Scientists are smart.
Given a choice between a cool mountain and a lab in the overheated desert, they'll make the right decision.
Courtney Conway arrived at the University of Arizona in the heat of August 2000.
"I said 'OK, I gotta find a way to get out of Dodge in the summer, and I don't want to drive any farther than I have to.'"
The wildlife researcher then spent a couple of days a week for the following 11 summers in Marshall Gulch, near the top of the Santa Catalina Mountains, keeping track of a population of red-faced warblers.
Conway, now at the University of Idaho, continues to supervise the work of UA graduate students who, like him, have found the forests atop our nearby "sky island" a cool place to watch birds.
Proximity to a major research university has made the Santa Catalinas one of the most studied sky island mountain ranges.
Proximity to a population of 1 million people has provided the scientists increasingly complex puzzles to solve.
There is a paved road to the summit, an array of radar and communications towers on the Catalinas' major peaks, a village of second homes, a ski area, campgrounds, picnic areas, sledding hills and popular hiking trails.
It is not a pristine laboratory.
Bird researcher Carl Lundblad stalks yellow-eyed juncos atop Mount Lemmon in a landscape that is more surreal than natural.
The defining features here are the giant communication towers owned by CenturyLink, Verizon and a variety of federal, state and local governments.
They dwarf the charred, 40-foot trunks of Douglas fir that burned in the Aspen Fire nine years ago and the topmost pylon of the chairlift at Ski Valley, the southernmost ski area in the United States.
A half dozen juncos, accustomed to the whine of generators that cycle on and off, and oblivious to the crunching tires of Lundblad's government-issue Ford hybrid utility vehicle, continue feeding in the forb-covered fringe of a dirt parking lot as we arrive on a recent Friday.
Lundblad begins observing through binoculars without leaving the vehicle. The juncos, members of the sparrow family, continue to feed as we exit quietly.
Then they fly off simultaneously as a Cooper's hawk casts a gliding shadow in the gold of early morning.
The yellow-eyed junco is a gray bird with a rust-colored patch on its back and bright yellow eyes. The species lives mainly in Mexico, but its range extends into the mountains of Southern Arizona and New Mexico. These particular birds spend their lives in the Catalinas, migrating vertically to mid-mountain in winter from their breeding grounds in the cooler, upper canyons.
In spring, Lundblad searches the forest floor for well-hidden nests and bands fledglings for later identification. He also bands adults after catching them in mist nets. He's looking now for some of the 900 birds he's banded over the years.
He's puzzled by one aspect of their behavior. Some juncos don't migrate down the mountain in winter. They gut out the cold weather and even some of the snowstorms.
There must be some evolutionary advantage for such brave behavior - and he'd like to find out what it is before he moves on to continue his graduate studies.
Vertical migration isn't something you can study just anywhere.
Shari Ketcham sets traps in more pristine locations. Her 200 sites, chosen at random by computer, are often far from roads and trails. The Catalinas have nearly 57,000 acres of designated wilderness and plenty of additional wild land.
Ketcham doesn't recompute coordinates unless they lead her to inaccessible cliffs.
She and her husband, Chad, have already hiked to the toughest sites, installing cameras and hair traps and returning a week later to collect them.
On this fall Saturday morning, she is only a mile from the paved highway, sliding down slopes and climbing over downed trees in a half-burned patch of ponderosa pine forest off the Box Camp Trail.
Ketcham and two assistants, Max Mazzella and Crista Schmidt, are collecting squirrel hair from double-sided tape in tube traps baited with peanut butter. She is also downloading photos from cameras attached to nearby trees.
The cameras have captured a variety of wildlife, from rodents to bears. They have also recorded multiple close-ups of inquisitive hikers.
The camera seldom captures her prey: the Arizona gray squirrel, a shy critter with round ears and a white-fringed tail as big as its 10-inch body.
The grays have always been rare in the Catalinas, but recently they've been "declining in abundance," said Ketcham, who is pursuing her master's degree in natural resources and environment while holding down a day job as special use assistant with the Santa Catalina District of the Coronado National Forest.
"We're trying to find out where they are, what kind of habitat they use, in case we need to come up with a conservation plan."
The gray squirrel's habitat has constricted with fire, and biologists believe it is being displaced by Abert's squirrels - tassel-eared cuties imported from around Flagstaff in the 1940s to increase hunting variety in the sky islands of Southern Arizona.
The gray squirrels, which once occupied the forest around Summerhaven, haven't been seen there in years, Ketcham said.
Abert's squirrels have "naturally colonized" the adjoining Rincon Mountains as well, said mammalogist John Koprowski, who supervises Ketcham's research and is director of the Mount Graham Red Squirrel Project in the Pinaleño Mountains.
The red squirrel, often called the most endangered mammal in North America, faces competition from Abert's squirrels in addition to the loss of its spruce habitat to moths, aphids, beetles and fire.
The Arizona Game and Fish Department brought the Abert's squirrels to a number of ranges in the 1940s "without a lot of forethought," said Koprowski.
They were thought to be "ponderosa pine obligates," he said, but they quickly spread into the mixed conifer forests in the upper reaches of the Catalinas and Pinaleños, where they competed with the natives for nesting spots and food.
Geoscientist Steve DeLong is taking laser-radar photos of a forest below Mount Bigelow that is considerably thinner than the last time he was here.
The U.S. Forest Service sent in logging crews to winnow this patch of Douglas fir, ponderosa pine and white pine. Trunks and limbs are heaped into slash piles that will be set ablaze when fire spread is less likely.
