Wildlife Cameras at Organ Pipe Cactus National Monument, 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 at Organ Pipe Cactus National Monument 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. Knowing how species respond takes data from many species at once, over wide areas.

A wildlife camera at Saguaro National Park, Tucson Mountain District.

Remote cameras collect that without disturbing the animals. Animals with unique markings, such as jaguars, can be told apart one by one, and their numbers estimated by mark-recapture methods. Most cannot be, so SODN uses occupancy modelling instead:

• 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. Occupancy models account for those misses statistically, in a framework that has existed since 2002.
• Covariates help explain why. Some, such as elevation, stay fixed during sampling and probably affect whether a species occupies a site. Others, such as temperature or rain, change daily and may affect whether it is detected: animals can be harder to see and less active in great heat.
• Over several years, occupancy, which is often used as a stand-in for abundance, shows whether a species is increasing, stable or decreasing. Following the effect of temperature and rain helps managers judge what climate change may do.

How the cameras worked in 2021

• In March 2021 field crews set up 61 cameras at unbaited, permanent monitoring sites across the monument, chosen mostly by a spatially balanced random design. They went in the same places and with the same settings as in earlier years, on stakes or strapped to trees and other structures.
• Triggered by motion or a sudden change in temperature, the cameras took photographs from March 11 to April 25, and were then collected.
• In the office, technicians removed the "false triggers" (photographs with no animal), sorted the rest, the "detections", with Colorado Parks and Wildlife's Photo Warehouse database, and exported the metadata for analysis.
• Volunteers usually help set up and collect the cameras. Because of COVID-19 safety concerns, none took part in 2021.

Field crews deployed 61 wildlife cameras at Organ Pipe Cactus National Monument in 2021.

The cameras have gone out at the same places and the same time of year every year since 2016, except in 2019, because of the federal government shutdown. That makes five years of data. The number of photographs containing an animal has ranged from 575 to 3,738 a year.

What the cameras saw

The cameras made 809 detections: 478 of mammals identified to 16 species, 272 identified only to genus or family, 49 of mammals that could not be identified, and 10 of birds (three species and an unidentified bird).

Wildlife detections from 61 cameras at Organ Pipe Cactus National Monument, March 11 to April 25, 2021.

At 24 camera sites, at least one species turned up that had never been recorded there before, which the network reads as a rise in wildlife activity at those sites. The notable new records were American badger, antelope jackrabbit, bighorn sheep, Sonoran pronghorn, western spotted skunk and white-tailed deer. All are uncommon or even rare at the monument, so finding them active at new locations is an encouraging sign.

An example: black-tailed jackrabbits 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, which ruled out chipmunks, rats and mice, and that were detected at more than 30% of sites, which ruled out rarer species such as the Sonoran pronghorn. Covariates were kept only if they had some explanatory power (p < 0.10).

Occupancy probability of black-tailed jackrabbits against slope at Organ Pipe Cactus National Monument: the average in green, the standard error in grey.

For black-tailed jackrabbits, slope mattered. On the monument's flatter ground their occupancy probability is high, 60–87%; on slopes steeper than 12 degrees it drops below 25%. The model suggests the jackrabbits 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 the species uses the monument, and how much a single season's data can tell.

Sources

• National Park Service, Sonoran Desert Network, "Wildlife Monitoring at Organ Pipe Cactus National Monument, 2021," prepared by Elise Dillingham and Alex Buckisch. https://www.nps.gov/articles/000/sodn_wildlife-monitoring-organ-pipe-2021.htm (PDF)
• D. I. MacKenzie and others, "Estimating site occupancy rates when detection probabilities are less than one," Ecology 83 (2002): 2248–2255.
• Corrected: the white-tailed deer's genus, given as "Ococoileus" in the original table, to Odocoileus.