What to look for in nature in Wisconsin this May

When do warblers and other songbirds peak in Wisconsin in May?

• Horicon Marsh in the second and third weeks

  Peak variety tends to come in mid-month · Horicon Marsh (Dodge County and Fond du Lac County)

  The DNR’s account of the marsh calls late April to the third week of May the best time for spring songbirds, and says many warbler species arrive in the second and third weeks of the month. It also warns that once nesting begins, waterfowl are seen less often because females are on nests, and that nearly half the birds known to the marsh stay to raise young. The federal refuge keeps its three-mile auto tour open from March 16 until the day before the late-November gun deer season, and says the eastern gravel part of the Main Dike Road opens for driving to the fishing pier by May 15. Old Marsh Road is closed to hikers and bikers in spring and fall migration, so do not plan a May walk there.

• Floodplain forest on the Mississippi

  April and May are the best months for songbirds, per the refuge · Mississippi River floodplain refuge near La Crosse

  The refuge’s birding page says April and May give the best views of songbirds in the floodplain forest and marshes. Chestnut-sided, black-and-white and Cape May warblers and ruby-crowned kinglets pass through briefly, while prothonotary warblers and American redstarts stay to nest. It suggests scanning treetops from a boat landing or walking a floodplain trail, and listening at dusk for chimney swifts and common nighthawks over the river.

  Farther up the valley, Trempealeau National Wildlife Refuge notes that warbler watching is great in late April or early May from its observation deck, so a trip there in the first days of the month can catch the early wave.

• The Apostle Islands flyway

  Spring migration, with numbers that swing from year to year · Apostle Islands National Lakeshore, Lake Superior

  The National Park Service describes the islands as one of the heavily traveled migratory flyways of the Great Lakes region, because they shorten the open-water crossing for birds heading north of Lake Superior. Outer and Long Islands are important spring habitat for songbirds, hawks, falcons, waterfowl and shorebirds, and the park says counts swing widely between seasons, especially on Outer Island, and it suspects weather. Migrants make up more than 89 percent of the park’s breeding birds. Piping plovers nest on Long Island, with three to five successful nests a year from 2006 to 2020. The park advises that conditions on the lake are hard to predict and can change fast, so check current conditions before any crossing.

• Reading the migration forecast

  Tools run March 1 to June 15 · Anywhere in the state

  Cornell Lab’s BirdCast posts forecast maps of how much migration to expect and live maps of what radar sees in the air. Its spring tools are switched on from March 1 through June 15, and it names light and glass as dangers to birds flying at night. A calm, clear night with a south wind usually means birds overhead; the morning after a front is the one to spend in a park. Turning off unneeded outdoor lights on forecast nights is a small way to help.

What are whooping cranes, sandhill cranes and trumpeter swans doing in May?

• Whooping cranes at Necedah

  Eggs are normally laid from late April to mid-May · Necedah National Wildlife Refuge, Juneau County

  The Fish and Wildlife Service says whooping crane eggs are normally laid from late April to mid-May, usually two to a clutch, and that a pair may re-nest if the first clutch is lost early in incubation, though that has been documented only a few times. The Eastern Migratory Population was reintroduced from 2001 to 2010 and migrates between Wisconsin and Florida; the agency’s 2011 review found that none of the reintroduced populations were self-sustaining. Necedah’s visitor page says whooping cranes are often seen from the visitor center grounds and the Muskrat Loop, where scopes face the wetland, and that Goose and Sprague Pools offer drive-through viewing for loons, whooping cranes, sandhill cranes and trumpeter swans. Dawn and dusk are best. Many township roads on the refuge are seasonal or under construction, so call the visitor center at 608-565-2551 first.

• Sandhill crane colts

  Eggs hatch about a month after incubation begins; colts appear from late spring · Wetlands statewide, including Crex Meadows

  The DNR says sandhill cranes are back by March, build mound-shaped nests in wetlands with standing water, and usually lay two eggs. A colt that is still covered in down is too young to survive on its own, but colts leave the nest with their parents within a day of hatching, so a parent is probably close. Watch and listen for several hours before concluding anything, and call the DNR or a licensed rehabilitator for advice before touching it. At Crex Meadows, cranes return from mid-March to early April to build nests, and many pairs nest there each summer. The wildlife area asks that dogs be leashed from April 15 to July 31 and discourages motorized boats from April to June.

