Artificial incubation of angulate / angulated / bowsprit tortoise (Chersina angulata) eggs, especially outside their native land, has proven to be quite challenging. Many angulate keepers share similar stories: a great number of eggs will not develop at all, a few will start developing and then stop, and even fewer will actually hatch.
Although I’ve been fortunate to hatch a small number of baby angulates, I have not yet found the best method for incubating their eggs either. I've used a few different incubators, various substrates, different temperatures, and higher or lower humidity levels. I've also incubated eggs with and without cooling (diapause) and with and without night temperature drop. I’ve left some eggs in the ground as well. No modification seemed to improve the hatching rate.
After cracking the egg open, this angulate baby decided to turn around and stay a bit longer inside the shell. He crawled out of the egg the following day.
Incubation techniques for angulate eggs vary among breeders. Some keepers cool the eggs before incubation while others don't. Same for night time temperature drop, some utilize it and some don't.
Below are some examples of incubation temperatures and humidity levels breeders have used. For full details, please read the original publications.
1.) Bauer, Thomas (Turtles, Proceedings: International Turtle & Tortoise Symposium Vienna 2002, 2006)
Egg box is filled with slightly damp, sterilized soil. Eggs are placed in shallow depressions, but not buried. Eggs are incubated at 27-30 °C (80.6-86 °F) with 85% humidity. Incubation lasts 110-125 days.
2.) Caroldi, Luke (TartaClubItalia.it, 8/2011)
Reported incubation temperature for angulates was 30 °C (86 °F).
3.) Facebook (2014, 2017)
One angulate keeper in South Africa incubates eggs at 28 °C (82.4 °F) or 29/30 °C (84.2/86 °F) with 60% humidity on vermiculite mixed with water 50/50. (2014) ... Another keeper in South Africa incubates eggs at 28-32 °C (82.4-89.6 °F) with minimum of 60% humidity. Eggs hatch in 112-140 days. (2017)
4.) Fleck, Jürgen & Susanne (Elaphe, 3/2001)
Eggs are incubated on vermiculite at 30 °C (86 °F) with 80-90% humidity. Incubation lasts 95-127 days.
5.) Highfield, A.C. (Practical Encyclopedia of Keeping and Breeding Tortoises and Freshwater Turtles, 1996)
Eggs are incubated at 30 °C (86 °F) with 60-65% humidity. Incubation lasts 90-100 days.
6.) Jasser-Häger, Irmtraud & Philippen, Hans-Dieter (Testudo magazine, Schildkröten Interessengemeinschaft Schweiz, SIGS.ch, 6/2003)
Eggs are incubated at 28-31 °C (82.4-87.8 °F) on dry gravel (Kies) with about 80% humidity. Incubation lasts 90-120 days.
7.) Junek, Milos(Euzelva.cz)
Eggs are incubated at 30.5-31 °C (86.9-87.8 °F) with 95-97% humidity in a water incubator. Reported incubation lasted 101 days.
8.) Koehler, Gunther (Incubation of reptile eggs, 2004)
Eggs are incubated at 27-30 °C (80.6-86 °F). Incubation lasts 95-127 days.
9.) Steehouder, Trudy (Lacerta 52/5)
Three females laid several eggs, but only one hatched. It was incubated at 28 °C (82.4 °F) for 117 days.
10.) Sterantino, Dan (Chersina Angulata Working Group, Trevor Zoo, 4/2019)
Eggs are buried 1/2” deep in a 3 to 1 mixture of top soil and sphagnum peat moss within a small rubbermaid container with a loose fitting top. The soil/peat mixture is moistened so that a hygrometer sitting on the substrate reads above 95% RH the entire length of incubation. Incubation temperature is 85 °F (29.4 °C) during the day and drops to 70 °F (21.1 °C) over night. Incubation takes 130 to 135 days.
11.) Turtle Survival Alliance (TSA journal, 8/2007)
Turtle Conservancy's Behler Chelonian Center (TC-BCC) hatched their first angulate tortoise in 2007. This egg was incubated at 30 °C (86 °F) in a closed plastic container using vermiculite, mixed with water in a 5:1 ratio, as the substrate. Incubation lasted 96 days.
12.) Wlach, Sven (Schildkröten im Fokus, 2/2008)
Eggs are incubated at 31 °C (87.8 °F) for 20 hours a day and at 25 °C (77 °F) or below for the rest of the day. Humidity is kept above 50%. Incubation lasts about 120 days.
Freshly hatched angulate baby.