On a nine-month trek covering nearly 1,000 miles, an Arizona photographer witnesses the wild biodiversity of the Madrean Sky Islands
I FIRST HEARD OF THE MADREAN SKY ISLANDS while taking a naturalist course in Tucson, Arizona, in 2023, and I was immediately intrigued. Stretching from southern Arizona and New Mexico into Mexico, this archipelago of roughly 63 independent mountain ranges contains an array of distinct biomes, as the elevation changes from desert floor to subalpine ecosystem. Here, weather from the temperate Rocky Mountains to the north and the subtropical Sierra Madre Occidental to the south collides, producing particular conditions, with each range a microcosm unto itself.
“The Sky Islands are a rich crossroads, where temperate and subtropical species intermix and find refuge among the forested mountains, foothill grasslands and valley deserts,” says , a program director with the conservation group .
This convergence of climates creates one of the most biodiverse areas in the world, according to the U.S. Geological Survey, with unique habitat in every range. More than 7,000 plant and animal species flourish here, including the planet’s northernmost jaguars and smallest owl, the . The Madrean Sky Islands also are home to endemic wildlife, such as the , a federally endangered species that lives only near the top of Mount Graham (10,720 feet) in southeast Arizona’s . The squirrels cannot survive in the extreme desert lowlands and are therefore stranded, so to speak, on their island.
As a conservation photographer, I try to understand as much as possible about the areas where I work. In the Madrean Sky Islands, each range has a specific ecosystem and distinct wildlife, including endangered and endemic species, making them vulnerable to threats such as climate change and human development. As I researched the ranges, I was fascinated to learn that more than half of North ʹappƽ̨’s bird species can be found here and that many of the islands have not yet been fully explored.
To sate my curiosity, I decided to plan a trek that would link multiple sky islands in Arizona via the Sonoran Desert valley floor. My thru-hike would take me nine full months, from February to October 2024; would cover elevation from 2,300 feet to just under 10,000 feet; and would traverse seven Madrean Sky Island ranges and nearly 1,000 miles. The slideshow below highlights some of what I saw.
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From a base elevation of 2,500 feet to a high point of Arizona’s Mount Lemmon soaring over 9,150 feet, the more than 200-square-mile Santa Catalina Mountains cover multiple different biomes that host unique wildlife. I began this portion of my route maneuvering around towering saguaro cacti in the Sonoran Desert.
As I hiked the Santa Catalinas, I passed western diamondback rattlesnakes, and by the time I finished, I was in a tree line of ponderosa pines, with squirrels chattering above me.
Due to its annual snowfall of about 15 feet, the Santa Catalina Mountains feature magnificent wildflowers in wet years. I had the pleasure of seeing mariposa lilies and Catalina beardtongue, and I spotted mammals such as the white-tailed deer and white-nosed coati. Generally considered subtropical and found as far south as Colombia, the coati thrives in a few of the Madrean Sky Islands.
I left part of my heart in the subdued but impressive Tortolita Mountains northwest of Tucson. At 25 million years old, they are among the geologically oldest of the Madrean Sky Island ranges and, due to age and weathering, they’re also among the lowest in elevation. Water is extremely limited; much of the harsh landscape offers virtually no shade; and if the monsoons come in summer, flash flooding is severe. If you imagine the Sonoran Desert, this saguaro-studded landscape is likely what comes to mind, and yet the full picture is much more complex.
Despite the arid environment of the Tortolita Mountains, oak woodland and riparian habitats take root above the valley floor, and deep canyons provide occasional reprieves from the heat. Out of all the sky islands I visited, I saw the most biodiversity here, including Gila monsters.
While traversing the Tortolita Mountains, I encountered javelina, bobcats, coyotes, green lynx spiders, snakes and lizards galore.
I also saw many bird species in the Tortolitas, including cactus wrens and Gambel’s quail.
The Madrean Sky Islands are also a hot spot for bees, hosting more species—including the native cactus chimney bee and the globemallow Andrena (on a globemallow bloom)—than anywhere else in the world. This range taught me not to judge biodiversity on first glance.
In the Santa Rita Mountains, southeast of Tucson, I witnessed the most incredible variety of birds, from the charismatic acorn woodpecker to the elegant trogon—a Central ʹappƽ̨n native that spends its summer breeding season in four Madrean Sky Island ranges.
Throughout my traverse, I cataloged the species I observed and journaled about wildlife encounters, challenging moments and my hopes for the miles to come.
Funnel web spiders were one of the many species I catalogued in my journal.
Near the end of my time in the Santa Ritas, on a hot afternoon in late June, I watched a blond black bear surrounded by beautiful pointleaf manzanita and native alligator juniper. This color morph helps the bear stay cool and blend in with low-elevation grasses.
From the summit of Arizona’s Mount Wrightson (9,456 feet) in the Mount Wrightson Wilderness (above), I spotted rare signs of human activity in the distance: copper pit mining—a reminder that, even in these remote habitats, the threat of development is always encroaching.
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