Summer #10: Predators

female_sharpshin.jpgLast Sunday morning I was on my way out to fill our surprisingly quiet, front yard bird feeders. Usually there are dozens of birds (cardinals, titmice, chickadees, house finches, and mourning doves) noisily feeding on the black oil sunflower seeds, but this morning there were no perching birds and no ground feeding species to be seen. I looked out my living room window just as I opened the front door and saw the reason why: a female sharp-shinned hawk was perched on a low branch of the side spruce tree probably taking a short rest after swooping through the front feeder area.

Sharp-shinned hawks feed almost exclusively on smaller birds. From the evidence I have seen around my yard (piles of feathers under well hidden roosts) mourning doves are their preferred prey, but cardinal feathers are also frequently parts of these feather middens). Deborah and I have watched this particular female sharp-shin for several years. We have videoed her mating calls and dances with her smaller mate, kept track of her regular hunting circuit around our yard and fields, and even listened to her interactions with her fledglings. She is a valued member of our Rose Street ecosystem. She also kills many of the birds whom we equally admire and value. There is, then, a conflict here that needs to be examined both emotionally and intellectually.

By setting up and maintaining a bird feeding station in our yard, we have created not only a resource for our seed eating birds (and the cardinals and the house finches have responded to this bounty again this year with a fourth mating!), but we also set up a “hawk feeding” station for sharp-shins and also for the occasional red tail hawk. This predation seems cruel and vicious. The emotional reaction is one of revulsion at the blood and death and anger at the “cruel” predator. But the reality of this system is very different.

When a sharp-shinned hawk attacks a flock of feeding birds the usual outcome is dispersal of the potential prey and no kill for the hawk. The few times that the attack is successful, the captured bird is most likely one who was slower than his flock mates or less aware of their surroundings. The captured bird, then, was “less fit” than the birds that escaped from the predator. This on-going selection has a profound impact on the quality of the prey species and represents one of the main evolutionary impacts of predators on their prey. Over time, predators cull out less fit prey individuals and this leads inevitably to better and better quality in the prey population. This has been observed in Yellowstone with vast, measurable improvements in the elk herds with the introduction of wolves, and this is also going on in my front yard bird feeders with the sharp-shins culling the populations of the song birds. Predators also keep prey populations from growing past their resource bases. Predators also keep many pest populations (everything from mosquitoes to mice and rats) under control.

Predators, though, are not well loved by humans! Wolves, mountain lions, rattlesnakes and even eagles and hawks just to name a few, have been regularly and systematically exterminated because of our emotional reactions to their feeding behaviors. The consequences of the loss of these predators on their prey populations have been severe.

We have other predators about us, too. Just a few days ago I helped a four foot black snake safely cross Rose Street knowing that if I didn’t stand guard over him someone would be very likely to either accidentally or intentionally run him over. This snake is an accomplished predator of mice and rats, and I valued his potential control over these populations. Also, our basement is full of spiders and no one in our house is allowed to kill or displace any of these important predators. One new benefit of this predator protection is the observation that Deborah and I have recently made of dry, spider-eaten, marmorated stink bug carcasses in piles in and under the basement spider webs. Our predators are helping us control those invasive pests!
            
Nature is sometimes not kind or pretty, but it represents a system that is constantly regulating and improving itself. We bring ideas of “good” and “bad” to our observations of Nature and need frequently to step back from our biases to see the quality of the real system.
 

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