Birds and other things bring early signs of spring

With lakes and rivers still mostly frozen, it may seem overly optimistic to think of spring. But it’s coming.

Days are getting noticeably longer, and that’s the key. Photoperiod is nature’s only absolutely reliable timepiece. I’m hopeful that we’ve seen the last sub-zero and single-digit temperatures. In spite of frigid temperatures and enduring snow cover, longer days trigger hormones that compel birds to advertise their presence.

On February 19th, when the thermometer soared to eight degrees above zero, Carolina chickadees and white-throated sparrows sang as I filled the feeders. Over the next several days, cardinals, titmice, bluebirds, and song sparrows joined the chorus. Other early signs of spring are absolutely predictable.

Bald eagles

Bald eagle nests in the mid-Atlantic states already have eggs, and incubation is underway. After 35 days, the first eggs will hatch in late March or very early April. Though many eagle cams can be found online, a high definition camera is trained on an active nest in south-central Pennsylvania at www.pgc.state.pa.us. Click on the “Bald Eagle Live Stream.”

Falcons

In about two weeks, the first eggs will appear in urban peregrine falcon nests. Links to falcon nests in Pittsburgh can be found at the National Aviary’s web site, www.aviary.org. Click the “Conservation” icon, then click “Pittsburgh Area Live Nest Cams” in the dropdown menu.

Wood frogs

I expect to hear wood frogs sing sometime this week. Sounding like muffled quacking ducks, they will just have thawed after having spent the winter frozen solid. It’s true that wood frogs survive even the coldest winter temperatures. When living tissue freezes, ice crystals form, cells rupture, and the organism usually dies.

But in the dead of winter, wood frogs freeze solid. The body is rigid, breathing ceases, and the heart stops beating. And yet, when winter thaws, they revive. Wood frogs have perfected the cryogenic freezing process. In winter, almost half of the frog’s body may freeze and turn to ice. Freezing is made possible by specialized proteins and glucose, which prevent intracellular freezing and dehydration.

Skunk cabbage

In low spots where seeps abound, look for skunk cabbage to emerge. Its own metabolic thermogenesis provides the heat needed to push through snow. Rapidly growing skunk cabbage flowers can maintain a “body temperature” as much as 30 F higher than ambient temperatures. The growing skunk cabbage flowers generate heat via oxidation. This requires an unusually high rate of oxygen consumption for a plant. In fact, it’s comparable to the metabolic rate of a hummingbird.

The purpose of the heat is twofold. It produces the chemical odors that mimic decaying flesh and attract insect pollinators. The plant’s body heat also warms the air within the flower, and this rising current carries with it the pungent odor of the plant.  Think of it as a mini-thermal, similar to those that carry soaring hawks and vultures, only this one just carries aromatic molecules. Watch for a variety of tiny pollinating bees, flies, and beetles attracted by the odor as they visit skunk cabbage on mild late winter days.

Woodcock

At these very same seeps or wet spots in slowly thawing meadows, I expect to hear the evening “peents” of displaying woodcock that have just returned from points south. On a moonlit night, I might even catch their distinctive sky dance in silhouette.

Woodcock are plump, quail-sized migratory birds that weigh six or seven ounces. Though classified taxonomically as shorebirds, woodcock live in damp, lowland woods.  They usually return in late February, but I can always count on them in March. Woodcock “dances” peak at dusk and dawn from early-March through early May.  Males are promiscuous; they mate with any hen that finds the dance irresistible.

Hummingbirds

Finally, though I don’t expect ruby-throated hummingbirds to return until mid to late April, the year’s first hummers have already returned to Louisiana and Florida on Feb. 22. Though I hang a nectar feeder on April 15, I realistically don’t expect to see the first hummer until after April 22. Follow their progress north at www.hummingbirds.net/map.html.