Colima Warbler Census – 2022 Report
By James J. & Lynne M. Weber
Abstract
During the May 14 – 15, 2022 census of Colima Warblers (Leiothlypis crissalis) in the Chisos Mountains of Big Bend National Park, a total of 36 warbler territories were observed. Over a two-day period 42 volunteers surveyed the original ten count areas established in the first census (Wauer, 1967) and all six additional count areas used in subsequent surveys (Table 1). The total number of warbler territories by count area over the fourteen surveys conducted to date is found in Table 2. The objective of the census was to monitor population stability for this highly localized American visitor.
Figure 1. Colima Warbler (Leiothlypis crissalis). A beautiful Colima Warbler, photo taken by Jim Weber on 5/3/2012 in Boot Canyon, Big Bend National Park.
Background
Colima Warblers are a species of special interest as their range extends only marginally into the United States in the Chisos Mountains of Big Bend National Park (Figure 2) and possibly the Davis Mountains in southwest Texas. A stable warbler population may be an indication of the continued health of the overall Chisos Mountains ecosystem. Bird enthusiasts from all over the United States and from other countries travel to Big Bend to make the arduous hike up into the Chisos Mountains in search of this unique species.
Figure 2. The Chisos Mountains in Big Bend National Park. Yellow borders mark prime warbler habitat covered by the count areas. The shaded area marks the closed section of the East Rim count area that was included in the 2022 census. All topographic maps were created using National Geographic’s Big Bend National Park Explorer 3D software, copyright 2007.
The adult Colima Warbler (Figure 1) has a grey face with white eye-ring. A pale rufous crown patch is usually concealed. Crown and upperparts are grey-brown, tinged olive, with bright olive-yellow rump and upper tail coverts. The throat and under parts are grey, washed with buff brown on flanks. Undertail coverts are ochre-yellow and the chest is washed buff in fresh plumage. The plumages of the sexes are similar (Howell and Webb). Detecting these birds in rugged country is easiest by listening for the singing males. They start arriving in the park by mid-March and are detectable on territory by early to mid-April.
The call note is a metallic tchiu or chink, fuller than a Virginia’s Warbler. The song suggests an Orange-crowned Warbler or sometimes even a Bewick’s Wren, a rising, trilled series of chips, one to two seconds in duration, and ending fairly abruptly with soft warbled notes, sisisisisisisisiiriu. At times it may end with a few separate chips, siiiiiiiiiiiir swee-twee-twee-twee, etc. (Howell and Webb). The breeding range extends from the Chisos Mountains of southwest Texas, south in Sierra Madre Oriental of Mexico through central Coahuila to southwest Tamaulipas, northeast Zacatecas, and north San Luis Potosi between 1500 and 2500m (Beason and Wauer). Nesting occurs on the ground in leaf litter or under clumps of grass. This warbler winters in Mexico from September to April at 1500 to 3500m from southeast Sinaloa and southwest Durango south along the Pacific slope to southern Jalisco and east to Distrito Federal and Morelos. It can also winter along Pacific slope of western and central Guerrero and rarely south to northern Oaxaca (Beason and Wauer). A complete natural history of the Colima Warbler may be found in the Beason and Wauer report (1998).
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| Colima Warbler range map. Source: www.whatbird.com |
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| Typical Colima Warbler habitat. Photo taken by Jim Weber on May 3, 2012 in Boot Canyon, Big Bend National Park. |
Census Procedures and Count Areas
The 2022 census procedure and count areas covered (Table 1) were consistent with those used in the inaugural 1967 census and subsequent censuses in 1968, 1969, 1970, 1974, 1976, 1982, 1984, 1996, 2000, 2005, 2010, and 2015. Teams of two to seven volunteers surveyed each count area on May 14th and 15th, recording the locations of Colima Warblers heard or seen on topographic maps and datasheets (see Appendices).
