Notice the days getting shorter? You’re not the only one. Honking geese gathering in v-formation, flocks of birds fattening up on seeds and berries, and, as we noticed on our walk in Curtis Prairie today, several otherkinds of animals getting ready for their migration. We saw floating amongst the prairie grasses about a dozen or so monarchs highlighting the blooms and feeding on numerous sawtooth sunflowers (Helianthus grosseserratus), prairie or pasture thistle (Cirsium discolor), and rough blazing-star (Liatris aspera). On one prairie thistle we saw several species of bumble bees working their way around the blooms into the small tubular flowers as a ruby-throated hummingbird appeared, adeptly hovering into position to capture the nectar on the unoccupied side of the flower.
Hormones are to thank for this burst in activity in the monarch and the hummingbird populations. They’re sensing and responding to the seasonal changes that will impel them to gather the needed extra nourishment as they prepare for a long journey. This generation of monarchs are special. The signals they gather from the environment will tune their hormones and activity for upwards of a 3,000-mile journey (depending on where they start) to a well-defined area of mountaintops in central Mexico. While summer generations of monarchs typically live for two to six weeks as adults, adults in the migratory generation can live for up to nine months. Most monarch butterflies that emerge after about mid-August in the eastern U.S. enter reproductive diapause (do not reproduce) and then migrate south to overwintering grounds where they have never been before. In the spring, this all changes—internal and external cues will result in this generation mating and egg laying. Then, successive generations will carry on the journey north for the summer.
It was heartening to see so many monarchs. Many of us sense that we are seeing fewer of them than we have in previous years. That is probably true. However, people ask all the time whether or not a particular bird or animal is in decline if they had seen many of them at one time and now they are not. Oftentimes, it is true that there is a population decline. However, it is difficult to get an idea of population trends based on our usual habits of being outdoors, often on an erratic basis, and usually in a somewhat limited area. The populations may be in a natural or temporary cycle of recovery and decline. They could also be shifting as a result of resource availability or some other choice or random event.
In the case of monarchs, most of us had heard in the news that there has been a steady decline in the population. Indeed, there have been many systematic counts and studies. One of the most interesting findings has been that the populations that make it to central Mexico are surely in decline. However, as this population breeds its successive populations, these adults and their offspring do fairly well. These successive generations that live several weeks are successful as they make their way up north in the continental U.S. and into Canada. So there is a rebound or recovery.
Yet each year for several decades there has been a decline in the overwintering population (there may be some slight recovery in recent years). This trending and dramatic decline has led researchers to focus on lack of late-summer/ fall nectaring sources for the monarchs traveling south on that 3,000-mile journey. A case for more prairie and fall plantings? Most agree that this theory—a lack of late-summer/fall nectaring sources as the major factor in driving population decline—warrants further investigation. And ecologists don’t want to minimize the fact that there is habitat disruption and destruction all along the way throughout the spring, summer, and fall. All these factors, including fewer milkweeds—the host plant to the eggs and caterpillars of the monarch—fewer nectaring plants for the breeding and migrating adults, and habitat fragmentation and destruction, especially their wintering habitat, all are stressors on individual monarchs and the overall population.
While the monarchs were noticeable, there were several plants on the prairie that were so dominant we were compelled to ask what was going on with them. We saw a sea of bright yellow Canada goldenrod (Solidago canadensis) and broad patches of sawtooth sunflower (Helianthus grosseserratus). The dominant shrub is gray dogwood (Cornus racemosa). The dogwood has interesting shades of purple and red leaves at this time of year as the chlorophyll subsides. These three dominant plants all do have some things in common: they all produce lots of seeds, and they can also reproduce vegetatively. The sunflower and the goldenrod will send underground shoots from the stems and form clones. Similarly, the dogwood will send up suckers from its underground roots and form clones. In my small prairie garden at home when I see goldenrod taking over, I’ll do lots of pulling and chopping down to exhaust the plants and give the other plants a chance to seed and spread. In the larger prairie, we usually let the seasonal burns and changes in moisture and soil conditions help to spread things around and provide some competition to keep a variety of plants growing in the prairie. Less dominant were the spiky bright purple flowers blooming on very short stems along a roughly three-foot-tall plant called rough blazing-star (Liatris aspera), and another goldenrod, stiff goldenrod (Solidago rigida). The flowers of stiff goldenrod are similar to the Canada goldenrod, tightly packed bright yellow in clusters at top of the plant. However, the stiff goldenrod (averaging about 3 feet) is shorter than the Canada goldenrod (about 5 feet) and has stiff thick, egg-shaped leaves tightly clinging to the stem in an upright orientation. The Canada goldenrod has long lance-shaped leaves that lace out from the stem.
Although the Canada goldenrod isn’t something we plant or encourage to grow, it is amazing to see the myriad of wasps, bees, aphids, and beetles feeding on the flowers. We were also pleased that the steady breeze kept most of the mosquitoes from locating their favorite meal—our blood. But when we or the breeze stopped long enough, we were reminded that the mosquitoes were still around in force. There is still standing water here and there, and mosquitoes are and will be emerging for a while. Some small drab-looking goldfinches also noticed the standing water and came for a drink. The goldfinch is the latest nesting bird in this area. They will build small nests among the shrubs in August. They will take advantage of the short, soft, downy feathery plumes, called pappus, which are attached in a parachute-like fashion to spread the seeds of thistle, wild lettuce, goldenrod, and a few other plants available at this time in late summer, as a soft lining for their nests. And they also eat the seeds.
The goldfinch chicks are ready to leave the nest about 12 days after they hatch. However, they will stick around the parents for protection and to beg for food for three weeks or so. Some very small drab goldfinches stood out in contrast to the larger birds, especially some of the males who still were showing fairly bright yellow and black plumage. We wondered if some of the very small goldfinches were this years’ new youngsters drinking from some of the puddles still in the prairie today.
Also visible along the trail, for fleeting moments here and there, were chipmunks and mice. As if on cue, we heard the clear single note of a circling red-tailed hawk. I pointed out the tall trees on the edge of the prairie where hawks and owls will perch as they watch and circle the area in search of their meals: these small rodents, and some of our larger rodents and rabbits.
The soundscape on the prairie today was predictable—lots of high-pitched chirping along the roller coaster–like flights of the goldfinches (probably “contact” calls, keeping track of the flock); gray catbirds calling here and there amongst the shrubs; and, some very loud patches of calling male meadow katydids and crickets.
The amount of plants in bloom will be decreasing, but interesting fall colors are already on their way—big bluestem is beginning to show its variety of hues, and some of the sumac is turning color and will show some bright reds soon.