Reptile Forum, Reptile Classifieds - CaptiveBred

[Sam Sweet]

At the risk of getting run out of town I am starting another incubation thread, because I want to make a point that differs from the general discussion below, and is not something that I have seen addressed elsewhere. So far, I have neither hatched nor lost monitor eggs myself, and I am not claiming that these ideas identify the problem, or that solving them is a recipe for success.

There are major differences between conditions in incubators vs. those in natural nests. The most basic one is simply that good incubators hold constant those things that vary in nature, while creating variation in what nature holds constant. In almost all situations in nature (except perhaps within termite nests), monitor eggs are going to experience daily and longer-term variation in temperature, and irregular variation in humidity and substrate moisture. This is a no-brainer, yet most wild clutches hatch. Against this, we reckon best those incubators that allow the least possible variation in temperature and humidity, and we try to hold substrate moisture nearly constant. This is done for reptile incubators by creating a still-air, closed system quite different from the forced-air, open system incubators used for birds. Reptile and bird eggs are quite different, in part because the latter need to be turned, have to lose by evaporation ca. 15% of their starting weight to hatch (vs. needing to gain ca. 50% in weight by water uptake), and have higher gas exchange rates.

It’s the water uptake issue that defines the need for closed systems for reptile incubators, and I suggest that this may be creating a problem for monitor eggs specifically. Good respiratory data exist for Komodo eggs (Birchard et al., 1995, Physiological Zoology 65: 622-633) showing that oxygen consumption follows a sigmoid curve over time, reaching (and holding) a maximum value at about 80% of incubation time. A 175 g Komodo egg uses 151 ml O2/day at maximum uptake, which is all of the oxygen in about 750 ml of air. In reality it could not extract all the oxygen, and would need access to 2-3 liters of air to function normally. (You can calculate maximum O2 needs for other monitor eggs via an allometric regression – approximate values per egg [at 29 C] are: 10 g, 16 ml; 20 g, 27 ml: 30 g, 37.5 ml; 40 g, 47 ml; 50 g, 57 ml O2/day.) At the same time, the egg produces ca. 151 ml CO2/day, and this cannot accumulate without seriously affecting development.

Natural nests are open systems for heat, moisture and gases – substrate porosity and the large volume of surrounding material ensures that oxygen and carbon dioxide levels in natural nests do not depart much from atmospheric values of 21 and 0.035%, respectively. However, an egg box (and an incubator) is a closed system nearly all of the time, and we can expect oxygen levels to decline and carbon dioxide levels to increase in the intervals between opening the incubator and egg boxes.

Monitor eggs are relatively large, and tend to be crowded in incubators compared to those of other lizard species. In this sense they are kept like snake eggs, but a significant difference here is that oxygen consumption rates of snake eggs increase steadily until hatching, whereas monitors reach and hold a peak rate for the last 20% of incubation. The fact that monitor eggs tend to fail at about this last quarter-last fifth stage does suggest that some aspect of gas exchange could be involved. Whether it is gas exchange alone or in combination with water balance is simply unknown. Anyone here can do their sums with the size and number of eggs they keep in boxes and incubators, to see if either O2 depletion or CO2 buildup could be problematic.

There are also some general problems with ‘applied knowledge’ regarding water balance, which I can address separately if anyone is interested.

[master pt]

interesting post.
_________________
Good luck

[Mike]

Thanks for sharing Sam!
/Mike

[Sean]

Regarding incubation I had set up the eggs side by side, I think there was about 8 in the clutch some hatched at around 6 months and some went on to hatch at 11 & 12 months. Until it had happened to me I not heard of this delayed reaction before of such a long time spell.

Also I was talking a breeder in Germany regarding is panoptes panoptes and his adults are 30 years old and he still as clutch in the incubator. He only puts them together for one breeding in the year but they are still going strong, I was surprized to how old they were let alone he's still getting the same clutch sizes of fertile eggs and offspring.


2 pics of different clutches in the incubator. I use a breathable poly box in side is a large tuperware box with holes punched in the top to allow air circulation. The incubator is heated with cable from above the eggs.

I have another incubator which the cable heats the eggs from below but I have found no difference whether the heat source comes from above or below.

[Sean]

The incubators at Rotterdam Zoo.

[Sean]

Forgot mention I use 1:2 water to perlite ratio, I noticed in the other thread that people were using 1:1. I also put a small bowl of water in the poly box not in the eggs box itself.

[shay_]

one of the better topics. i think these couple threads can benefit lots of us keepers

nice pics Sean. are those v.p.panoptes? i love those little guys. cheers

[Sean]

Yes they are panoptes panoptes.

[crocdoc]

[Sean]