Air Temperature: the air temperature within the incubator. Even with the most expensive incubator, air temperatures will consistently fluctuate (vary). The temperature will rise when the heating element comes on and then it will drop when the element goes off – frequently as much as a full degree (even more so with cheaper incubators). The more insulation and effective the air flow, the less the air temperature will vary. However, these variations only have a minimum impact on the developing embryo.

Realized Temperature: the temperature physically experienced by the embryo. The developing chick is insulated from the air temperature by its cuticle (bloom), shell, inner and outer membranes, and the albumen (egg white). Just as it takes time to boil a pot of water or freeze water in an ice tray, it takes time for the embryo to physically experience a rise or fall in air temperature. How quickly an egg’s temperature changes depends on factors such as humidity, air speed, and egg size.

Broody Hen Example: When a broody hen sits on a clutch of eggs, she is using conduction (touch) to transfer heat to the eggs with only one side being warmed at a time. A hen’s internal body temperature runs between 105-107°F and we can assume that the temperature of heated side of the egg is well above the 99.5°F that we commonly use in artificial incubation. That broody hen will turn her eggs up to 50 times a day so that no one side is heated/cooled for an extended period of time. From her example, we can learn that temperature variation is of less importance than the AVERAGE temperature physically experienced by the developing embryo – the “realized” temperature.

The Problem with Digital Thermometers: When I started back incubating a few years ago, I spent quite a bit of money on thermometers. Unfortunately, those expensive thermometers were useless in an incubation environment. In fact, most were detrimental (damaging) especially the most responsive ones like the renowned Brinsea Spot Check. You see, accurate and responsive digital thermometers react to even the slightest change in air temperature. When the heating element comes on, the reading rises. When the heating element cuts off, the reading drops. These variations caused me to fiddle with my thermostat… and fiddling with the thermostat with eggs in the incubator can cause all sorts of problems.

The Solution: Expensive digital thermometers do not work well for me. They accurately and precisely measure the “air” temperature but they aren’t very helpful in measuring the “realized” temperature. What I needed was a thermometer that reacted to changes in air temperature more slowly… one that measured the average air temperature… one that better represented the “realized” temperature. My solution was to return to the inexpensive, calibrated, red spirit filled thermometer (old faithful) I had first purchased at Tractor Supply shortly after my wife gave me a Little Giant incubator for Christmas. That thermometer responds to changes in air temperature but more slowly… more in line with what the embryo actually experiences. Since I returned to using old faithful, my babies hatch when they are they are scheduled – and that is the true measure of a good thermometer.

Lesson Learned: Newer and more expensive does not mean better. Since my Little Giant days, I’ve moved on to bigger and more expensive incubators; however, my good and faithful glass thermometer remains the cornerstone of my temperature monitoring. At this very moment, she sits in my hatcher constantly keeping vigilance over my hatching babies.