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56 Hand-Rearing Birds

control system in some incubators. They are slightly less accurate than electronic controllers. They
deteriorate over time and should be replaced annually.
Humidity may be provided by an automatic humidifier with either an evaporative pad or fine
mist, or by simple evaporation from open water reservoirs. Automatic humidifiers are usually
accurate and effective but are difficult to clean and disinfect, particularly during use. Unless
mounted into the machine, most open reservoirs are easily changed out for cleaning. If not,
using simple water pans in lieu of the humidifier built into the machine may be easier. Humidity
is controlled by increasing or decreasing the surface area of water, usually by adding or removing
pans. To ensure consistent humidity, pans should be straight‐sided, made of nonreactive mate-
rial such as stainless steel or plastic, and kept full at all times. With multiples of the same sized
pans, both changing humidity and changing pans is easily done. All humidity systems should
use distilled water or reverse‐osmosis treated water only to prevent mineral buildup and micro-
bial growth.
Turning mechanisms fall into three types: trays that are rotated, rollers on which eggs rest, and
grids (or bars) that either push eggs along a substrate or hold them over a moving substrate.
Rotating trays are usually safe as eggs do not actually move but many do not rotate through an
adequate radius of 90°. Used properly, rollers provide sufficient turning radius for most eggs,
although small eggs receive more turning and large eggs receive less. If rollers are improperly
spaced, eggs may “ride” the rollers and receive little or no turning. Eggs with a more conical shape
tend to “walk” toward one end of the rollers. Placing eggs point‐to‐point will minimize this. Grids
or bars that push eggs have a greater chance of breaking eggs, but this potential varies greatly
among machine designs.
Incubators may also be used as hatchers, but these functions should be done in separate machines
to prevent contamination of incubating eggs and to accommodate changes in temperature and
humidity during the hatching process. Machines designed specifically for hatching are also avail-
able. In addition to the models listed above, Brinsea, Rcom, and A. B. Newlife make hatchers.
Spare parts, especially thermostats and fan motors, for both incubators and hatchers should be
kept on hand to quickly repair mechanical problems during incubation.
It is important to invest in high‐quality thermometers. Better mercury, mercury substitute, digi-
tal, and bi‐metal‐dial thermometers with a range bracketing that of incubation and readable incre-
ments of 0.1 °C or F should be used. All should be calibrated annually. Use of mercury has been
prohibited in many areas due to safety risks but a proprietary blue “spirit” liquid is now used as a
substitute in certified and other high‐quality thermometers. A laboratory‐grade ASTM‐certified
mercury or mercury substitute thermometer, Model 18F or 18C (VWR Scientific, Fisher Scientific,
or Cole‐Parmer), is useful for this but is not typically used directly in incubators as they are expen-
sive and fragile. Digital thermometers and thermometer/hygrometers, certified as “traceable” from
scientific supply vendors, have the advantage of being able to stay on continuously, allowing accu-
rate readings without opening the incubator door. Similar‐looking models are available from some
incubator vendors but have not performed as well and do not stay on continuously. Inexpensive
digital room thermometers and alcohol or red “spirit” thermometers are not accurate enough for
egg incubation.
Humidity in egg incubators has historically been measured using wet‐bulb thermometers, other-
wise known as sling psychrometers, but these devices are being replaced by digital hygrometers in
most applications. One end of a cotton wick is placed over the bulb of a secondary thermometer and
the other end in a small water reservoir, usually a glass tube. Often only the reading of this wet bulb
is used to record humidity, but true relative humidity is actually calculated from the differential
between the dry and wet‐bulb temperatures. The same wet‐bulb temperature will indicate different