What to look for in nature in Colorado this May

What is happening along Colorado's creeks, rivers and ponds in May?

• Medano Creek and its surge waves

  Flow builds through May; late May and early June are the best odds for surge waves · Great Sand Dunes National Park and Preserve, San Luis Valley

  Medano Creek runs along the base of the great dunes, and in a good year it does something rare: it moves in waves. The National Park Service calls this surge flow, water pulsing across the sand in swells. The creek usually reaches the main dunes parking area in April as a trickle, then deepens through May. In an average year the park puts the peak at roughly 40 cubic feet per second, a reading taken about five miles upstream of the main parking area, so it shows the trend rather than what you will find at the dunes. In average or wetter years the waves can be high enough for children to float short stretches on flat inflatable toys.

  Snowpack decides everything. The park notes that not every year brings enough water for floating or for surge waves, and that by late June the creek is usually an inch or two deep or drying up. Late May and early June weekends are very crowded, and the park suggests going on a weekday. Memorial Day weekend in 2027 is May 29 to 31. Mosquitoes become numerous around the second week of June, so May is the more comfortable month. The park posts live creek flow and a conditions page; look at it before the drive, and leave plants and animals alone.

• The Mother's Day caddis hatch on the Arkansas River

  Usually late April into May; set by water temperature, not the calendar · The Arkansas River, with Salida a center of the local festival

  Anglers call the first big insect hatch of the Arkansas River season the Mother's Day caddis hatch, although it often starts weeks before Mother's Day, which is May 9 in 2027. A fly-fishing retailer's guide says the hatch typically starts in late April and peaks in early May, set off when the water reaches about 54 °F, and warns that extra snowmelt can chill the river and delay it. That is a commercial source, so treat the timing as a rule of thumb. Trout Unlimited's Collegiate Peaks Chapter has held a Caddis Festival banquet and auction in Poncha Springs; we found no 2027 date, so check with the chapter.

  You do not have to fish to enjoy it. A good caddis evening shows up as insects bouncing over the surface and trout rising to meet them. If the river is high and brown with runoff, the hatch can be washed out for the year.

• Boreal toads at high ponds

  Breeding runs from about mid-May to early July, depending on snowpack · Ponds and wet meadows from about 8,000 to 11,500 feet, including Rocky Mountain National Park

  The boreal toad is the only toad of Rocky Mountain National Park, according to the park service, and it is in trouble. The park says the population has declined steeply over thirty years, that breeding was documented at twenty historic sites but in the past fifteen years at only six areas, and that a fungal disease called chytrid is thought to be a major cause. The toad has been on Colorado's endangered species list since November 1993. In spring the toads leave their winter hiding places and gather at communal breeding ponds; a female can lay up to 16,500 eggs, and in cold high ponds development can take about 75 days.

  You are unlikely to meet one by accident, and because the species is in decline you should keep to trails near any pond and never handle a toad. Simply knowing that the gathering is under way, high above the towns while the snow melts, is part of what May means in the mountains.

• Plains spadefoots after a storm

  After heavy rain in spring or summer · Eastern plains and the San Luis Valley, in rain-filled pools and stock ponds

  A plains spadefoot spends most of its life buried in the soil and comes out to breed only after heavy rain fills a temporary pool. Colorado Parks and Wildlife describes the call as a brief snore, much faster than the stuttering snore of the New Mexico spadefoot, and says tadpoles usually change into small toads within three to ten weeks, which is fast enough to beat a drying pond. The species is described as common on the eastern plains and in the San Luis Valley. If a thunderstorm soaks a pasture on a warm May night, a flooded roadside ditch or stock pond may be loud by dark. Drive carefully on wet roads; the toads are small and easy to miss.

• Runoff and the cold river

  Rising through May and June in most mountain valleys, with timing set by the winter's snowpack · Mountain rivers and creeks statewide

  Mountain rivers and creeks rise as the snowpack melts, and the size and timing of the crest depend on how much snow fell that winter. Colorado Parks and Wildlife says the water here stays cold until at least midsummer, which is why a river that looks inviting on a warm afternoon can be dangerous. Cold-water details are in the safety notes below.

