Whiskered Screech-Owl (Megascops trichopsis) in New Mexico

Background
The Whiskered Screech-Owl (Megascops trichopsis), an unassuming gnome of Madrean pine-oak forest, is among the most understudied owl species in North America. The ability for M. trichopsis to disperse into appropriate habitat is an important conservation issue, particularly in light of recent political pressure to create an artificial border demarcating the southern boundary of the United States with Mexico. This is even more pertinent when considering recent trends in an increasingly chaotic and unpredictable climate. A decrease in suitable habitat due to degradation from climate change and increasingly fragmented habitat due to human activities along international borders could put this poorly understood species at risk of extirpation from its range in the United States and more specifically, New Mexico.

For birders coming from most of the United States, M. trichopsis represents another species on the list of southeastern Arizona "specialty" birds. Denizens of the Central America and Mexico that, by fortune of geo-political boundaries, reach the northern limit of their range in the isolated sky-islands of Madrean pine-oak habitat amid a sea of parched desert landscape just north of the US/Mexico border.
Despite the relatively close proximity of this species to one of the Southwest's largest population centers (Tucson, AZ), M. trichopsis remains understudied within its range in the United States, in addition to being poorly known throughout the entirety of its range. Much of the published information on this species simply alludes to presumed similarities in biology with the more ubiquitous Western Screech-Owl (Megascops kennicotti).

Global distribution of Whiskered Screech-Owl (Megascops trichopsis)

(eBird)

The story of the occurrence of M. trichopsis in New Mexico is surprisingly well-documented, which isn't always the case for nocturnal species. Surveys of the Peloncillo Mountains, which are located in the extreme southwest corner (the "bootheel") of the state were included in a study conducted by Joe T. Marshall (Marshall 1957) from 1951-1955. Marshall did not detect any M. trichopsis in New Mexico (though he did find them in other ranges he surveyed in Arizona and Mexico). Later, J. David Ligon surveyed the Peloncillos in the 1970's. He did not find any from 1969 to 1973, but did detect M. trichopsis in 1974, which marked the first time the species had been documented in New Mexico (Ligon and Gene 1976).
Further surveying efforts were conducted by Sartor O. Williams III from 1990-2008. Over the course of these surveys Williams was able to document a general increase in the known New mexico population (Williams pers. comm.) The Peloncillos remain the only range within the state in which M. trichopsis are regularly encountered. There are a few records from the Animas Mountains, but it seems that this range is only sporadically occupied by M. trichopsis. There is a single unconfirmed report from the Big Burro Mountains in Grant County, NM which are approximately 140 km (86 miles) north and east of the Peloncillos.

Unlike its more northerly counterparts, M. trichopsis is thought to have a diet heavily reliant on moths and other nocturnal flying insects (Schulenberg 2010). When comparing the morphology of M. trichopsis to its fellow northern North American Screech-Owls (M. kennicotti and M. asio), several features become apparent. To start, the overall size of M. trichopsis is smaller than that of M. kennicotti and M. asio (Schulenberg 2010). M. trichopsis is largely a Central American species and the other two species have ranges largely at higher latitudes than M. trichopsis.By generalization, this seems to conform rather nicely to Bergmann's Rule. Though this rule generally applies more closely to populations of individuals within a single species distributed across a wide range of latitudes (those at higher latitudes showing larger body size than those at lower latitudes), it has also been applied to different species of the same clade.
Lending to the moth specialization theory is the fact that M. trichopsis have much more pronounced rictal bristles than either of its northerly contemporaries. These specialized, barb-like, contour feathers likely serve a sensory function, as well as preventing damage to the bird's eyes from the flailing appendages of an insect (Lederer 1972). Also, when comparing talon and foot sizes, M. trichopsis have daintier feet than M. asio or M. kennicotti. This would suggest that they rely less upon their ability to capture prey with said talons. A reliance on nocturnal insects as prey might serve as a limiting factor of distribution for this mostly (as far as is known) sedentary species.
Though speculative, it makes sense that the distribution of M. trichopsis is limited by the availability of year-round nocturnal insects (if they are in-fact moth obligates). M. asio and M. kennicotti in most of the US must rely on small mammals in the winter months as most areas *usually* are too cold to support insects in mid-winter. Hence bulkier talons and reduced rictal bristles compared to the petite and more specialized M. trichopsis.

