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The Daily Bucket is a place where we post and exchange our observations about what is happening in the natural world in our neighborhood. Each note about the bugs, buds, and birds around us is a record that we can refer to in the future as we try to understand the patterns of nature that are quietly unwinding around us.
The activity around the feeders has been very high during the past week. Our weather turned more seasonal and wintry here in Iowa. A blizzard enveloped the entire state. Temperatures have been in the single digits each night and in the teens for highs. The birds are more challenged to keep their energy levels and internal temperatures high enough to survive. I am refilling the feeders more often.


We notice the smallest birds seem the most active. Little ones the size of this Fox sparrow are non-stop feeders. The activity level is less for birds with larger volume such as this Turkey. The big ones are more casual about their eating habits. It is an inverse relationship. The behavior is related to the ratio of the surface area of the bird to the volume of the bird. The bigger birds have more of their mass and volume guarded internally from the frigid temperatures near their skin. They are able to maintain their internal body temperature more easily. They retain their heat from the metabolism of the food they eat. Since heat transfers less quickly from their body volume to the surroundings, they can be more leisurely about eating. The tiny birds have very little internal volume. They lose heat quickly as it transfers through to the outside. They must eat more often to maintain their internal temperature.

Here is an illustration of the effect of surface area and volume. It uses cubes 1 meter on a side. It works for cubes of any size. All that matters is the ratio in the end. You can try it yourself with sugar cubes. Each cube face is a square meter. There are six exposed on the single cube. Each small cube is one cubic meter. The ratio is 6:1.

The middle set has a lot of faces that aren't exposed. Notice how the ratio of surface area to volume has decreased by half to 3:1. The third set on the right has a ratio of even less at 2:1. Scale this up to 10x10x10. You have a surface area of 600 and a volume of 1000 for a ratio of 0.6:1. So, the benefit to the larger animals is the reduced surface area exposure compared to their volume where their heat energy is localized. They lose less heat proportionately from their core.




What have you been noticing in your backyard lately? Has the winter impacted much of the activity? Do you expect any big changes in the coming days or weeks? Let us know what is going on.




Originally posted to Backyard Science on Thu Dec 27, 2012 at 08:10 AM PST.

Also republished by Community Spotlight.

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