# | Count Area | Description | Volunteer Assignments |
1 | Emory Peak Trail (1b) & Upper Pinnacles Trail (1a) | Includes the upper portion of the Pinnacles Trail on the north side of Emory Peak, as well as the eastern ridge (Emory Peak Trail) route to the summit. Elevations vary from 6600 to 7800 ft (2012 to 2377m). | Emory: T. Clark, S. Berg, D. Morgan, J. Hull Upper Pinnacles: J. Reidy, R. Cartwright, V. Owen, J. Owen |
2 | Toll Mountain (2a) & Kibbe Spring (2b) | Includes the upper slopes of the south and southwest-facing corner of the Chisos Basin to the western ridge of Toll Mountain (Kibbe Spring (2b) not covered). Elevations vary from 6800 to 7400 ft (2072 to 2256m). | D. Proppe, K. O’Keefe, A. Balogh
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3 | East Rim Canyons | Includes several short canyons east of Boot Canyon between Juniper Canyon and the East Rim. Elevations vary from 7000 to 7400 ft (2134 to 2256m). | T. Clark, S. Berg, D. Morgan, J. Hull |
4 | South Rim Trail (4b) & Upper Blue Creek/West Colima Trail (4a) | Extends from near Laguna Meadow and upper Blue Creek Canyon to the Colima Trail pass and to the South Rim. Elevations vary from 4600 to 7400 ft (1402 to 2256m). | South Rim: K. Perez, S. Ott, L. Black, D. Macedo, S. Rudokas, M. Luschen Blue Creek/West Colima: J. Chenoweth, B. Reiner |
5 | Upper Boot Canyon | Extends from the East Rim Trail junction to the South Rim. Elevations vary from 7000 to 7200 ft (2134 to 2195m). | N. Sandoval, K. Meisenhelder |
6 | Middle Boot Canyon (6b), Upper Juniper Canyon (6c), & East Colima Trail (6a) | The heart of the Chisos Mountains. Includes Boot Canyon from the cabin to the East Rim Trail fork, as well as the side-canyons that run northwest from the cabin (along the east slope of the Colima Trail) and two adjacent side canyons. Elevations vary from 6800 to 7300 ft (2073 to 2225m). | Middle Boot/Upper Juniper: J. Scalise, C. McCann, A. Stewart, L. Moulton East Colima: K. Perez, S. Ott, L. Black, D. Macedo, S. Rudokas, M. Luschen |
7 | Lower Boot Canyon | Runs from the cabin down-canyon to the Boot Canyon pour-off and side canyons. Elevations vary from 5400 to 6800 ft (1646 to 2012m). | N. Sandoval, K. Meisenhelder |
8 | North Boot Canyon | Begins just below the western ridge of Toll Mountain and empties into Lower Boot Canyon. Elevations vary from 5400 to 7000 ft (1646 to 2134m). | D. Proppe, K. O’Keefe, A. Balogh |
9 | Laguna Meadow Canyons | Includes the Laguna Meadow Trail proper as well as several associated canyons, including the upper reaches of Cattail Canyon. Elevations vary from 5600 to 6600 ft (1707 to 2012m). | J. Chenoweth, B. Reiner |
10 | Lost Mine/ Upper Pine Canyon | The upper portions of the Lost Mine Trail and upper Pine Canyon, including the drainage that can be reached from near the end of the Lost Mine Trail. Elevations vary from 6300 to 6900 ft (1920 to 2103m). | T. Vandenberg, E. Huryn, C. Hoyt, C. Negele |
11 | Middle Pine Canyon | The traditional Pine Canyon Trail that lies below the pour-off at the end of the trail, accessible from the Glenn Springs and Pine Canyon Roads. Elevations vary from 5400 to 6900 ft (1646 to 2103m). | P. Fushille, A. Gosselin, J. Kuhl, S. Kuhl, H. Kuhl, A. Kuhl, L. Scoggins |
12 | Campground Canyon | A steep and narrow canyon situated on the south slope of Pulliam Ridge, across from the Basin Campground. Elevations vary from 5200 to 6600 ft (1585 to 2012m). | J. Weber, L. Weber |