Where can I see lark buntings and prairie wildlife in Colorado in May?

• Lark buntings

  Flocks arrive in spring; males are displaying and pairs are settling in May · Plains and prairie, especially the Pawnee National Grassland in Weld County

  A breeding male lark bunting is black with a bold white wing patch, and it is Colorado's state bird. A Summit Daily nature column describes the display: the male flies almost straight up on rapid wingbeats, hangs for a moment near the top of a climb of about 10 to 30 feet, then drifts down on jerky, butterfly-like wingbeats while singing. The courtship period lasts about two weeks, after which the flocks spread out to nest sites. The nest is a cup on the ground, usually under a low branch or in a shrub, with two to six pale blue eggs that hatch after about 12 days. The same column notes that numbers swing from year to year.

  Look for them on fence wires, yucca stalks and low shrubs, and listen for the song carrying across open ground. Stay in the vehicle or on the road.

• A morning on the Pawnee National Grassland

  Open all year in daylight; May is a good month to go · Pawnee National Grassland, western section, northeast of Greeley

  The Colorado Birding Trail lists the western section of the Pawnee as a stronghold for prairie specialists: ferruginous hawk, mountain plover, long-billed curlew, burrowing owl, McCown's and chestnut-collared longspurs, grasshopper sparrow and lark bunting, with pronghorn, black-tailed prairie dogs and, occasionally, a swift fox. The listing does not say when each species is present, so treat the list as a menu rather than a schedule. It does say you can watch from the car, parking is by the roadside, and there are no restrooms, water, trails or camping on site. Crow Valley Campground is the nearest camping, and lodging is in Greeley.

  The same page warns that the grassland is a remote patchwork of federal, private and leased land, so a good map is essential, and to beware of rattlesnakes and bring water. Respect fences and signs.

• Spring babies at Rocky Mountain Arsenal

  Spring into early summer · Rocky Mountain Arsenal National Wildlife Refuge, near Denver

  The refuge's seasonal guide lists what to look for in spring: cinnamon-colored bison calves beside their mothers, prairie dog pups and black-footed ferret kits venturing out of burrows, fawns appearing from the locust thickets, and the loud begging calls of black-billed magpie chicks from their enormous stick nests. Bullock's orioles, warblers, finches and other migrating songbirds pass through the woodlands. Burrowing owls are listed under summer, when they nest in unused prairie dog burrows. Visit in the early morning or late afternoon, keep to the trail, and let the young animals come and go on their own terms.

Which birds pass through Colorado in May, and where can I join in?

• Spring bird banding stations

  Spring seasons ran from late April to the end of May or early June in 2026 · Chatfield (with Denver Audubon), Chico Basin Ranch (with Aiken Audubon) and Pineridge in Fort Collins

  Bird Conservancy of the Rockies lists three Colorado stations that band birds in spring. In 2026 Chatfield ran April 24 to May 31, Pineridge April 25 to May 30 and Chico Basin Ranch April 27 to June 6. The birds most often caught include yellow and yellow-rumped warblers, gray catbirds, Lincoln's sparrows and house wrens at Chatfield; Wilson's and orange-crowned warblers, Swainson's thrushes and brown thrashers at Chico Basin; and spotted towhees, white-crowned sparrows and house wrens at Pineridge. Those are the 2026 dates, and we found nothing yet for 2027, so ask the organization or the Audubon chapter whether visitors are welcome and when the stations will run.

