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May 21 - 31


Racine has 15 hours and 6 minutes of daylight and Superior has 15 hours and 35 minutes of daylight at the end of the period. Southern Wisconsin gains 18 minutes of daylight and northern Wisconsin has 21 minutes more than the previous period.


























Bird migration: Late-May has bird migration mostly winding down. Almost all of the land birds are on territory. The peak of warbler migration has passed for most species, but a few species peak during this time frame and others are still lingering in the woods. In addition, cuckoos, which feed mainly on caterpillars, arrive to start the feasting on new emerged fuzzy caterpillars. Most of the peak migrants are tundra nesting shorebirds, which makes sense, because their summer habitat is still frozen solid until June. The following table highlights those species, whose peak migration numbers occur during late May.


Table 1. Bird Species with Peak Migration Numbers, May 21 – 31.























Late-May wildflowers: Late-May is a great time to visit rich woodlands, but also visits to prairies, and northern barrens can be rewarding. The spring floral display is still going strong with many species reaching their peak intensity. Some of the early species such as spring beauties may be setting seed and withering. Whereas, other habitats, like open bogs are just starting to display colorful flowers. The Northwoods, predictably is a little later and many of the mid-May bloomers from the south are now in full bloom in the northern forests and meadows. Sedge Meadow and barrens areas should not be overlooked, as several interest species bloom in May. The following table indicates some of the more common species to be expected on your ventures.


Table 2. Native Wildflowers with peak blooming times May 21 – 31


















































Lepidopteran activity continues to increase: Plants in the woods and fields grow rapidly during May, thus providing food for many moth and butterfly species. Most of these species do best in summer and early fall. There is, however a contingent that does best earlier in the growing season. The following table lists a few of the more recognizable species, their habitat and larval food plants. One species on the list, the Karner blue butterfly, is a federally-listed species. This species is considered rather rare in the world, but it can be relatively common in “pine barrens” areas of the state from Waupaca to Burnett Counties.  


Table 3. Large and more recognizable Lepidopterans whose flight period either starts in late-May or is limited to this time period.


































Slender glass lizard: The slender glass lizard is a legless lizard with a long slender body and tail. It can grow to almost 30 inches in length. The tail is nearly 2/3 of the bodies length. The general body is a bronzy -tan with a dark brown band running down the middle of the back. Slender glass lizards are often mistaken for snakes, but can be distinguished ear openings, and moveable eyelids. This is Wisconsin’s only legless lizard.


These lizards are threatened in the state due to very restrictive habitat needs and habitat loss. They inhabit savannas, barrens and oak woods, but need to have very sandy soils in which they can burrow. This species can also survive in sandy roadsides if they are not maintained with frequent mowing. Their preferred habitat, sandy oak savanna has been drastically reduced in the State and is now limited to widely scattered location in the central sands. .


Slender glass lizards spend most of their time underground. Even during times of peak activity, only a small percentage of the population is on surface. These periods of activity vary by season: aboveground activity spikes in late May and early June and again from late July to early September. A naturalist should consider luck on their side, if they find one. It is best to simply observe, if they are captured, they may lose their tail. This discarded tail will break into many smaller wiggling pieces, thus the name glass lizard.


Bullsnake: The bullsnake is our largest snake reaching 6 and 1/2 feet in length. They are large constrictors that feed mostly on rodents with pocket gophers being a favorite prey. They inhabit sandy prairies, oak savanna and barrens, oak woods and pine barrens. They hibernate in rock crevices with blue racers, timber rattlesnakes and gray rat snakes and emerge from hibernation in early May. Naturalists’ best opportunity for observing bullsnakes is in mid- to late-May, when they are mostly on the surface and either looking for mates or fending off competing mates. They preform twisting duels to get the upper hand on rivals. After June, the bullsnake is very difficult to observe, since they are mostly underground in rodent burrows.



  • Green frogs reach their peak vocal intensity in southern Wisconsin. It will be a few more weeks before peak calling occurs in the Northwoods.

  • Red-backed Salamanders become active in the forest debris layer. Highest numbers of these salamanders are near ponds in old-growth forests.

  • Red cedar cones (also incorrectly called berries) start development.

  • Moose calves are usually born during this time period.

  • White pine pollen usually reaches its peak during this time frame. The stick yellow stuff can cover cars and roofs, and unfortunately can be allergic to some people causing extensive cough fits.

  • As the pollen falls in the north, eastern cottonwood sheds its seeds mixed in with light wispy cotton farther south. These “cotton falls” usually occur on days with lighter winds and can appear like snow on the warm breezes.

  • The pine barrens and dry pine forest have bracken fern fiddleheads everywhere.

  • Fish species spawning in Wisconsin’s rivers and streams at this time are common carp, bullhead species, white bass. Although, all of these species may spawn earlier or later depending on water temperature in any one given year.  