13 | Upper Green Gulch | Includes the steep northwest-facing slope in Green Gulch. Elevations vary from 5700 to 6000 ft (1737 to 1829m). | R. Swanson, C. Ledezma |
14 | Middle Green Gulch | Includes the dual canyons on the steep northwest-facing slopes of Lost Mine Peak, visible from the Green Gulch Road. This area is accessible from either Green Gulch or from the top of the switchback of the Lost Mine Trail. Elevations vary from 5800 to 7000 ft (1768 to 2134 m). | N. Durish, T. Athens |
15 | Lower Green Gulch | Includes a single, northwest-facing canyon on the lower northwestern flank of Lost Mine Peak, accessible from the Green Gulch Road near the top of Pulliam Ridge. Elevations vary from 5000 to 5600 ft (1524 to 1707m). | N. Durish, T. Athens, R. Swanson |
16 | Maple Canyon | Drains the southeastern corner of Pulliam Ridge, accessed by trail from a pull-out along Green Gulch Road. Elevations vary from 5200 to 5400 ft (1585 to 1646m). | J. Weber, L. Weber |
Table 1. 2022 Census Count Areas and Volunteer Assignments. Count areas as defined by Wauer during previous censuses conducted from 1967 through 2015, and 2022 volunteer assignments.
While the East Rim Trail was closed due to Peregrine Falcon nesting beyond backcountry campsite NE4, the National Park Service permit granted permission to survey this area, which included the area of the East Rim Trail from the intersection with the Boot Canyon Trail to the trail closure point near backcountry campsite NE4.
All singing birds were considered to be males on territory. Quiet birds within 400 feet (122m) of a singing bird were considered to be the female of the pair. With an area as rugged as the Chisos Mountains it is impossible to determine the exact number of birds present, but by using the same methods and monitoring the same areas on a regular basis, it is possible to collect valuable information regarding population trends over the years.
Results
The average number of Colima Warbler territories found in the original ten count areas is 54.2 pairs over the fourteen censuses performed to date. In 2022, 29 pairs were found in those same ten count areas, which is approximately 46% less than the average.
The average number of Colima Warbler territories found in all sixteen count areas is 58.5 pairs for all the censuses conducted to date. In 2022, 36 pairs were found in those same 16 count areas, which is approximately 38% less than the average. See the count area maps in the Appendices for warbler observation locations.
The count areas with the most Colima Warblers detected were Middle Boot Canyon (6b)/Upper Juniper Canyon (6c)/East Colima Trail (6a) and South Rim Trail (4b)/Upper Blue Creek/West Colima Trail (4a), each with 8 territories. Next highest was Lower Boot Canyon (7) with 4, followed by Emory Peak Trail(1b)/Upper Pinnacles Trail (1a) with 3. Upper Boot Canyon (5), Middle Pine Canyon (11), Middle Green Gulch (14), and Lower Green Gulch (15) each had 2, while East Rim Canyons (3), North Boot Canyon (8), Laguna Meadow Canyons (9), Lost Mine/Upper Pine Canyon (10), and Maple Canyon (16) each had 1. No warblers were found in Toll Mountain (2a), Campground Canyon (12), and Upper Green Gulch (13) count areas. Count areas that yielded higher than average numbers of warblers were South Rim Trail (4b)/Upper Blue Creek/West Colima Trail (4a) with 8 versus an average of 5.4, Lower Green Gulch (15) with 2 versus an average of 1.0, and Maple Canyon (16) with 1 versus an average of 0.3 territories. None of these above average count areas were affected by the April 2021 wildfire (see Discussion section).
