So I was a skinny kid. I was a picky eater and would sometimes skip meals (I kind of wish I had that problem now, I eat everything and have to actively control my portions). It was to the point where my parents thought there was something wrong with me. They always used to use the phrase “you eat like a bird.” Which I would not know how to take because, lets be honest, how much do birds REALLY eat? Well I was doing some research for a post the other day and came across some numbers that I wanted to share about the whole “eating like a bird” thing. The results were staggering.
So I was researching to write a short post about the Mourning Dove (go check out the previous post) when I saw on the allaboutbirds.com website how much they ate. The stats showed that a Mourning Dove eats 12%-20% of its body weight and up to 71 calories per day. That took me back to my dad telling me “Jay you eat like a bird” so I had to do some more research and number crunching. So a dove is a relatively small bird, but by far not the smallest bird species. They weigh in at an average of 4 oz. (113.4 g). So if a Mourning Dove eats 15% of its body weight, it eats .6 oz (17 g) of food per day. Which to a human is like literally a handful of peanuts. That can’t be significant…right?… WRONG!! I did some comparisons. If a human weighing 150 lbs. (68 kg) eats 15% of their body weight in food they eat a staggering 22.5 lbs. (10.2 kg) of food a day (according to a nutrition website I found, humans in America eat on average 3-5 lbs (1.3-2.3 kg) a day). That is a HUGE difference, that means that a human on average eats only around 2.6% of their body weight each day. Now for the calories, these dove eat around 71 calories per day. In the light of counting calories and when a burger is like an insurmountable amount of calories, that isn’t that large… right?… WRONG again!! Lets put that into context with what we are supposed to eat. A “healthy” amount of calories for the same 150 lb (68 kg) human above is 2000 calories per day. That equals out to around 13.3 cal/lb (29.4 cal/kg) or 0.84 cal/oz (0.029 cal/g). Now we remember that this bird weighs all of 4 oz (113.4 g) and that 71 calories goes a long way. To be exact this 4 oz (113.4 g) dove eats 227.56 cal/lb (628 cal/kg) or 14.2 cal/oz (0.682 cal/g). This is also a substantially higher amount. For both amount of food and calories per body size this is about a 6-7 times larger number for birds than it is for humans. So If you are “eating like a bird” it is pretty bad and you may want to see a nutritionist because it will most likely lead to obesity. Unless of coarse its Thanksgiving, then that is pretty normal, and ironically you will probably be eating a bird.
Upon a little more research I found that these stats for the Mourning Dove is pretty low compared to some other bird species. Chickadees eat around 35% of their body weight in food per day and hummingbirds can eat somewhere upwards of 100% their body weight in nectar per day. Just don’t go around telling people they “eat like a bird” anymore because if they have seen this post, in which they will probably take offense.
I did want to briefly (to the best of my ability) give my best explanation to why this is (and how I know). I had a grad school professor that taught me Comparative Anatomy and Physiology. He hit home a lot about the subject of Fick’s Law (I’m not going to go into great detail, google it for better understanding). Fick’s Law is a measure of diffusion, or exchange rate between 2 areas through a concentration gradient. In this scenario we are talking about heat loss through skin. Fick’s Law explains that when you have a higher surface area:volume ratio you loose heat faster (because you have more surface area touching the outside world for the heat to escape through). Smaller organisms such as birds have a very high surface area:volume ratio, so they loose heat a lot faster than larger animals, ie. humans. Because birds and mammals are both homeothermic or “warm-blooded” they are required to keep their body temperatures at a high level. Since these birds loose heat faster, and because flying takes up a lot more energy than land locomotion, their metabolism is constantly running at a increased level to keep their bodies the correct temperature. To do so they need constant fuel to keep that engine running.
This is especially important during the winter months when food is scarce and temperatures are lower. Putting out birdseed is important during these months to help these birds get through the winter. With them loosing vital habitat due to development, they loose the areas that were once rich in food. Feeding these birds is one way I like to think I am helping out. And, to tell the truth, I think they are awesome to look at as well.
Jay's Nature Blog 