  • Toothed herrings are a family of fish little known in the state. The mooneye and goldeye are big river fishes. They are migratory species that survive the winter in deep pools than migrate to spawning areas in May. These migrating fish can occasionally be seen in larger river especially the lower Wisconsin and lower Chippewa Rivers.

  • At the end of the month keep an eye on small clear streams for the first emergence of the ebony and river jewelwing damselflies. These two species are our most endearing damselflies, because they are iridescent black and green coloration. They slowly work along these placid streams making observation easy.


Eared Grebe

Black-bellied Plover


Ruddy Turnstone

Red Knot


Semipalmated Sandpiper

White-rumped Sandpiper

Baird's Sandpiper


Black-billed Cuckoo

Yellow-billed Cuckoo

Cedar Waxwing

Connecticut Warbler

Mourning Warbler

American Pipit



Prairie potholes

Mudflats/upland short grass

Great Lakes bays and sand spits

Mudflats/upland short grass

Mudflats/upland short grass

Great Lakes bays and sand spits



Mudflats/upland short grass


Deciduous woods

Southern woods and floodplains

Shrubby areas with fruit

Shrubby thickets

Shrubby thickets

Mudflats/upland short grass

Open grassy areas




L. Michigan & Superior


Rare and decreasing

L. Michigan & Superior






More common south





More common south

Common Name

Wild geranium

Red-osier dogwood

Wild columbine


Spirea - white and red

Green dragon

Clintonia or bluebead

Canada Mayflower

Dwark lake iris

Mocassin flower

Wild lupine

Bog white violet


Black cherry in the north

Robin's plantain

Yellow wood sorrel


Highbush cranberry

Blueberries (2 species)

Baneberries (2 species)

Hairy puccoon

Cream baptisia

Seneca snakeroot

Indian paintbrush


Wild yam (starts blooming)

Prairie smoke seeds

Prairie turnip

Dwarf ginseng

Spring forget-me-not

Virginia waterleaf

Great waterleaf



Nodding Trillium


Swamp currant

Small white violet

Arrowleaf violet

Sand violet






Dry to moist woods

Wet meadows

Dry to moist woods, cliffs


Wet meadows

Floodplain forest

Dry to wet conifer forests

Dry to wet northern forests

Boreal forest - Door County

Dry to wet conifer forests

Barrens and savannas

Wet conifer forests

Acid bogs

Dry to moist woodlands


Roadside, fields, trails, gardens

Woods and edges

Wet shrubby areas

Sandy barrens to acid bogs

Dry-mesic to moist woods

Sandy barrens and prairies

Dry-mesic to wet-mesic prairies

Dry prairies and savannas

Moist meadows and prairies

Moist woods and prairies


Dry and sandy prairies

Rare on dry-mesic prairies

Rich wet-mesic forests

Dry woods in the central sands

Rich woods

Rare in rich woods

Rare in mesic woods

Cedar Swamps

Dry to rich forest in Northwoods

Rare on old-growth cedar swamps

Wet forest esp. north

Wet forest and bogs

Sandy barrens and rock outcrops

Moist sand in the central sands

Dry prairies and savannas

Northern bogs

Northern bogs

Sandy and rocky conifer forests


Giant swallowtail (1st brood)

Canadian tiger Swallowtail

Mustard white (1st brood)

West Virginia white

Silver-bordered fritillary

Karner blue butterfly

Freija fritillary

Monarch (first arrivals)

Juvenal's Dusky-wing

Sleepy Dusky-wing

Dreamy Dusky-wing

Horace's Dusky-wing

Mottled dusky-wing

Columbine Dusky-wing

Wild indigo Dusky-wing

Persius Dusky-wing

Pepper and Salt Skipper

Cobweb skipper

Falcate orange tip

Frosted elfin

Brown elfin

Western tailed blue

Spring azure

Red-disked alpine

Chryxus arctic

Eight-spotted forester

Great ash sphinx

Canadian sphinx

Anna tiger moth

Tufted bird-dropping moth

Snowberry clearwing


Floodplains and old pastures

Mixed forest edges

Clearings in forest

Clearings in forest - Northeast WI only

Sedge meadows and bogs

Sandy pine barrens

Leatherleaf and spruce bogs

old fields, meadows

Oak woodlands

Oak barrens

Dry prairies

Roadsides and barrens



Open woods

Open barrens and marshes

Glades and streamsides

Pine barrens and oak savanna

Open streamsides in far southern WI

Pine barrens and oak savanna

Barrens, bogs, conifer woods

Northwest barrens

Deciduous woods

Open bogs in the far north

Meadows, open grassy and rocky areas

Woods and floodplains


Open woods

Open areas



Larval food

prickly ash

aspen, birch, cherry

cress species



wild lupine


milkweed species






basswood and oaks

Wild indigo and lupine

Wild lupine




Wild lupine



Dogwoods, viburnums


Poverty oat grass

Grapes and Virginia creeper



Clover and plantain

Hawthorns and grapes


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