These early September days have achieved that rare temperate equilibrium where neither air conditioners nor furnaces have anything to offer comfort aficionados like our cats. Thermometer readouts oscillate ever-so-slightly from high 60s to low 70s in the lulls between weather fronts, and we throw open windows on all sides of the house so it may breathe deeply with every shifting breeze. The cats lie on the sills leaning into the screens, nodding their noses around in the feral air to awaken their dozing hunter appetites. And we humans follow the dog outside onto the terrace to lie out in it… just for a moment before afternoon chores... just while we digest lunch.

So, it was in such a perfect supine moment of tracking my eye-floaters around the clear blue sky that a Monarch butterfly crossed the field of view and disappeared behind the peak of the house in a matter of seconds. It was the only Monarch I have seen all year. Was it really just a muted orange fritillary, which have been few and far between, but present nonetheless in the gardens this year? No, the black and orange stained-glass markings were clear even in my passing glimpse of the butterfly.

It used to be that Monarchs would crowd out all other comers on the buddleia “butterfly bush” in the terrace garden. Okay, not so much last year, but before that, they were plentiful. But this year, none appeared, until a perfect September day served one up… for just a few seconds.

 The precipitous decline of the Monarch butterflies has been well chronicled in the science pages of the popular press lately. Strangely, their struggle is being measured in acres. Early this year, The Washington Post reported on the recent annual fall migrations of Monarchs to the Oyamel fir forests in central Mexico, where they overwinter. In the decade between 2003 and 2013, the number of forest acres covered by the Monarchs has plummeted from 27.48 acres (hosting 556 million Monarchs) to 1.65 acres (33.5 million).

Conservationists cite three major causes for the alarming decline: degradation of the overwintering habitat in Mexico due to illegal deforestation; the destruction of breeding host milkweed plants through the expanding use of genetically modified herbicide-resistant crops in the American Midwest; and the recent increase in the frequency of extreme weather. The jury is still out on whether climate change brought on by human activities causes extreme weather, but clearly Homo sapiens has not been a friend to the Monarch butterfly in the 21st Century.

Apparently this wasting of other species is just something we humans do. September 1 this year marked the 100th anniversary of the death of the last passenger pigeon in a cage at the Cincinnati Zoo. Passenger pigeons were remarkably beautiful ruddy-breasted birds that once massed in flocks of three billion or more for their annual migrations. Commemorating the centennial of the passing of the species, John W. Fitzpatrick, writing in The New York Times last month, called it the most abundant bird ever to have existed. He observed, “We remember the passenger pigeon because of the largest-scale human-caused extinction in history.” A staple of 18th Century restaurants and dinner tables, the birds were hunted until just a tiny, unsustainable population was left.

None of us ever saw a passenger pigeon, but in knowing its story, we can understand that in this respect we have inherited a diminished world. I did see several Monarch butterflies last year and caught a fleeting glimpse of one this year. But what does this trend suggest? None next year? Have I just watched the last Monarch butterfly ever to visit my yard disappear over the peak of the roof?

Is it possible to ever experience that sense of perfect equilibrium again when the possibility of a Monarch butterfly alighting on the buddleia disappears forever? It is a thing of beauty — a small thing of beauty. Does its removal from the world tip the scales enough to prohibit perfection?

The answer, I suppose, depends how finely tuned our sensibilities are. Maybe we should be nodding our noses in the feral air like cats to awaken our appetite for the beauty of the world — even for the smallest things of beauty. Otherwise we may just unconsciously consign future generations to a world of diminishing resources, sparse beauty, and an unsatisfied hunger for something that was completely consumed by humankind’s coarser appetites before they were born.

(More than 90 other Field Notes essays by Curtiss Clark can be found at field-notebook.com.)