Eating Like a Bird

Faithful readers know that I am a sucker for data. It's only natural that I would eventually start crunching the numbers on seed consumption here at Cary BirdCam. So here's a go at answering the question, what does it mean to "eat like a bird?"

I refilled two tube feeders this morning with a total of 11.5 ounces of black oil sunflower seed. That equates to 9,200 seeds (I counted the number of seeds in a half ounce: ~200.) Thus, I induce the following, for a none-too-cold October day:
(1) My best sense of things from BirdCam photographic evidence is that something like sixteen birds used these feeders yesterday. (10 house finches, 2 Carolina Chickadees, 2 Tufted Titmice, a Brown Headed Nuthatch, and an American Goldfinch). If that is the case, then the average bird consumed 575 seeds. This is a high end estimate because of wastage. That's 0.7 ounces of raw seed and 0.4 ounces if we substract the weight of seed hulls.
(2) The weight of one House Finch is approximately 0.7 ounces, so we can conclude that the average bird is eating half its weight in sunflower seeds every day. I presume they eat other foods (at the very least they also eat safflower seed at my feeders!), and the finches are the dominant consumers at the tube feeders, hence it is no stretch to infer a food consumption approaching full body weight.
(3) For you nutritionists out there, that level of consumption (0.4 ounces) represents approximately 1,000 calories (I found a per pound calorie estimate for sunflower seed here.) I remember seeing someplace that birds are assumed to need 2,000 calories a day, so we can make an educated guess that my finches and their friends are not doing it on sunflower seed alone.
(4) Watching birds eat, I figure that the average House Finch put the smack to one seed every three seconds. To eat 575 seeds would only take it 29 minutes of work. Happily these birds are not at the feeders all day!
(5) A fifty pound bag of black oil sunflower seed should provide enough food for sixteen birds for 70 days. I won't do that well because the squirrels are also eating sunflower seed. So let's say I run through fifty pounds in no more than a month.

These are not flawless data, and more rigorous methods of counting birds would be necessary to derive ironclad findings, but I think we have enough here to put seed consumption in perspective. No one would want to truly eat like a bird! Tomorrow: what did squirrels eat?