It’s often the case when studying nature to have to rely on those things we can readily see to infer some information about things we cannot readily see. Let’s say that we’re out on a winter day looking for possible native prairie remnants. Unfortunately, much of the landscape is covered with snow and most of the plants we might hope to find are dormant, dried, and largely unrecognizable. Thankfully, a few, like pale purple coneflower, have durable seed heads that are large enough and tall enough to be visible above the snow even at some distance. Spotting a few of these on a little unplowed hillside is an indicator that at least some other native prairie plants are likely to be there under the snow. The site would be worth a visit the next summer when other plants, insects, and animals might be identifiable. The pale purple coneflower served as an indicator species for others that we couldn’t see at the time.

Sometimes animals and insects serve as indicators, too. Spotting a regal fritillary butterfly is a sure sign that somewhere nearby is a colony of fairly uncommon prairie violet plants. The prairie violet is short and might be easily overlooked even when in bloom. Its leaves alone would be all but invisible tucked in among taller plants in an early summer prairie. It’s the only food that regal fritillary butterfly caterpillars are known to eat, though. They’re strong and fast fliers (at least for butterflies), but the food plant that fed its caterpillar life phase can’t be too far away. Prairie violets tend to disappear in low quality remnants, so it’s possible that a fairly good quality remnant is nearby if we see a regal fritillary.

Seeing cowbirds in what might appear to be a fairly large unbroken tract of mature timber is a sure indicator that some form of disturbance is beginning to break up the forest’s integrity. They are a species of open spaces and forest edges. That forest may no longer be a safe nesting refuge for deep forest birds like scarlet tanagers, wood thrushes, and several varieties of warblers. The inverse is also true. Seeing no cowbirds is an indicator that a deep forest area may still be a healthy place for songbirds that need that habitat. It may be worthwhile to pursue additional protection for the area to prevent the kinds of disturbance that would encourage parasitic nesting cowbirds.

The temperature is projected to hit the 90s as today’s column is written. It’s the kind of weather that promotes algae growth in water with too much nutrient in it. Water with abnormally high concentrations of nutrient (nitrates and phosphates) may give rise to blooms of blue-green algae, now known as cyanobacteria, in addition to the more common green algae. Warm temperatures alone won’t cause algae blooms, but the presence of a blue-green algae bloom is a sure indicator of unhealthy nutrient levels even without additional testing. It’s also a sign for caution for swimmers and animal owners. Some species of cyanobacteria produce extremely toxic compounds that can poison animals (or people – especially children) that ingest the contaminated water.

Nature is a vast and diverse array of plants, animals, minerals, and more. Some of its components are big, showy, and easy to see, but most are all but invisible to us because they’re too small, too rare, camouflaged, or have very short life cycles when they’d be visible at all. Thankfully, years of study by generations of naturalists have pointed out a number of indicator species that can tell us much about the still largely unseen world of nature.