• Trumpeter swans on nests

  Egg laying runs from late April into June · Northwest, central and southeast wetlands

  According to the DNR, trumpeters arrive soon after ice-out and start nest building around mid-April. Egg laying runs from late April into June, with one egg every other day and a typical clutch of five. Incubation takes about 32 to 34 days, and cygnets hatch around June. The agency says water levels in suitable habitat matter in May through August, and the state population now exceeds 5,000. A swan sitting low on a muskrat house or a cattail island is on eggs; leave her be and use binoculars.

• Bald eagles raising young

  Nests active through the month · Every county

  DNR aerial surveys in 2019 found 1,684 occupied bald eagle nests, up from 108 in the 1970s, with active nests documented in every county. When you watch eagles, the agency says to heed closed-area signs and not to come so close that you flush them. A car makes a good blind.

Where can you see Karner blue butterflies and rusty patched bumble bees in Wisconsin?

• Karner blues on the lupine loop

  Late May is the first flight at Necedah · Necedah National Wildlife Refuge

  The DNR says Wisconsin habitats support the world’s largest populations of the federally endangered Karner blue butterfly. Necedah’s visitor page says the best time to look on its Lupine Loop, a walk of about 0.8 mile north of Goose and Sprague Pools, is late May and late July, matching the butterfly’s two broods. Karner blues can also turn up around the visitor center grounds, and the Karner Loop there is about 0.75 mile and accessible. These are small butterflies, about the size of a thumbnail, and they stay near wild lupine, so look low on sunny, still mornings and stay on the trail.

• Rusty patched bumble bee queens

  In southern Wisconsin queens typically fly from about April through May · Prairies, woodlands, marshes, farmland and gardens in the south

  The Fish and Wildlife Service listed the rusty patched bumble bee as endangered in 2017 and finalized a recovery plan in 2021. Queens leave their overwintering chambers in spring to start colonies, and the only documented overwintering queen in Wisconsin was found in 2016, under leaf litter in a maple-oak woodland. The agency suggests planting a mix of flowers that bloom from early spring through fall, leaving leaf litter and rodent burrows undisturbed, and uploading clear photos to BumbleBeeWatch, BeeSpotter or iNaturalist if you think you have found one.

Which spring visitors can you watch from a feeder or garden in May?

• Monarchs and hummingbirds returning

  First sightings are what volunteers report · Gardens and woodland edges

  Journey North asks volunteers for the first monarch adult, egg or caterpillar they find each season, and its hummingbird pages show how far north the ruby-throated hummingbird has come. We could not confirm a Wisconsin arrival date from an agency source, so use the maps instead of a calendar and report what you see. A feeder with plain sugar water is enough; change it often as the weather warms.

When do bats come back to Wisconsin, and when can you go into caves?

• Staying out of hibernation sites until May 15

  October 1 through May 15 · Caves and mines with bats

  Visitors are asked by the DNR bat program to avoid caves and mines housing bats from October 1 until May 15, so that hibernating animals are left to sleep. White-nose syndrome reached Wisconsin in 2014 and cave bat populations have declined significantly since then, though many little brown bat colonies have stabilized and some are increasing. Wisconsin holds a significant share of the surviving little brown bats in North America.

• Maternity season starts June 1

  Bat counts in early June and late July · Barns, attics, bat houses

  Bats should not be shut out of buildings from June 1 through July 31, while young are being raised. The program’s Great Wisconsin Bat Count asks volunteers for at least two counts of bats leaving a roost, one in early June and one in late July, beginning just after sunset and continuing about 40 minutes. May is a good time to find out where your roost is and plan the counts.

What changes at a Wisconsin marsh or woodland in May?

• Quiet water, busy edges

  Through the month · Marshes and ponds

  At Horicon, the DNR says waterfowl become harder to see once nesting begins, while songbirds, herons and others take over the foreground. Take binoculars and look for activity along the cattail edge at dawn. The refuge reports more than 300 bird species recorded at Horicon, with spring migration bringing a variety of waterbirds and songbirds.

• Hiking trails and wildlife areas

  Check before you go · Ice Age Trail and state lands

  The Ice Age National Scenic Trail runs 1,200 miles and is maintained largely by volunteers and partners including the DNR. The Park Service points hikers to its alerts page for conditions, so check there before a long hike. Trails near wetlands can be wet and buggy in May.