In recent years, 2016, 2018, and 2021 were years of above average rainfall for the Chisos Mountains, at 22.77 inches (57.83 cm), 22.26 inches (56.54 cm), and 19.99 inches (50.77 cm) respectively, compared to an average of 18.44 inches (46.84 cm) from 1965 through 2021. However, 2011, 2013, 2014, 2015, 2017, 2019, and 2020 were all years of below average rainfall. 2020 holds the record for the second lowest total rainfall since the census has been conducted with 7.09 inches (18.01 cm), with the lowest total rainfall being 4.31 inches (10.95 cm) in 2011. Additionally, in 2022, the Basin had received only 0.53 inches (1.35 cm) of rain as of May 13th, against a typical mid-May average of 3.53 inches (8.97 cm). See Figure 3 for data comparing the average annual rainfall in the Chisos Basin with the results of the Colima census.
Figure 3. Chisos Basin Annual Rainfall & Colima Warbler Territories. Annual rainfall measured in the Chisos Basin of Big Bend National Park is provided online by the University of Utah’s MesoWest website.
Discussion
Colima Warblers were only sporadically singing on territory throughout both the first and second days of the survey period, as the overall conditions in the Chisos Mountains in May 2022 were substantially different from the previous seven years. The extensive wildfire in April 2021 that burned a total of 1,341 acres in the high country scarred a good portion of the landscape, including a majority of the prime Colima Warbler habitat (Figure 4). While the surviving oaks and maples had fully leafed out and grasses and other vegetation were on the rebound, the reduction in available habitat no doubt contributed to a lower observed population as well as a higher degree of dispersal.
Recent drought conditions also likely impacted the results, as no water was found in pools throughout the length of Boot Canyon during this census. Very little accumulated rainfall occurred in the Chisos Basin by the middle of May 2022, and these extremely dry conditions were preceded by multiple periods of prolonged drought. In addition, the survey was conducted under an unseasonable heat wave (91°F on the first day and 92°F on the second day, 10°F above average for May), presumably reducing the amount of time the warblers were vocalizing as they attempted to conserve their energy.
Other factors that have a probable effect on the numbers include (but are not limited to) the amount of suitable habitat in the warblers’ wintering range, the relative abundance of year-round food supplies, and the ability of the warblers to find suitable breeding habitat in other areas such as the nearby Maderas del Carmen mountain range. While the relative contribution of these factors falls outside the scope of this census, it is our hope that the ability of the warblers to redistribute themselves throughout the mountains as conditions change year to year, may help to restore the relative stability of their total population in the Chisos Mountains.
Figure 4. 2021 Wildfire Boundary and Colima Warbler Count Areas. The 1,341-acre area burned by the wildfire of April 2021 (in red) and the prime Colima Warbler habitat as represented by the count areas (in green). While boundaries are approximate, significant overlap exists. Note that Campground Canyon and Maple Canyon count areas are out of the scope of this map, but neither were affected by the wildfire. Wildfire map provided by the National Park Service.
References
Beason, Robert & Roland H. Wauer. 1998. Vermivora crissalis, Colima Warbler. The Birds of North America, No. 383. Cornell Laboratory of Ornithology & Academy of Natural Sciences.
Howell, Steve N. G., and Sophie Webb. 1995. A Guide to the Birds of Mexico and Northern Central America. New York: Oxford University Press.
Wauer, Roland H. 1996. Report on 1996 Colima Warbler Census and Assessment. Unpublished report to the National Park Service. 16 pp.
Wauer, Roland H. 2000. Report on 2000 Colima Warbler Census. Unpublished report to the National Park Service. 9 pp.
Wauer, Roland H. 1996. Field Guide to Birds of the Big Bend. Houston: Gulf Publishers.
Weber, James J & Lynne M, 2005. Report on the 2005 Colima Warbler Census. Unpublished report to the National Park Service. 23 pp.
Weber, James J & Lynne M, 2010. Report on the 2010 Colima Warbler Census. Unpublished report to the National Park Service. 26 pp.
Weber, James J & Lynne M, 2015. Report on the 2015 Colima Warbler Census. Unpublished report to the National Park Service. 24 pp.
