The Isleta Reach is a 48-mile stretch of the Rio Grande south of Albuquerque that runs through the heart of some of New Mexico’s richest farmland. However, if you were on a canoe paddling down the Isleta Reach, you may think you’re in a remote wilderness somewhere in the backcountry.

Even as communities like Los Lunas and Belen continue to expand, the river feels as wild as ever. Cottonwoods tower over the river, 50 feet into the air. Willows along the bars sway in the seemingly perpetual breeze, and bird songs echo throughout the verdant summer bosque. However, some summers are more brutal than others. In recent years, we’ve been seeing more summers where stretches of the Isleta reach dry up, and according to climate models, that may be more and more common in the decades to come.

To mitigate the effects of increased drying on the river, the Middle Rio Grande Conservancy District (MRGCD) has initiated a pilot program over the last four years, the “Environmental Water Leasing Program.” Local farmers have the opportunity to enroll in the program and let their field go fallow for the year. This “break year” has many benefits; fallowing gives the soil a break to recover, improving its long-term resiliency; fallowing allows for a better water supply for active farmers during a given year. MRGCD compensates the farmer for their participation and diverts their water back to the river in a strategic location to combat drying during the dog days of summer. Additionally, Audubon Southwest has been leasing water from the local municipalities of Bernalillo, Los Lonas, and Belen. This leased water has been used to augment these MRGCD flows for these strategic locations in the Isleta Reach. We call these strategic locations “outfalls”, and they are proving to be invaluable features of the Middle Rio Grande. To make the most of these outfalls, MRGCD, Audubon Southwest, and other conservation partners have been investigating ways to enhance the function of these sites.

For the past 5 years, Audubon Southwest and our friends at the Bird Alliance of Central New Mexico have been documenting the breeding bird communities at these outfalls. We wanted to know how birds were using the bosque habitat along these outfalls. Each summer, volunteers walk line transects that run parallel to 6 select outfalls in the Isleta reach (check out the map below). As they slowly walk along the outfall, they listen to the cacophony of birds and parse out which species are present. They record the number of each species they detect, which requires great patience, careful listening, and a sincere love for birds. Volunteers do this 3 times throughout the breeding season at each outfall to capture the bird community.

In 5 years, our volunteers have counted a total of 9,054 birds of 124 different species! The 20 most abundant birds along the outfalls are found in the orange table to the right. If you’re walking through the bosque in June, you’re almost guaranteed to hear a Yellow-breasted Chat calling from the willows, spot a Spotted Towhee scratching at the ground, and get buzzed by a hungry Black-chinned Hummingbird in search of some flowers. Some of these birds, like Common Yellowthroats, Lucy’s Warblers, and Summer Tanagers can ONLY be found breeding alongside rivers/ wetlands - we call these birds “riparian obligates.” They are our true indicator species when considering bosque management. Species like Spotted Towhees, Mourning Doves, and Lesser Goldfinches can breed in a variety of habitats from pinyon-juniper woodlands to desert grasslands, which New Mexico has an abundance of. In contrast, dynamic riparian habitat with reliable water is in low supply in New Mexico – which makes the Rio Grande such a critical area for riparian birds. Therefore, the quality of bosque habitat should be judged not on the total number of birds present, but by the abundance and diversity of riparian obligates present.

Now let’s take a closer look at the riparian birds and see how they are distributed among the outfalls. We have omitted a few riparian specialists from our analyses, like Bell’s Vireos, Bullock’s Orioles, Willow Flycatchers, and Yellow Warblers due to low detection rates. Results from our surveys reveal that riparian obligates were not evenly distributed across the sites – see the bar chart below. From this analysis, we can see that Storey, LP2, and San Francisco are supporting significantly more riparian birds compared to other outfalls.

So why are riparian birds more abundant at Storey, LP2, and San Francisco? We are actively monitoring riparian conditions at each of the outfall sites to relate vegetation to bird abundance. Our preliminary assessments have provided some context and hypotheses that will guide us forward into the next 5 years of monitoring these outfall sites. For example, New Belen supports the fewest riparian obligates compared to other outfall sites and we believe that is because of the lack of a well-established understory or midstory at New Belen. Many riparian obligates, like Blue Grosbeaks, Common Yellowthroats, Gray Catbirds, and Yellow-breasted Chats prefer bosque with a dense midstory. Midstories in the MRG are often comprised of New Mexico olive or Russian Olive, both of which provide shelter and food for birds. They may also serve as a thermal refuge during the hottest days of the breeding season. On the other hand, the lack of a dense midstory at New Belen may be the reason why we observe a relatively high abundance of Summer Tanagers at the site. Previous bird habitat studies by Perry et al have found that Summer Tanagers prefer this type of open forest structure in the west because of their propensity to capture bees and wasps on the wing, commonly called “hawking” or “sallying”. An open forest structure provides better conditions for spotting and capturing insects in this manner.

The San Francisco outfall is positioned near the southern end of the Isleta reach, where the Rio Puerco meets the Rio Grande. Over the past couple years, the pilot program has worked to restore the San Francisco outfall. The channel was dredged, miniature floodplain widened, and flow deflectors installed to induce meandering – all of which increases the functionality of the outfall and provides critical habitat for the endangered Rio Grande Silvery Minnow. The next step in the restoration plan is to plant native trees and shrubs along the bank of the outfall that will provide new bird habitat. Therefore, the next five years of data should provide some insights into the efficacy of those restoration efforts.

Southwestern Willow Flycatchers, an endangered bird species, have been increasing in the Isleta Reach over the past few years. These small, inconspicuous birds thrive in decadent willow thickets where the humidity is high and the bugs are plenty. If the willow thicket is flooded – even better! As vegetated bars and islands have matured throughout the reach, suitable breeding habitat has opened up for Southwestern Willow Flycatchers.

The first five years of data have provided us with a snapshot of the bird community and what we can expect to find along the outfalls. In the coming years, we will continue to monitor the bird communities at these sites, and expand our efforts to include a 7th outfall site – the Peralta outfall. MRGCD is in the process of installing an Outfall Control Structure at the Peralta site, so that they may make strategic water deliveries during the summer months. The bosque surrounding the Peralta outfall burned in 2022, completely altering the vegetation community, so we’re curious to see how birds will recover at this site. We are also adding a new aspect to our bird surveys. In addition to identifying and counting the birds along the outfall, volunteers will map the approximate location of each bird. Through this effort, we will be able to refine our understanding of breeding bird habitat-use in the bosque and leverage those insights to help guide bosque management decisions that support healthy bird populations.

If you’ve never visited an outfall in the Isleta reach, I strongly encourage you to check one out. They’re great birding trails that are a bit off of the beaten path. If you are interested in joining our team of volunteers, reach out to Tucker Davidson: tucker.davidson@audubon.org. Let’s Go Birding Together!