Now that the post title has your attention let's talk woodpeckers. This male Pileated Woodpecker came to the feeders at lunch on last week. The sunshine has been beautiful and welcome. This same bird has been hitting the suet feeders pretty much every day in this cold weather. In my experience, the pileated woodpecker is the shiest of all the woodpeckers we have in Minnesota. I can stand at the window and watch downy, hairy and red-bellied woodpeckers as they feed and they don't seem to care about my presence. I've even seen Downy Woodpeckers eat out of people's hands. Pileated Woodpeckers, however, seem to fly away at the slightest detection of movement. I find this surprising as they are such a large bird. My natural instinct is to assume that larger birds need not be flighty as their size offers some protection in terms of predators. It could be though that larger animals present a larger more easily seen target. Little birds can blend in so well and hide that perhaps they need not be as flighty.
I decided to do a search of the literature and see if I could find anything. The first study I came across was this one titled, Does intruder group size and Orientation affect bird flight initiation distance in birds? (links to pdf) The answer is Yes. This study was on the size of the predator though so it doesn't answer my question.
This research suggest that at least in fish, the larger the animal the larger the Flight Initiation Distance. That's the technical term for how close you can get to an animal before it get's the heck out of Dodge. While I couldn't find anything on Pileated Woodpeckers I did find this interesting paper about downy woodpeckers. Vigilance and foraging substrate: anti-predatory considerations in a non-standard environment. This paper talks about the size of trees they use and behavior. It talks about how woodpeckers will continually peek around a tree to keep an eye on their surroundings. Pileated Woodpeckers do this in a seriously overly dramatic paranoid fashion.
The last study I found was Developing an evolutionary ecology of fear: how life history and natural history traits affect disturbance tolerance in birds. This one is great. I just had to include the entire abstract below.
When approached by humans, virtually all species flee, but we lack an understanding of the factors that influence flight response among species. Understanding this variation may allow us to understand how ‘fear’ structures communities, as well as to predict which species are likely to coexist with humans. I used flight initiation distance (FID) as a comparative metric of wariness and examined the relative importance of life history and natural history traits in explaining variation in FID in 150 species of birds. In a series of comparative analyses, I used independent contrasts to control for phylogenetic similarity and regressed continuous life history traits against flight initiation distance. Body size had a large and significant effect in explaining variation in flightiness: larger species initiated flight at greater distances than smaller species. After controlling for variation explained by body size, there was a nonsignificant positive relation between the age of first reproduction and FID. There were no relations between FID and clutch size, number of days spent feeding young, longevity, or habitat density. I used concentrated changes tests to look for evidence of coevolution between flightiness and dichotomous traits. Flightiness evolved multiple times and some clades were flightier than others. Flightiness was more likely to evolve in omnivorous/carnivorous species and in cooperatively breeding species. These results suggest that body size and age of first reproduction are important in explaining variation in disturbance tolerance in birds, and that species that capture live prey and those that are highly social are relatively wary. The results suggest a novel mechanism of how anthropogenic disturbance may contribute to extinction.
Did you catch the key sentence there? "Body size had a large and significant effect in explaining variation in flightiness: larger species initiated flight at greater distances than smaller species." Great, so the reason Pileated Woodpeckers are flightier than other woodpeckers is that they are bigger. Now then, why! Why is there a correlation between body size in birds and flightiness. Also why is it the exact opposite of what we see in fish?
~Kirk
