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Hearken! It's Spring. (Spring, 1990
Spring Courtship Baby Animal Orphans? Keep Your Eyes Peeled

Triggered by warming water temperature, amphibians emerge from hibernation ready for courtship. Hormonal production, which stimulates breeding behavior, is a response to water temperature, lengthening daylight, and renewed feeding. Male frogs and toads move to their home ponds, stake out a territory, and begin to call. Air sacs beneath the skin of the throat inflate to amplify the sound, which is made with the mouth closed. Vocalizations are species-specific, so females can locate males of the appropriate type amidst a cacophony of croaking. The calls of different species are also easily discernible to the human listener (see related article).

On a spring evening, settle down near a stream or pond, or drive any country road near a waterway and listen for the amphibian three-part harmony. Listening sites: Walden and Sawhill Ponds in Boulder; Walter Walker Wildlife Area near Grand Junction; the wetlands area around Deer Creek west of Chatfield Reservoir, south of Denver; the Russell Lakes and San Luis Lakes State Wildlife Areas in the San Luis Valley.

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While frogs and toads sing along the shores of the state's lakes and reservoirs, out on the water one of the most spectacular mating rituals of spring is taking place—the dance of the western grebes.

Grebe courtship resembles a ballet as the two long-necked waterbirds (they're neither ducks nor geese) glide serenely on the water's surface. The male and female (you won't be able to tell boy from girl, but the grebes know) begin by swimming directly at each other. Upon meeting they entwine necks, bodies circling in a slow pirouette. Gliding side by side like mirror images, the two flick their heads repeatedly to the side, then curl their long necks back to touch their wings. Finally, the two birds rise up together and run across the surface of the water.

You may have to watch this ritual in stages. Wait until you see two grebes swimming near each other, then settle down with your binoculars. The climactic scamper across the water's surface happens so fast that if you look after you hear splashing, you've missed it. Look for grebes on tree- or marsh-lined lakes where they build floating nests in the shallows, specifically Barr Lake State Park near Brighton; Highline Reservoir northwest of Grand Junction; the Monte Vista Wildlife Refuge in the San Luis Valley; Rifle Gap Reservoir near Rifle. Almost any large body of water at lower elevations is an appropriate site to look for grebes.

An equally enthralling courtship dance is performed by the greater sandhill crane. Each spring, on their way to northern nesting grounds, thousands of the large, red-capped wading birds gather in the San Luis Valley, where they dance with seeming abandon to a wild and mystical love song only they can hear. Bowing, hopping, dropping their wings, then leaping high into the air, not only pairs of birds but sometimes hundreds dance at the same time. And the cranes don't just dance in silence; they try to attract attention to themselves with loud calls. Associated with each call is a stereotypical movement in the dance. Above the dancing flock echoes a riot of trilling and calling, making for a very social event.

The 1990 Monte Vista Crane Festival is scheduled for March 24-25, but the birds may be seen in the Monte Vista area into April. If you see a white crane among the flock, you will have been lucky enough to spot one of the few foster whooping cranes hatched in sandhill crane nests. Biologists estimate that although the whooping crane population has reached about 200 birds, only thirteen whoopers currently survive of the eighty-five foster fledglings hatched since 1975. For information, contact the Monte Vista National Wildlife Refuge at 719/852-4382.

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While the frogs are singing and the birds are dancing, the spring-breeding mammals of Colorado (primarily rodents and small animals with short gestation periods) largely dispense with the finesse of courtship. Except for some chattering and chasing around, mammals seem to get right to the point.

Though solitary most of the year, male Abert's squirrels congregate during spring in the vicinity of a female's nest. When she appears, the dominant male approaches her, followed by the subordinate males. Then begins a "mating chase". She runs on the ground, and the males follow at a distance. She jumps on a tree trunk and freezes; they freeze about a meter away. She moves; they move. This goes on all day as the female becomes more receptive to the males. Although posturing and vocalizing are indistinguishable from standard squirrel alarm behavior, if you see a mass movement of tufted-eared squirrels among the ponderosa pines, you're probably witnessing the Abert's dating scene.

Another resident of the pine forest, the female chickaree or pine squirrel, has little taste for romance. Usually highly intolerant of the males of her species, she is receptive to mating for only one day each spring. On that day, the female chickaree will cease her angry scolding and allow males into her territory. So listen for silence; when the pine forest grows quiet this spring, for heaven's sake don't interrupt! Abert's squirrels are found in forests of mature ponderosa pine; the chickaree live among mixed spruce, fir, and pine forests throughout Colorado.

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With a good ear, you can distinguish the different amphibian voices calling on a spring evening.

1. Northern cricket frog—this voice sounds like two stones clicking together.
2. Chorus frog—sounds like someone running their thumb down the teeth of a comb, rising in pitch.
3. Leopard frog—a low sound like a motorboat, mixed with chuckling and grunting.
4. Spadefoot toad—a brief, distinct, duck-like sound.
5. Western toad—a soft chirping, like the cheeping of a baby chick.

Next: Baby Animal Orphans?

(The information contained in these issues of Colorado's Wildlife Company was accurate at the time of original publication. Situations and circumstances described, staff positions, contact information, and dates of some events may have changed in the interim. Present knowledge and understanding of biological and behavioral facts and information may also be different, now, than presented here.)