What can you see in the Wisconsin night sky in May 2027?

• Eta Aquariids

  The final dark hours of May 5, 6 and 7 · Aquarius, low in the east before dawn

  In 2027 this shower peaks right as the Moon goes new, so no moonlight interferes. For the peak, the American Meteor Society names the night of May 5 into 6, while SeaSky names May 6 into 7 and mentions up to 60 an hour, mostly for observers in the Southern Hemisphere. Since Aquarius, the radiant, clears the horizon just before sunrise this far north, Wisconsin watchers should plan on fewer meteors than the ten to thirty an hour quoted for the southern two-thirds of the nation. Choose a dark site with a clear view east and stay out until the sky starts to brighten. The Moon is a sliver, between 1 and 2 percent lit.

• Venus and Saturn before sunrise

  Around Friday, May 7 · Very low in the east before sunrise

  Venus and Saturn close to about 0.6 degrees on May 7, with roughly a degree between them the mornings before and after. They lie in Pisces, hugging the eastern horizon: at 40 degrees north they stand just 3 to 6 degrees high thirty minutes ahead of sunrise, and Wisconsin’s higher latitude puts them lower yet. A flat horizon and binoculars are essential. Venus is magnitude -3.9 and Saturn about +0.7. Think of it as a bonus for early risers.

• Flower Moon, with a Blue Moon label

  Full early Thursday, May 20; the Wednesday-evening rise looks round · Rising in the east at dusk

  By our calculations moonrise on the 19th comes near 7:53 p.m. at Chicago and 8:29 p.m. at Minneapolis, a span that covers the state. SeaSky also labels it a Blue Moon, as the third of four full moons squeezed between the first day of spring and the first day of summer. A tally by calendar month, which needs two fulls inside one month, finds none this year, so the label rests on the seasonal count alone. The full Moon is at 5:59 a.m. CDT, and its older name is the Flower Moon.

• Jupiter and Mars in the evening, the Moon beside them

  Quarter Moon beside Jupiter on Wednesday evening, May 12, and near Mars the next day · Southern and southwestern sky after dark

  Jupiter, among the stars of Leo close to Cancer, should, by our calculations, stay up late into the night at the start of the month, which makes it an easy target. The half-lit Moon sits closest to it on May 12 at about 4:52 p.m. CDT by our calculations, still daytime, so look that evening. About 3 degrees separate the Moon and Mars on the 13th. Mars has faded since winter and, by our calculations, sets near 2 a.m. on May 1.

• Mercury in the evening

  Evenings of May 12 to June 5, widest on Friday, May 28 · West-northwest horizon, 45 to 90 minutes after sunset

  For northern observers, this is Mercury’s finest evening showing of 2027. Mercury stands farthest east of the Sun, 22.8 degrees, at 8:14 a.m. CDT on May 28 (SeaSky says 22.9), which makes the 27th and 28th both fine evenings. In mid-May, at the center of the country, our calculations have Mercury going down about 97 minutes after the Sun at magnitude -0.6; it dims quickly once June begins. Choose a spot with an open western horizon.

• Dark-sky nights and the Milky Way

  Early and late in the month, away from moonlight · Low in the south before dawn

  From Wisconsin the galaxy’s brightest hub sits low over the southern horizon before dawn. Our calculations find moonless darkness with the hub up on the first fourteen days and the last seven at latitude 40 north. Up at latitude 48 north the windows shrink to the first eleven days and the last four, under two hours each, because nights are short. The state falls in between, so favor the first days of the month and the final few.

• Aurora

  Any clear dark night · Low in the north

  NOAA’s Space Weather Prediction Center keeps a 30-minute aurora forecast. Storms are possible on any night, but short May nights leave less darkness to see them in.

How mild, wet and thundery is May in Wisconsin?

• Severe weather season

  The peak tornado months are May through August · Statewide

  The Milwaukee-area forecast office reports about 23 tornadoes in a typical Wisconsin year, with activity centered on May through August and June the busiest. Most come between 3 and 9 p.m. The office adds that Wisconsin gets a few storms every year with hurricane-force straight-line winds, which prompt severe thunderstorm warnings, not tornado warnings. Know your county, know where your shelter is, and treat any warning in the afternoon seriously.