Methods
Due to the paucity of published work regarding the species, it is difficult to recreate study methods used to survey for this species. During the previous efforts to survey for the species, the following canyons were investigated within the Peloncillo range.
Clanton Canyon- 8 pairs
South Clanton (Blackwater Draw)- 1 pair
Skeleton Canyon- 9 pairs
Whitmire Canyon- 3 pairs
Cottonwood Canyon- 2 pairs
A total of 23 pairs were reportedly discovered by Williams of the course of his work surveying for this species (Williams pers. comms.) The aim of a future study should be to survey the same canyons in an attempt to replicate coverage. This would allow the project to determine whether or not there has been a change in the population over the near decade of intervening time from Williams last year of surveying. Seeing as Williams described an increase in the population from the time of his survey efforts (Williams pers. comm.) in addition to the anecdotal evidence of perceived abundance from birders who were in Clanton canyon in September of 2016, it seems likely that the population had increased well beyond 23 pairs. The goal of a future study may also be to incorporate some additional canyons with appropriate habitat in order to provide a more extensive coverage of the potential range for M. trichopsis within the Peloncillos. To provide an extensive survey of the range, the following canyons should be considered for a survey network:
Clanton Canyon
South Clanton (Blackwater Draw)
Skeleton Canyon
Whitmire Canyon
Cottonwood Canyon (including Miller Spring, Stateline Tank, and Gravel Pit Tank tributaries)
Salt Canyon
Guadalupe Canyon (both upper and lower portions)
Most of this land falls under the jurisdiction of the Coronado National Forest, but lower Guadalupe Canyon is in fact on private land and special permission would need to be obtained in order to survey here.

Current known distribution of M. trichopsis in NM Most reports from the central Peloncillos which are also the most covered by birders

(eBird)

 To survey for this species, a point-count system will be implemented, similar in execution of the USGS Breeding Bird Survey. Surveys will mostly be completed on foot (no road access to most canyons), though Clanton Canyon will be competed via automobile as it does have road access (via Geronimo Trail). Survey points will be 300 meters apart from one another and all species detected will be noted for each point. The use of tape will be used to help elicit a response the following methodology will be used to help ensure consistency:

• An initial 30 seconds after arriving at the point to allow birds to adjust to presence of surveyor
• 1 minute spent listening for spontaneous vocalization
• 30 seconds of taped M. trichopsis song administered
• 1 minute of listening
• 30 seconds tape
• 1 minute listening

This technique will hopefully maximize the chances of a response while also having as little impact on the birds as possible.
It is worth noting that despite survey efforts and birder coverage, M. trichopsis has yet to be recorded in the lower portion of Guadalupe Canyon. There appears to be appropriate structure for nesting (i.e. cavities in trees of appropriate diameter), but no M. trichopsis. This question raises several potential answers. Perhaps competition with Elf Owl (Micrathene whitneyi) and M. kennicotti has led to the competitive exclusion of M. trichopsis from this area. There may also be an elevational component to the distribution of M. trichopsis, with lower Guadalupe Canyon being too low. This elevational preference may be a product of competition with M. whitneyi and M. kennicotti.

Lower Guadalupe Canyon: 1280-1360m (No M. trichopsis reported in NM despite efforts)
Middle/Upper Guadalupe Canyon: 1390-1680m (reported M. trichopsis)
Skeleton Canyon: 1430-1500m (reported M. trichopsis)

This pattern of distribution would suggest that M. trichopsis shows a preference for habitat above 1400m. The elevation of survey points will be an important consideration when interpreting the presence/absence data.

Data
See Page: Whiskered Screech-Owl (Peloncillo data) for data from surveys conducted by Egelhoff:

Whiskered Screech-Owl data (Egelhoff 2017)

Discussion
39 points were officially conducted along Geronimo Trail, which served as the line transect. With these points, and including the spontaneous encounter, 20 M. trichopsis were detected. 18 in New Mexico and 2 in Arizona.
Looking forward, it would obviously be pertinent to extend the surveys to the other canyons in the Peloncillo range, as well as re-conduct the current survey in March 2018 to ascertain a possible change in the current population. It may also be pertinent to determine the occurrence of this species in areas adjacent to the Peloncillos south of the border, as well as in adjacent Arizona in order to get a better representative sample of the population size. A comparison between the habitat requirements of this species in the United States versus more southerly latitudes may also yield interesting life history information.

Literature Cited

Gamel, CM; Bush, T, 2001. Habitat use, population density, and home range of Elf Owls (Micrathene whitneyi) at Santa Ana National Wildlife Refuge, Texas. Journal of Raptor Research 35: 214-220

Hardy, PC; Morrison, ML; Barry, RX, 1999. Abundance and habitat associations of elf owls and western screech-owls in the sonoran desert. Southwest Naturalist 44: 311-323

Lederer, R, 1972. The Role of Avian Rictal Bristles. Wilson Bulletin 84: 193-197

Ligon, JD; Gene, BL, 1976. First Record of the Whiskered Owl in New Mexico. Condor 78: 112

Marshal, JT, 1957. Birds of Pine-Oak Woodland in Southern Arizona and Adjacent Mexico. Pacific Coast Avifauna 32: 1-125

Schulenberg T.S, 2010. Whiskered Screech-Owl (Megascops trichopsis), Neotropical Birds Online. Ithaca: Cornell Lab of Ornithology; retrieved from Neotropical Birds Online:
https://neotropical.birds.cornell.edu/portal/species/overview?p_p_spp=206616
Accessed Oct. 10, 2016