Why turning matters
The reason birds turn or move eggs during incubation has long been observed but only recently understood -and still probably not fully. D.C.Deeming in his book ‘Nests, Birds and Incubators’ explains the physiological effects of not adequately turning eggs: in particular, retarded embryonic development, malpositioned embryos and increased early and late stage mortality. Turning is much more important at certain stages of incubation, particularly the first week with precocial species (hens, ducks, game birds, etc.). Even more energetic turning is probably necessary for altricial species; parrots, falcons and many wild birds, where proper vein development appears to be inhibited by insufficiently frequent or inadequate angled turns. (See Practical Incubation by Rob Harvey.)

Check back with Nature
All too often designers of small incubators have pursued assumptions about what eggs ‘need’ from the long established practices of commercial hatcheries. But what works for chickens does not necessarily work well for non-domesticated birds. The natural process has to be the starting point. Deeming’s ‘Birds Nests and Incubators’ commences with an incomparable review of scientific studies of natural incubation behavior of a wide range of wild birds.

Fascinating insight into turning of Parrot eggs comes from the infra red monitoring of pairs of various species nesting in boxes. Analysis of over five thousand hours of video by Carla Freed (Reproductive Behaviors in the Nestbox-How Parrots Parent, AFA 2001) concludes that some degree of turning or movement of eggs is often very frequent, up to twelve times per hour, and that turns are very random. She also observed that eggs could tolerate surprisingly rough treatment, often inflicted by males.

Further observation from leading Australian parrot breeder Peter Gowland www.priam.com.au indicates that as eggs loose water and the air sack expands asymmetrically, the egg tends to lie predominantly on one side with the air sack uppermost. Thus at later stages, say after half way, natural turning tends to be movement away from and back to the position favored by the center of gravity. Excessive turning late in incubation outside this range may be a cause of malpositioned or inverted embryos, and in any event ceases to have the importance of more energetic turning in early stages.

Common egg turning mechanisms:
Various automatic methods have been adopted in incubators to provide automatic egg turning and most work satisfactorily with some intervention. Here are the most usual examples with comment:

Tilting trays
Virtually all commercial incubators are provided with plastic egg trays which hold the egg essentially vertical, small end down. The tray is then tilted through an angle of about 40°either side of horizontal (an 80° angle) at predetermined intervals, perhaps every hour. This method works well with poultry for which it was developed, and is very efficient to operate on a commercial scale. However, it is very different from the natural process adopted by birds, which is more random with eggs near horizontal. Fine for poultry, because of their long history of domestic evolution but not good for wild or less domesticated birds. Hand turning through a larger angle is not possible; twisting an egg in its tray merely anticipates the next automatic turn.

The Brinsea Octagon range of incubators uses essentially the same principal though the cabinet moves with the trays of eggs. The eggs are often set lying down instead of vertical, which is closer to most natural environments. Periodic hand turns (24 hours) through a large angle, say 180° over the small end is easily done and highly recommended with altricial species in early stages. If egg dividers are set a little apart, a greater angle of turn can be achieved that the 90° turn of the cabinet by allowing eggs to roll slightly.

Moving floor
In a number of small incubators where there is no need for multiple layers of eggs, the eggs lie on a horizontal floor or conveyor which moves from side to side. Eggs are restrained from much lateral movement by fixed dividers so that the eggs roll, instead. This kind of system works well with eggs which are reasonably symmetrical, end for end, as duck eggs often are for example. Eggs which are significantly pointed tend to roll in an ark as a cone would, as a result they progress in the direction the small end points and can end up bunched together. This wouldn’t particularly matter except that the small end can easily end up high, riding over the next egg, and this may be a problem in promoting wrong end hatching.

Careful daily monitoring and repositioning of eggs helps to prevent such problems. The last stages of incubation are particularly important in orientating the embryo correctly.

Rollers
Rollers are usually an extension to the moving floor idea, sometimes being rotated by a moving floor. Eggs sit on rollers which in turn sit on the moving floor. Ribs on rollers help reduce the tendency of eggs to ‘walk’ along the roller length. A novel adaptation of the roller system used in the new Brinsea Contaq X8 provides alternative rollers for widely different sized eggs, allowing them to be turned through similar angles with the same program settings. Some degree of random positioning is probably desirable and certainly reflects the natural process. Brinsea Contaq incubators can be programmed to give random intervals between turns down to 5 minutes, random angles and even random directions.

Troughs or Channels
Semicircular or similar shaped channels are offered with some incubators, for quail in the Brinsea Polyhatch, for example. This can be a good method of controlling turning of small eggs but the turn angle is limited for altricial birds unless augmented by hand turning. It may be an excellent solution though, for late stage altricial eggs, where limiting turning to a gentle ‘rocking’ is probably ideal. An extension of this concept is to enclose eggs in some kind of cage so that larger angles of turn are possible. This provides very tight management with a high risk of ‘mechanical imprinting’. As always – check back with Nature!

Perfection?
The ideal for altricial species in early stages seems to be frequent, random movements, some through large angles (180°+). This should progress later in incubation to movements, still fairly frequent, but allowing the egg to return to its natural gravitational position with the air cell uppermost. Frequency for altricial species: five minutes and upwards. Precocial species certainly require less frequent turning and through smaller angles, possibly more regularly.