• Broad-tailed hummingbirds and the Hummingbird Festival

  Hummingbirds are arriving through May; ask the city for the 2027 festival date · Mountain foothills, streamside meadows and feeders; the festival is at Starsmore Visitor and Nature Center in North Cheyenne Cañon Park, Colorado Springs

  The hummingbirds we followed back in April keep arriving through May, and the males' trilling wings are the sound of a foothill morning. Journey North takes hummingbird sightings from across North America and uses them to map the progress north each spring, and a first-of-year report from a Colorado yard helps. Colorado Springs holds an annual Hummingbird Festival at Starsmore; the city's page for the 33rd edition lists hummingbird talks, guided bird walks, a raptor talk with ambassador birds from the Pueblo Raptor Center, and crafts for children. That page did not give a date, so check with the city for 2027.

  A caution for anyone with a feeder: Colorado Parks and Wildlife treats bird feeders as bear feeders. See the safety notes before you hang one.

• World Migratory Bird Day

  The 2026 edition was May 9; the 2027 date was not yet posted · Worldwide, with Colorado events listed on the Colorado Birding Trail

  The international day for migratory birds is held twice a year, in May and October. The official site gave the 2026 dates as May 9 and October 10, and the Colorado Birding Trail's events page listed a statewide observance running from May 9 to October 10, 2026. Neither page showed a 2027 date when we read them, and secondary calendars disagree, so look at the official World Migratory Bird Day site for the confirmed day.

• The Ute Mountain Mesa Verde Birding Festival

  Annual, in early May; the 2026 festival ran May 6 to 10 and no 2027 date was listed · Cortez, in southwestern Colorado

  The festival bills itself as the only annual birding festival in southwestern Colorado, offering field trips around Cortez, and its proceeds benefit the Cortez Cultural Center. Registration is through the festival's own website. Because the dates move from year to year, check with the organizers before you book lodging.

What blooms in Colorado in May, and how far up the mountain has spring reached?

• Golden banner

  Opening in May, per Wild Ones · Part-shade spots in the foothills; look along trails and edges of woods

  Wild Ones' Front Range chapter calls golden banner a May arrival, with flowers of bright, sunshiny yellow, and notes that it can grow in part shade. Treat that as a rough window that shifts with elevation and weather.

• Pasqueflower

  April to June · Open slopes and meadows; Castlewood Canyon near Franktown is named as a place to look

  Pasqueflower is still in bloom through May at higher spots, and after the petals fall it makes feathery seed heads that are worth a second visit. A kneeling look at a pasqueflower is a good way to teach children that the smallest flowers are often the earliest.

• Star lily

  April to June, per Wild Ones · William F. Hayden Green Mountain Park in Lakewood is the place the chapter names

  The star lily is a white flower that sits right on a rosette of narrow leaves close to the ground. Because it is so low, look for it from a trail edge, and do not step off to photograph it.

Which young animals appear in Colorado in May, and what should I do when I find one?

• Elk calves

  Calving runs from late May into June · Mountain meadows and valleys; Rocky Mountain National Park is the best known place

  The park service says elk cows give birth from late May into June, usually away from the herd in tall grass or brush. A newborn calf weighs about 30 pounds and is spotted, and the spots fade by late summer. Most cows have one calf, a few have two, and the calf can join the herd about two weeks after birth. The park warns that cows are extremely protective and asks visitors to keep at least 75 feet away. If you come across a calf that appears to be alone, the mother is almost certainly nearby; back away and give the area a wide berth.

• Fawns and other hoofed young

  Late spring and early summer · Anywhere with deer, elk, pronghorn or moose

  Colorado Parks and Wildlife names deer, elk, pronghorn and moose among the species whose young are about now. Its advice for a fawn or calf is to take a quick look, leave it in place, keep pets away, and watch from a distance, ideally through binoculars, without getting so close that the parent will not return. Human handling can lead to abandonment, especially in deer, because a mother may not recognize a baby that smells of people. Elk and moose can become aggressive to defend their young.

• Fledglings on the ground

  From late May on · Lawns, trails and gardens

  A bird with its eyes open and feathers, hopping on the ground and unable to fly, is a fledgling, and its parents are still feeding it. The state agency says not to pick it up. A nestling with closed eyes and no feathers that has fallen from a nest you can see and safely reach may be put back, wearing gloves and a mask. Keep cats indoors, never touch a sick or dead bird, and be careful, since a parent bird may become aggressive near its young.

