Last week I wrote about my Backyard Siskin Invasion, the influx of about 40 Pine Siskin birds to my bird feeders. This week nature did what it does best. It tried to balance out the ecosystem and ensure that a given species doesn't spend too much time in one place and overrun the local food supply. It did so by introducing a predator into the mix. Not just any predator, but a keystone predator.
We initially saw an American Kestrel fly through the yard, chasing the Pine Siskins and House Finches, then this Sharp-shinned Hawk showed up and perched in the yard. The Sharp-shinned Hawk is demonstrating its signature squared off tail with a central notch.
The presence of the bird feeders in our yard modified the behavior of the Siskins by attracting them to the yard. The presence of the Siskins modified the behavior of the Hawk by drawing him to our yard. Now the presence of the Hawk has modified the behavior of the Siskins. They still come to eat, but spend less time and are likely much more alert. This is a small example of how nature operates.
It fascinates me that people believe that the absence of predators can be a good thing. Repeated studies have shown that prey species are healthier in the presence of predators. That the Trophic Cascade of the effects of keystone predators down through the food chain can have dramatic positive effects throughout the ecosystem and help the ecosystem to better respond to other stresses. The foundations of this concept have been known for 150 years, but our policies still reflect an absence of understanding.
Regardless, it is wonderful to have this brief and intimate view into the process at work.
Update 1/25/2008: This afternoon we had an American Kestrel fly through then a hour later two Sharp-shinned Hawks arrived! They stuck around the neighborhood for close to an hour.
Update 2/7/2008: This article featured in I and the Bird #68 blog carnival. "I and the Bird remains the undisputed champion of blog carnivals concerning birding and wild birds on the planet. Our far flung collaboration is still the best way for nature bloggers everywhere to reach an engaged, intelligent audience." - Mike Bergin, Founder of "I and the Bird".