Renee,
With regard to live-bearing species, I don’t know of very many occurrences where large boas have been bred in successive years, and not one instance for a green anaconda. As you stated, the energy expenditure and corresponding weight loss from the developing young is just too great to be replenished before the next years breeding cycle begins. However, smaller boa species and smaller specimens of larger species have produced in consecutive years because they can more quickly gain back their weight on a captive feeding regime. Both of the green anacondas that successfully reproduced for us were in the 13 foot, 90 pound range and each had lost between 30 and 40 percent of their body weight at the time the young were born. Both females had good body weight for their size, but they were not overly heavy when the breeding began. They typically don’t feed during breeding and not for the latter 5 months or so of the gestation period. This gives them only 3 or 4 months to gain back their weight before the beginning of the next breeding season. Even though they would probably not have ovulated, I would never attempt to breed them in two consecutive years. It is not uncommon for underweight female boids to fail to produce egg follicles to avoid becoming gravid, and risking possible death or loss of underdeveloped young. This would be poor reproductive strategy and it makes sense that the wild anacondas you referred to, would ovulate on 2 to 3 year cycles considering the availability of food in their natural habitat.
Large captive pythons, being egg layers, are a different matter. They regularly reproduce in 2 or 3 consecutive years in captivity because the eggs can be pulled and incubated artificially. This will free the female from having to brood the eggs, either passively or actively, for the next 2 to 3 months, allowing them these extra months to replenish their energy reserves as compared to the live-bearing species. This is especially true with actively brooding species. When allowed to reproduce as they would in the wild, the outcome reflects that seen with the large boas. When regularly breeding burmese pythons in the 80’s and early 90’s, I used maternal incubation 95% of the time. These females were reproducing naturally, and like their large boa counterparts, they showed the same large scale weight losses seen with our anacondas. It is a major energy drain for a large burmese to maintain a consistent egg mass temperature for 56 days, with the first 7 weeks being maintained at a constant 92 F. They do put their weight back on fairly quickly, but I never did try to breed them in consecutive years as I felt the stress on them was not warranted. Sorry for the long response, but I find it an interesting topic.
Kelly