• Bighorn lambs

  Late spring and early summer · Steep, open and rocky country

  Bighorn sheep ewes gather with their lambs on steep, open slopes, and the lambs are easiest to watch from far off with a spotting scope. Treat sheep like elk and keep your distance, and do not feed any wildlife; Colorado law makes feeding wildlife illegal.

• Bats back at their summer roosts

  Spring migration; pupping season runs June through August · Eaves, porches, shutters, gutters and trees

  Colorado Parks and Wildlife says bats roosting under eaves, porch overhangs, shutters or gutters during migration are normal, and that if left alone they usually move on. The agency asks people not to seal bats out of buildings during pupping season, June through August, because pups can be trapped inside. Do not handle a bat; cover a grounded one with a box or can and call your local CPW office.

Is the high country open in May: Trail Ridge Road and Mount Blue Sky?

• Trail Ridge Road, Rocky Mountain National Park

  Usually around Memorial Day weekend (May 29 to 31 in 2027), but plowing and weather set the date · Estes Park to Grand Lake over 12,183 feet

  The park’s conditions page says the road usually opens around Memorial Day weekend. A National Park Service release from 2014, now archived, adds that the road climbs to 12,183 feet and that the Alpine Visitor Center sits at 11,796 feet. The earliest opening on that list was May 7, 2002, and the latest June 26, 1943. Crews begin clearing snow in mid-April from both sides, and in 2014 drifts averaged 18 to 22 feet. After it opens, the park has used night closures starting at 8 p.m. when daytime melting and nighttime freezing made the road hazardous. Above 9,000 feet the backcountry can still look and feel like winter in late May. The park posts road status online and on a recorded line at 970-586-1222.

• Mount Blue Sky and its mountain goats

  Summit road open Memorial Day through Labor Day only, per CDOT; the 2027 plan is not posted · Echo Lake to the summit of Mount Blue Sky, west of Denver

  The Colorado Department of Transportation’s byway page says the summit is open from Memorial Day through Labor Day only, that vehicle entry requires a reservation made through recreation.gov, and that the road from Echo Lake Lodge to the summit was scheduled to open on Memorial Day weekend 2026, weather permitting. The road climbs to 14,130 feet, which the department calls the highest paved road in North America, and the byway is known for its rock-jumping mountain goats above timberline. Check the 2027 reservations and opening date, and never feed or crowd the goats.

What is May weather like in Colorado, and what should I watch for?

• Severe storm season ramps up

  The threat rises quickly from about mid-May; tornado reports peak in early June · Mostly east of the mountains

  The Colorado Climate Center says the threat of severe thunderstorms and tornadoes in the state rises rapidly in mid-May, that average daily tornado reports climb through May and peak in early June, and that hail peaks later, in mid-June. Severe storms are far more frequent in eastern Colorado than on the Western Slope, because moisture and instability line up there more often. The center cautions that reports cluster near cities and major roads where people are watching. The Weather Service's advice is to turn on Wireless Emergency Alerts, carry a NOAA Weather Radio on trips without cell service, and know where you will shelter.

• Landspouts over Weld County in 2020

  An example from May 20, 2020 · Near Eaton and Greeley

  The Weather Service's Boulder office recorded six landspout tornadoes near Eaton and Greeley on the evening of May 20, 2020, all rated EF-0, with minor damage at three farmsteads and no injuries. It explains that a landspout is a narrow, rope-like funnel that forms under a growing storm cloud without a rotating updraft, along a boundary where two air masses meet, in this case a dry line. They are weak but real, and they show how the plains can turn from hot and gusty to stormy within an afternoon.

• Snow in the mountain stations

  May normals · Estes Park, Crested Butte, Telluride and Steamboat Springs

  NOAA's 1991 to 2020 normals put May snowfall at 9.5 inches at Estes Park, 6.7 at Crested Butte, 5.1 at Telluride and 2.8 at Steamboat Springs, against about 2 inches or less at the lower stations. A May storm that closes a high pass can melt in a day, and still count for the year.

