Wildlife Cameras at Saguaro National Park's Tucson Mountain District, 2021

The National Park Service's Sonoran Desert Network (SODN) uses remote wildlife cameras to monitor medium- and large-sized mammals in park units across the Sonoran Desert and Apache Highlands. The monitoring began in 2016. Its goal is to detect biologically significant changes in mammal populations and communities over time, and to give park managers reliable information on their status and trends. This page summarises what the cameras found in the Tucson Mountain District (TMD) of Saguaro National Park in 2021.

Why cameras, and what occupancy means

Pressures such as habitat loss and climate change are pushing species to shift where they live, and they need large tracts of suitable habitat to do it. National parks provide some, though they are not immune to disturbance themselves.

A wildlife camera in Saguaro National Park's Tucson Mountain District.

Remote cameras record many species at once, over wide areas, without disturbing them. Animals with unique markings, such as jaguars, can be told apart one by one; most cannot, so SODN uses occupancy modelling:

• Occupancy is the share of an area a species inhabits. A species photographed at a site is present; one not photographed may be absent, or present but missed, and the models account for those misses statistically.
• Covariates help explain why. Fixed ones, such as elevation, probably affect whether a species occupies a site; changing ones, such as temperature or rain, may affect whether it is detected.
• Over several years, occupancy, often used as a stand-in for abundance, shows whether a species is increasing, stable or decreasing.

How the cameras worked in 2021

• In January 2021 field crews set up 60 cameras at unbaited, permanent monitoring sites across the district, chosen by a grid-based, spatially balanced design, in the same places and with the same settings as in earlier years.
• Triggered by motion or a sudden change in temperature, they took photographs from January 5 to February 25, and were then collected.
• Only 57 returned data: one was stolen and never recovered, and two malfunctioned.
• Technicians removed the "false triggers" (photographs with no animal), sorted the "detections" with Colorado Parks and Wildlife's Photo Warehouse database, and exported the metadata for analysis.
• Volunteers usually help with the fieldwork. Because of COVID-19 safety concerns, none took part in 2021.

A field crew member celebrates an extraordinarily tall saguaro on the hike to a monitoring site.

Cameras have gone out at the same places and time of year every year since 2017, except in 2019, because of the federal government shutdown: four years of data. The number of photographs containing an animal has ranged from 1,994 to 4,054 a year.

What the cameras saw

The cameras made 1,567 detections: 1,373 of mammals identified to 13 species, 33 identified only to genus or order, 28 of mammals that could not be identified, and 133 of birds (six species and some unidentified birds).

Wildlife detections from 57 cameras in Saguaro National Park's Tucson Mountain District, January 5 to February 25, 2021.

At 25 camera sites, at least one species turned up that had never been recorded there in earlier years, which the network reads as a rise in wildlife activity at those sites. The notable new records were American badger, ringtail and mountain lion, all uncommon or even rare in the district. No camera had caught a mountain lion since 2018; in 2021 there were seven detections.

An example: coyotes and slope

Trend models need several consecutive years of data, but a single season can still answer narrower questions. The network fitted a single-season, single-species occupancy model with the R package "unmarked", grouping detections into seven-day periods. It chose nine species that the cameras can reliably identify, at least 43 centimetres long, the size of a rock squirrel, and that were detected at more than 30% of sites, which ruled out rarer species such as the American badger. Covariates were kept only if they had some explanatory power (p < 0.10).

Occupancy probability of coyotes against slope in Saguaro National Park's Tucson Mountain District: the average in green, the standard error in grey.

For coyotes, slope mattered. On the district's flatter ground their occupancy probability is high, 60–80%; on slopes steeper than 11 degrees it drops below 20%. The model suggests coyotes prefer flat ground, likely because it gives easier access to food, water and cover than the barren, rugged, hard-to-cross steep areas. The result shows managers how coyotes use the park, and how much a single season's data can tell.

Sources

• National Park Service, Sonoran Desert Network, "Wildlife Monitoring at Saguaro National Park's Tucson Mountain District, 2021." https://www.nps.gov/articles/000/sodn_wildlife-monitoring-saguaro-tmd-2021.htm
• Corrected: the black-throated sparrow's genus, given as "Amphispizia" in the original table, to Amphispiza.