Sonoran Desert Natural Events Calendar
Spring
Late February, March, April
March
Average high: 71.9°F (22.2°C)
Average low: 43.8°F (6.6°C)
Relative humidity at 5 am: 53%
Relative humidity at 5 pm: 23%
Normal rainfall: .71” (18.0mm)
Spring begins in earnest in the desert, with warm and sunny days and cool nights; days are warming in the high country—enough to begin melting snow and filling creeks; we hear that magical sound of running water.
Flora
March is wildflower month. Look for dozens of wildflower species, including globe mallows, penstemons, evening primroses, desert marigolds, blue dicks, gilias, bladderpods, dock, chia, desert hyacinths, and many more. Many shrubs bloom as well, including desert lavender, hop bush, brittlebush, and Mormon tea.
Fauna
Many animals are breeding or preparing to breed. Elf owls arrive from wintering grounds in Mexico to breed in saguaro-mesquite desert; males arrive first and try to win females with their distinctive barking call as they perch in cavities in saguaro cacti or other trees. Burrowing owls and barn owls, which are also found in desert or even urban areas, also breed this month. Migratory songbirds begin to arrive, either to breed or to rest on their way to northern breeding grounds; riparian areas are especially good places to see them. Desert tortoises and desert box turtles emerge from burrows and begin to mate. Turkey vultures move back to southern Arizona for the summer.
Nature Watching Tips for March
Spring bird migration is an exciting time to head out to riparian corridors,
where many songbirds rest en route to northern breeding grounds or stop
to breed here in southern Arizona. Good bets include the Anza Trail along
the Santa Cruz River near Tubac, Sabino Canyon in northeast Tucson, Ciénega
Creek east of Tucson, Hassayampa River Preserve northwest of Phoenix,
Boyce Thompson Southwestern Arboretum east of Apache Junction, and the
San Pedro National Riparian Conservation Area near Sierra Vista. The intersection
of Baseline and Salome roads, approximately fifty miles (80 km) west of
Phoenix, is a wonderful place to look for Bendire’s, sage, crissal and
Le Conte’s thrashers through the end of March. Also, contact the Tucson
Audubon Society at (520) 629-0510 and the Audubon Society of Maracopa
County at (602) 631-9761 about their birding tours. 
April
Average high: 80.5°F (26.9°C)
Average low: 50.1°F (10.1°C)
Relative humidity at 5 am: 42%
Relative humidity at 5 pm: 16%
Normal rainfall: .31” (7.9mm)
Dryness begins to settle on the desert, with just a few days of possible sprinkles. Spring weather arrives in the mountains, with days in the 60s (>15°C) and only half the nights dropping below freezing.
Flora
The desert “bean” trees (legumes such as blue palo verdes, catclaw acacias, and mesquites) begin to open yellow to creamy blooms, and the cacti begin to bloom as well, with a few of the prickly pears, chollas, and hedgehogs starting off. By the end of the month, some saguaro cacti will open their big, white flowers. Brittlebush may still bloom; look for iron-cross blister beetles—they are black, yellow and red with black cross patterns on their backs—feeding on the brittlebush blossoms.
Fauna
Bird migration continues. Summer’s hawks, including Swainson’s, zone-tailed and Black hawks, begin to arrive and get busy finding mates for the summer breeding season. In mountain canyons around Tucson many hummingbirds arrive and breed, including broad-billed, black-chinned and magnificent. White-winged doves also return and fill the late-spring air with the signature summer call, “Who-cooks-for-you?”As the days lengthen and warm up, reptiles become more visible—time to watch for rattlesnakes (although remember they can be out any month of the year). Desert iguanas, lesser earless lizards and western whiptail lizards begin breeding. Bobcats, coyotes and foxes are having litters. And butterfly activity picks up; look for great blue hairstreak, hackberry, skipper, blue, and queen butterflies.
Nature Watching Tips for April
A walk up Romero Canyon Trail in Catalina State Park may yield some late-spring
wildflowers and good butterfly activity in late morning and throughout
warm afternoons. Before the trail climbs the western slopes of the Santa
Catalina Mountains, it crosses through a mature mesquite bosque (Spanish
for forest) where you can look for songbirds, hummingbirds, and white-winged
doves. For information on the park, call (520) 628-5798. April is also
a good time for people in the Phoenix area to look for warblers, flycatchers
and Bullock’s orioles in the Forest Service picnic areas on Bush Highway
along the Salt River.