The thinning should improve the health of this section of over-crowded forest, protect it from catastrophic fire and provide the Northern goshawk with more open areas for hunting.
DeLong uses a laser-scanner that, once it is moved around to unveil the trees hiding behind other trees, will produce a "point cloud" of every stem and all the foliage in this stretch of forest.
LiDAR (light detection and ranging) is a relatively new tool for forest researchers, though it has been used for years by geographers and hydrologists for surface mapping.
DeLong's measurements are crucial to Rebecca Minor and Greg Barron-Gafford, researchers with the UA's Biosphere 2, who have been taking measurements of the moisture and carbon dioxide captured and released by the plants on this ridge beneath Mount Bigelow.
Their main atmospheric measurements are taken at the top of a nearly-100-foot tower, where two claw-shaped sonic anemometers give a 3-D picture of wind currents and an infrared laser device captures moisture and carbon-dioxide content 10 times each second.
That information is combined with temperature, humidity, soil-moisture, rainfall, snowpack and sap-flow readings to take the pulse of the forest - the capture and release of carbon dioxide and the use of water.
DeLong's before-and-after LiDAR point clouds will allow the researchers to account for the missing biomass.
Barron-Gafford and his partners in the U.S. Department of Agriculture collect data from similar flux towers across Southern Arizona. This one has been operating since 2003.
A longer record of precipitation at the Bigelow site will be teased from tree-ring data taken by UA dendrochronologist Valerie Trouet and her graduate students.
The tree-ring researcher and her team marked 50 trees to proportionally represent the mix of ponderosa, white pine and Douglas fir in this swath of forest and have started coring them to extract samples.
They are using a 10-millimeter increment borer to extract a sample core, and the going is tough.
Students take turns on the final twists of the borer handle.
A 5-centimeter borer is big enough to determine the age of trees, but these cores will be analyzed for isotopic ratios of oxygen and carbon and bigger samples are required, said graduate student Ross Alexander.
Isotopic analysis yields more information about the climate that grew these trees and how it has changed over time.
The tree-ring record for the Catalinas is extensive. Edmund Schulman compiled the first chronology for Douglas fir on Mount Lemmon in 1940, just three years after A.E. Douglass established a tree-ring lab at the UA.
Schulman's chronology went back to 1545. That was pushed back in 1998, when UA researchers found a Douglas fir in the Reef of Rocks area that germinated in 1320.
The ancient forest atop the Catalinas, like many Southwestern forests, is hurting from the impact of 15 years of intermittent drought and threatened by expected rising temperatures in the coming decades.
The "net ecosystem exchange" at the UA's Bigelow site already shows a definite trend. "CO2 levels are increasing year by year," said Barron-Gafford, the Biosphere 2 researcher.
Healthy forests aid the fight against global warming by trapping and storing carbon. Unhealthy forests aren't effective carbon sinks, and they tend to burn easily, releasing their carbon all at once.
Fire has already blazed through this range with dramatic effect. In 2002 and 2003, the Bullock and Aspen fires devastated big swaths of it. The Aspen Fire destroyed most of the homes in Summerhaven in a crown fire that killed off entire stands of trees.
Less fierce, but equally extensive, fires once burned across the top of this mountain every 10 to 15 years, said fire ecologist Tom Swetnam, director of the UA Laboratory for Tree-Ring Research, but they were stamped out repeatedly between 1910 and the beginning of this century.
The Forest Service has underwritten studies on how to restore fire as a management tool in the Catalinas, and recovery from fire has become an active field of study.
"There has been a resurgence of research since the Aspen and Bullock fires," said Forest Service spokeswoman Heidi Schewel.
Researchers also want to know how recent fires affected the flora and fauna on the mountain.
For Ketcham's research on the gray squirrel, she selected an equal number of sites that burned at low, medium or high intensity. Early data indicate the gray squirrels prefer undamaged forest.
The gray squirrels are not alone in their precarious perch atop this mountain.
Jim Peña, associate deputy chief of the National Forest system, told Congress last year that the sky islands of the Coronado National Forest host 25 threatened or endangered species - more than any other national forest. An additional 162 are listed as "sensitive," Peña said.
These mountains are also being invaded by unwelcome species, including the notorious grasses imported to Arizona for cattle feed or erosion control - buffelgrass, cheatgrass, red brome and Lehmann's lovegrass.
Things were simpler, but a good deal tougher, when scientists first explored the Catalinas.
On a honeymoon trip in 1881, botanists John and Sara Lemmon tried and failed to reach the summit from the south side.
They finally found their way on horseback via E.O. Stratton's Pandora Ranch on the north side, according to Suzanne Hensel's history, "Look to the Mountains."
Stratton was so impressed by Sara Lemmon's stamina that he christened the range's 9,157-foot peak "Mount Lemmon" in her honor.
The Lemmons found a number of unknown species on their trip, emblematic of the scientific riches that awaited discovery.
Did you know?
Edmund Schulman, who compiled the first tree-ring chronology of Douglas fir on Mount Lemmon in the 1930s, was the first to research what turned out to be the oldest trees on Earth: the bristlecone pines of the White Mountains of California.
There, he discovered "Methuselah," germinated in 2832 B.C. - still the oldest living tree ever found.
• Oct. 28: How the mountains formed - and how they create what lies beneath them.
• Today: Tucson's sky island: birds that migrate vertically; native vs. non-native species; fire on the mountain.
• Nov. 11: Looking at stars and guarding against meteorites - new uses for aging telescopes and top-secret facilities.
Contact reporter Tom Beal at firstname.lastname@example.org or 573-4158.