As you read this post, consider – how many of the life forms pictured here have you seen in your own yard? Assuming you even want them there, the chances are better the closer you live to a natural area with a diversity of endemic plants. All the animals in this post live at Beargrass Creek State Nature Preserve, a lovely protected fragment of forest. Their populations, though small, should be secure for the long term – but are they really?
Imagine you’re a female Cecropia Silk Moth, like the one pictured above. Though your species is not rare, it’s in decline, and in the small fragment you inhabit there are only a few of your kind. One spring night a male Cecropia flies toward your forest, tracking your scent with his long feathery antenna, but ends up at the bright lights of a supermarket parking lot and gets squished. It’s a bad year for parasites too, both endemic and introduced, which whittles the number of larvae that survive. (see link: http://northernwoodlands.org/articles/article/silk-moths). A nearby forest fragment is cut down, reducing the number of male silk moths that may visit your fragment. And one spring, during the few days of your short adult life, you and the other female silk moths living in the fragment aren’t visited by males. Since female silk moths are heavy with eggs, they cannot fly to find a mate. And that’s it – another local extinction.
We all know about habitat. Animals including us need food-water-shelter to survive, and if they have enough of the right stuff they’ll be ok, right? Theoretically a suburban one acre plot can be a wildlife paradise if it’s packed with habitat. Sadly it’s not so simple; this acre is likely an oasis in a desert of turfgrass and boxwood. It’s likely surrounded by a mowed edge infested with exotic (non-native) vines. This is the fragment problem; every natural landscape in the eastern US is a fragment, regardless of its size. At 80 plus acres (including adjacent natural areas) BCSNP is tiny. It’s hemmed in on all sides by a landscape mostly unfavorable, if not downright dangerous, to wildlife.
The story of the Eastern Box Turtle, Terrepene carolina illustrates the fragment problem well. This land turtle was historically so abundant that it has no particular adaptation for finding a mate, other than bumping into one. Although there’s an assumption that box turtles are abundant, research studies show populations are in decline across their range. http://www.iucnredlist.org/details/21641/0 The female in the pic above lives in a tiny fragment of forest, (20+ acres) behind the Passionist Earthand Spirit Center (PESC) in urban Louisville. She is one of only four turtles I’ve observed so far on this property; two male, two female (at least the gender ratio is good). How often has she had a chance to find a mate and actually lay eggs? It’s impossible to know, as box turtles are secretive about egg laying, and baby turtles are good at hiding. Females camouflage their nest sites so well they cannot be found visually. Unfortunately they can’t remove the scent; raccoons and other nest predators that are overly abundant in suburban environments destroy a large percentage of nests. If she leaves the forest fragment to find a dry sunny nest site there is the added risk of being crushed by a mower or a car, a common fate of box turtles.
The Box Turtles living in such a small fragment may each live more than 80 years, obscuring the fact that without young turtles entering the population, it will eventually die out.
Beyond the obvious physical danger to animals venturing out of their home fragment, there are more subtle risks to a tiny population of animals (or plants). As the gene pool shrinks, inbreeding may leave them less fit to survive disease and other environmental stresses. When a population declines to the point where reproduction is difficult, the chances of recovery are very slim.
The pics below are a small sampling of the animals that live at BCSNP. Countless others surely inhabit this tiny fragment, but these are ones I’ve been fortunate enough to see and get a picture of.
The Black Rat Snake Pantheropsis obsoletus, seems to be doing well at BCSNP, with more sightings of adults and young in recent years. I’m guessing the revival of the herbaceous layer, providing a diversity of plant seeds, has been good for the small rodent population. In this forest, sunny gaps with cut Bush Honeysuckle brush piles are popular places for Black Rat Snakes to hang out. The one in the pic above was feeling threatened when I closed in for a picture; it coiled, vibrated its tail, flicked its tongue and lunged forward with mock “strikes” like a rattlesnake. Leading me to wonder how often this harmless-to-humans species is assumed to be venomous.
Streamside Salamanders, Ambystoma barbouri, are nocturnal and reclusive, living most of their lives in underground burrows. This is one of two adults I’ve seen at BCSNP; I dug it up accidentally. It likely hatched from an egg laid in the small spring fed seep below, the only breeding pool I’m aware of in this forest.
Creatures that can fly, like insects, should be more widespread. But unless you have Greenbriar (Smilax) growing in your yard, you won’t see this strangely named caterpillar (pic below). It’s the larva of the Turbulent Phosphila moth, Phosphila turbulenta, which feeds only on Smilax leaves. They’re often clustered together in a visually confusing array; the prominent white dots on their rear draw bird attention away from their heads. Because deer love to browse Smilax, I take it as my job to “rescue” these vines when I find them yanked down and ravaged by browsing. Using a long stick, I lift the vine rope up to the safety of a high tree branch, where hopefully it will have time to grab on before the deer come back!