When is the last spring freeze in Colorado, and is it safe to plant in May?

How much daylight does Colorado gain in May?

What is in the Colorado night sky in May 2027?

• Eta Aquariid meteors at new moon

  Active from about April 19 to May 28; peak night May 5 to 6, with May 5, 6 and 7 before dawn all good · Look toward the east before dawn, from a dark site

  The American Meteor Society puts the peak night at May 5 to 6, 2027, with the Moon only 2 percent lit, and Sea and Sky calls it an excellent year for this shower because the Moon is nearly absent. The new moon itself falls at 4:58 a.m. on May 6. For observers from the equator northward, the society describes medium activity, about 10 to 30 meteors per hour before first light. The shower's source point, in Aquarius, clears the horizon only a couple of hours ahead of sunrise from Colorado, so counts will fall short of what observers farther south enjoy; set the alarm for the final stretch of the night. Bring a blanket and give your eyes 20 minutes.

• Venus and Saturn close together at dawn

  Mornings of May 6 to 8; closest on May 7 · Very low in the east before sunrise

  By our own calculation, Venus and Saturn pass about 0.6 degrees apart on May 7, at a moment that falls in daytime, and sit within about a degree of each other on the mornings just before and after. Both sit in Pisces and very low: Venus rises only about an hour before the Sun, so at 40 degrees north they are only 3 to 6 degrees high 30 minutes before sunrise. Plan on binoculars and an unobstructed view to the east; this one is a challenge, not an easy catch. Venus shines at magnitude -3.9 and Saturn at about +0.7.

• Jupiter and the first-quarter Moon

  Evening of Wednesday, May 12 · High in the south after dark

  The first-quarter Moon sits next to Jupiter on May 12; our calculation puts the closest approach at about 3:52 p.m., in full daylight, so the pairing is one to enjoy later that evening. Jupiter, in Leo and Cancer, sets about 7 hours after the Sun on May 1, and Mars, in Leo, sets about the same time. The Moon passes about 3 degrees from Mars on May 13, also in daytime.

• The Flower Moon, a seasonal Blue Moon

  Full at 4:59 a.m. on Thursday, May 20; best evening is Wednesday, May 19 · Rising in the east around sunset on May 19

  The Flower Moon is the traditional name of May's full moon. The full instant falls before sunrise on May 20, so May 19 is the evening to watch it come up; Denver's moonrise that evening is about 7:59 p.m., by our calculation. Astronomical spring holds four full moons this year and this is the third, which older almanac tradition names a seasonal Blue Moon; Sea and Sky labels it that way. Under the newer rule that wants two full moons inside one calendar month, 2027 has none.

• Mercury's best evening of the year

  About May 12 to June 5; greatest elongation May 28 · Low in the west-northwest, 45 to 90 minutes after sunset

  Mercury swings farthest east of the Sun, 22.8 degrees away, at 7:14 a.m. on May 28, which makes the dusk of May 27 and May 28 nearly equal in quality. Sea and Sky calls it the best time to view the planet in the evening sky. On May 15, by our calculation, the planet drops below the horizon about an hour and a half (97 minutes) after the Sun and shines at magnitude -0.6; it then fades quickly through early June. These figures are for the central United States and shift by up to about 30 minutes elsewhere. Find a clear northwest horizon.

• The Milky Way's core after dark

  May 1 to 14 and May 25 to 31, when the Moon is out of the way · Low in the south to southeast, in the hours before dawn, from a dark site

  This is our own calculation, since no almanac publishes it: near 40 degrees north, those nights offer as much as about 3.8 hours of full darkness with the bright core at least 10 degrees up. The windows are computed for 95 degrees west and shift by at most a day across Colorado. Get away from town lights, and let your eyes adjust.

What can families do outdoors in Colorado in May 2027?

Safety notes for May in Colorado