• Lightning outdoors

  Any afternoon thunderstorm · Trails, lakes, open fields

  The National Weather Service notes that anyone outside near a strike can be a victim of ground current, and that people who shelter under a tree to avoid rain risk side flash. Leave the trail or water when thunder is audible, and do not wait for rain.

• Late frosts

  Median last freeze runs from April 19 to late May · Garden and orchard

  The table below shows when the last freeze usually comes at the main stations. In the Northwoods the median falls in late May, and in about one year in ten the last freeze comes as late as the first week of June. Check the Wisconsin frost page for your own town before you put out tender plants.

How much daylight does Wisconsin gain in May?

When is the last spring freeze in Wisconsin?

What can Wisconsin families do outdoors in May?

• World Migratory Bird Day

  Held in May and October; check the organizer for 2027 dates · Local events and your own backyard

  At last look the organizers had listed just their 2026 events, one in each of the two migration seasons. The 2027 dates were not out yet. Watch the site, and ask local nature centers about events.

• Frog and toad listening

  Volunteers start in April · Ponds and flooded fields near you

  The DNR’s Frog and Toad Survey has run since 1984, with volunteers driving set routes and listening. A separate phenology survey asks anyone near water to listen at night for about five minutes and log what they hear. Sign up at the DNR survey page or by email to WFTS@wisconsin.gov.

• Bat counts and birdathons

  Early June and late July for bats · Barns, attics and bat houses

  Find a roost this month and plan to count in early June. The DNR lists the Great Wisconsin Birdathon as a way to support bird conservation; ask for its dates and format. The Wisconsin Society for Ornithology also runs field trips and lists them in its calendar.

• Log what you see

  All month · Home

  Journey North takes first sightings of monarchs and hummingbirds, and the DNR points birders to Wisconsin eBird for logging sightings and seeing recent ones. A notebook works too; many birders find their first-of-year dates drift by a week or two between years.

Safety notes for May in Wisconsin

• Spring turkey season

  Periods run April 21 to June 1, 2027 · Statewide, by zone

  The DNR lists the 2027 periods as the youth hunt April 17 to 18, then A: April 21 to 27, B: April 28 to May 4, C: May 5 to 11, D: May 12 to 18, E: May 19 to 25 and F: May 25 to June 1. Hunters need a license, a wild turkey stamp and a harvest authorization, and must register a bird by 5 p.m. the day after harvest. The DNR page does not list 2027 shooting hours and does not state a spring blaze orange rule; its only orange advice is general safety wording about wearing an orange cap or gloves on foot. If you hike in public hunting areas in early May, wear bright colors.

• Trout and other fishing seasons

  General inland trout season opens the first Saturday in May · Streams and lakes

  By DNR rule the general inland trout season opens at 5 a.m. on the first Saturday in May, which is May 1 in 2027, and runs through October 15. Wisconsin-Michigan boundary waters have been open since the last Saturday in April. The 2026-27 fishing year, effective April 1, 2026, listed walleye, northern pike and bass openers on May 2, 2026; the 2027 dates are not yet posted, so check the regulations pamphlet. Local rules can change dates for specific waters.

• Ticks

  Active through the month · Woods, brush, tall grass

  The CDC recommends repellent with an EPA registration number, boots and clothing treated with permethrin, and staying in the middle of trails. Afterward, shower within two hours, check your whole body, and run clothes through a hot dryer for ten minutes.

• Young animals

  Late spring · Yards and trails

  The DNR says a young wild animal’s best chance of survival is with its parents; many spend the day alone while the mother feeds or stays away to protect them. Contact a licensed rehabilitator if the parent is dead, a predator has attacked, or the animal is bleeding, thin, or covered in flies. Do not try to rehabilitate wildlife yourself.

• Cold water and weather

  All month · Lake Superior and the Great Lakes

  May air can feel warm while lake water remains dangerously cold. The Park Service says Apostle Islands weather is hard to predict and can change fast. Wear a life jacket, and check conditions before crossing.

• Memorial Day weekend

  Monday, May 31 · Lakes, campgrounds and trails

  Memorial Day falls on May 31, 2027, and the weekend usually draws the first big crowds. Book campsites and ferries early and leave wetlands and nests undisturbed.