
This work was made possible by a grant from the Tracey Aviary Conservation Fund and supported by Tucson Audubon’s Bringing Birds Home program.
Learn more about the Anza Trail in Santa Cruz County on our interactive map or the Anza Trail Coalition of Arizona.