Acknowledgements
We wish to thank all of the hardy volunteers (nearly all of whom are professional field biologists) for their willingness to backpack and hike on and off trail through the mountains and steep canyons during an unrelenting heat wave! Special thanks to Thomas Athens for handling the on-site logistics with the National Park Service. We’d also like to acknowledge Ashelynn, 9-year-old daughter of volunteers Jennifer Reidy and Randy Cartwright, who completed the entire 9+ mile hike up the Pinnacles Trail, over the Colima Trail, and down the Laguna Meadow Trail in search of Colima Warblers. Lastly, we owe a debt of gratitude to Ro Wauer for sharing his infectious enthusiasm for Big Bend National Park and for motivating us to once again undertake this sometimes challenging but always rewarding project.
Appendices
Count Area Datasheet Example
Count Area Maps with Colima Warbler Observation Locations
Number = Represents a confirmed observation made by the volunteers assigned to that count area.
Letter = Represents a confirmed observation made by the volunteers not assigned to that count area and not considered to be a duplicate observation. All efforts were made to avoid counting duplicates.
Numbers + Letters = Represents the total number of observations in a count area (as depicted in Table 2).
2022 Colima Warbler Census Volunteers
Athens, Thomas Big Bend National Park, TX
Balogh, Aaron Austin, TX
Berg, Sam Austin, TX
Black, Laura Austin, TX
Cartwright, Randy Liberty, MO
Chenoweth, John Austin, TX
Clark, Travis Austin, TX
Durish, Nevin Austin, TX
Fushille, Paul Dripping Springs, TX
Gosselin, Amber Austin, TX
Hoyt, Cathy Big Bend National Park, TX
Hull, Jeremy Austin, TX
Huryn, Eugene Tuscaloosa, AL
Kuhl, Audrey Austin, TX
Kuhl, Hannah Austin, TX
Kuhl, John Austin, TX
Kuhl, Sherri Austin, TX
Ledezma, Crystal Kerrville, TX
Luschen, Megan Austin, TX
Macedo, Danielle Austin, TX
McCann, Cait Austin, TX
Meisenhelder, Kelsey Austin, TX
Morgan, David Austin, TX
Moulton, Laurel Austin, TX
Negele, Christy Big Bend National Park, TX
O’Keefe, Kim Austin, TX
Ott, Silas Austin, TX
Owen, Jack San Antonio, TX
Owen, Victoria San Antonio, TX
Perez, Karen Austin, TX
Proppe, Darren Austin, TX
Reidy, Jennifer Liberty, MO
Reiner, Bill Austin, TX
Rudokas, Sara Austin, TX
Sandoval, Nancy Austin, TX
Scalise, Jonny Austin, TX
Scoggins, Link Austin, TX
Stewart, Audrey Austin, TX
Swanson, Romey Austin, TX
Vandenberg, Tom Big Bend National Park, TX
Weber, Jim Austin, TX
Weber, Lynne Austin, TX
Ode to Colima Warbler Watchers by Lynne Weber (2010, updated 2022)
We came from in and out of state
A sturdy, motley crew
To look for Big Bend’s specialty
As birders often do
Seven years had passed, the call went out
For those up to the quest
All just to see this crazy bird
Again we gave our best
The terrain was steep and rocky
Our packs were never light
As we searched the wooded canyons
For a Colima Warbler sight
We scanned the oaks and junipers
And tripped a time or two
Braved the thorns and cactus spines
Just to get a view
The weather was our fickle friend
Mother Nature always rules
Both days were scorching, searing heat
We wished for winds to cool
We left with scrapes and scratches
Sore muscles and some pains
But once again with memories
Of where rainbows wait for rain!
| Colima Warbler perched in a Drooping Juniper (Juniperus flaccida). Photo taken by Jim Weber on 5/5/2010 in Boot Canyon, Big Bend National Park. |