Though most insects can fly as adults, their larvae can’t and many have very specific habitat needs. The astoundingly sapphire Ebony Jewelwing Calopteryx maculata, is a predatory damselfly; its predatory larvae can live only in small, usually spring fed forested streams. Males compete with each other for the prime habitat areas of floating vegetation, on which females lay their eggs. This species is by no means rare, but since it’s only found by forested streams, it’s a treat to observe one. Fortunately, despite their small area, both BCSNP and PESC have good habitat in the form of small spring fed streams.
Even though adult insects can usually fly to new habitats, they are also at risk of vanishing from small fragments if the food source of their larvae goes away. The Spicebush Swallowtail larva in the opening pic is unbearably cute with it’s big fake eye spots. It’s a great poster child for promoting the planting of Spicebush and Sassafras (its only host plants in much of the Eastern forest). At BCSNP the population is thriving due in part to our focus on promoting Spicebush regeneration from seed. It’s now relatively easy to find a larva’s little silken shelter inside the curled leaf of a young spicebush plant, and the black and blue adults can be seen nectaring in a restored meadow and the LNC gardens.
Can frogs live in fragments? As you may remember from an earlier post ( 4/21 Frog at the Door) this unfortunate Grey Tree Frog Hyla chrysocelis, was dug up by me while planting. This mostly terrestrial species hibernates underground, only needing water for breeding. So it can survive in urban settings by laying eggs in fish-free backyard ponds, swimming pool covers and the like. In springtime, that occasional hoarse trilling in the treetops is a sign that tree frogs are courting.
The frog below likely doesn’t live at BCSNP anymore, as it was only observed twice, a few years ago, and no more of its kind have been seen. I’m not even sure of the species since this is the best view I ever got of it. But it makes the point that most frog species are long gone from this forest fragment, despite the fact there now seems to be decent breeding habitat in the form of seasonal wetlands. What happened to the frogs? Draining, creek channelization, followed by agriculture – any surviving populations were stranded in a desert of wetland-free urbanization. The fragment problem again…
In contrast, the habits of the Cave Salamander Eurycea lucifuga, allow it to thrive at least in some parts of this forest. An inhabitant of karst geology, this lovely orange creature spends most of its time in the “twilight” zone of caves, or under rocks and logs nearby. BCSNP has numerous small sinkholes and several year-round springs, indicating there’s good habitat for cave salamanders. The one in the pic was by the LNC front door early in the morning, after a night of hunting bugs under the porch.
But why are some species thriving in the changing landscape of the “anthropocene”? White tailed deer, coyotes, raccoons and possums have no problem with living in a fragment, or your backyard for that matter. These widespread, and still spreading species are habitat generalists, quick reproducers, and (except for deer), omnivores. So in a sense they’re pre-adapted for change, and find the food-rich environment of our cities a great new habitat to exploit.
In contrast, specialists have become highly adapted physically, behaviorally or both to a very specific habitat and niche (their role in the ecosystem), and can’t easily change. Unfortunately these species are usually the losers in the rapidly changing landscape of the “anthropocene”.
To illustrate the difference between a generalist and specialist species, consider the bizarre case of the Spotted Owl vs the Barred Owl. In most of North America, if you see an owl that looks something like the one in the pic below, it’s a Barred Owl, Strix varia. But it will have a “barred” pattern of feathers on its chest, not spots like the one in the pic. The pictured one, as you may have guessed, is its endangered cousin the Spotted Owl Strix occidentalis.
Thanks to the changing landscape, in the 1980’s Barred Owls began to show up in the Spotted Owl’s shrinking old-growth habitat in the northwest. The larger and more aggressive Barred Owl can easily oust its more mellow cousin from its specialized niche, not to mention interbreed with it. Two species could converge as a hybrid (reducing protection for old growth forests if the Spotted Owl isn’t an endangered species anymore). Either way, just one more nail in the coffin for beleaguered biologists trying to save the Spotted Owl. In 2012 the USFWS came to the ethically very uncomfortable decision to kill Barred owls living in Spotted Owl habitat by the hundreds. If you haven’t read the story, here’s a link: http://www.newsweek.com/2015/05/29/killing-barred-owls-keep-spotted-owls-breathing-332540.html
Will it work? Likely Barred Owls will have to be eliminated from the Spotted Owls’ habitat on an ongoing basis – the cards are stacked against this old growth specialist.
But I’d like to leave this post on a more hopeful note – the surprise in my yard this past week was a pair of mating Gulf Fritillary butterflies, Agraulis vanillae. This was followed by the female laying eggs on the many new shoots of Passionflower that have erupted all over our yard. Had it not been for climate change and the passionflower vine (and my casual approach to gardening) this more southerly butterfly would not have been there. (various Passiflora species are their only host plant).
For an in depth story about the new wave of Gulf Fritillaries and other insects, see this great blog link: http://jimmccormac.blogspot.com/2008/07/more-gulf-fritillaries.html
If you have passionflower in your yard, watch for “frits”. And if you don’t, plant some!