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RE: Rubber boa's Richard?

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Posted by: RichardFHoyer at Sun Oct 9 22:26:25 2005  [ Report Abuse ] [ Email Message ] [ Show All Posts by RichardFHoyer ]  

CE Smith,
A number of factors contribute to what age and at what length specimens of the Rubber Boa reach sexual maturity. Not certain that you are aware that there are at least two reasonably distinct size morphs of Charina bottae. The dwarf form occurs in much of S. Calif. from the S. Kern Plateau in southern Tulare County and northern Kern County in the west and Greenhorn Mts. on south. To the best of my knowledge, the large morph of the species occurs elsewhere in the species distribution in North America.

In both the large and dwarf forms, the smallest, average, and longest lengths attained of time or age at which specimens become mature in the wild probably is probably the same. The minimum amount of time in the wild is probably about 4 1/2 years (perhaps 3 1/2) for males and two years longer for females. The average age is more likely to be around 5 1/2 - 6 1/2 years for males and two years longer for females. A local NW Oregon juvenile female I recaptured a good number of times took 13 years before she produced her first litter.

The process can be advanced somewhat for captive specimens if you maintain them at active season temperatures and can coax them to take prey all year around. In such optimum situations, it would be my best guess that males may reach maturity in about 2 1/2 to 2 3/4 year then be able to breed the following spring. Again, females would generally take 1 - 2 years longer to reach maturity. I did this once but am too lazy to try and locate my records so the above information is just off the top of my head.

The length at which sexual maturity is attained differs between regional populations and between the sexes as well. For the dwarf form, I once thought that the minimum size that a dwarf form male would reach maturity was around 13 1/2 to 13 3/4". Two dwarf males of 13 7/8 inches, one from the San Bernardino Mt. and one from the southern Kern Plateau in Tulare county, exhibited courtship behavior and coupled with females indicating they were mature. However, a dwarf form subadult male from the S. Kern Plateau, capture in July, 2003 at 13 1/4 inches, this past spring exhibited courtship behavior and was just 13 3/8 inches.

From the SRB study published by myself and Dr. Glenn Stewart, we theorized that the lower limits of length that a dwarf form female might become mature would be about 16 3/4 to 17 inches. The smallest dwarf form female I have found to be gravid and produce a litter was a 17 3/4 or 17 7/8 inch female from the Tehachapi Mts. It is more likely that dwarf form males become sexually mature around 14 1/2 to 15 inches and dwarf form females become sexually mature at around 18 inches. The boa population in the southern Greenhorn Mts. due east of Bakersfield and just south of Alta Sierra in Kern County appears to be a dwarf population. I captured a 16 1/4 inch subadult female in that region in May of 2003. She fed reasonably well that season and was 16 7/8 inches by early Oct., 2003, She continues to feed well in 2004 and appeared to reach sexual maturity by the end of the active season last year at 18 5/8 inches. She mated this spring and produced her first litter this year. It should be considered that in the wild, she would not have had the same opportunity of prey available or frequency of meals as she had in captivity. Thus, she may have not reached maturity until 1 - 4 years later and likely would have been considerable shorter in length when she produced her first litter.

Without actually organizing data and producing some calculations, don't take any of the above as the gospel but just educated guesses at this point.

There probably is considerably more variation amongst populations of the large form of Rubber Boa. With more assurance, information on the local population at low elevation here in northwestern Oregon, males reach sexual maturity at around 18 inches and females at 22 inches. Out of hundreds of local gravid females I have recorded, only three that produced litter and were slightly below 22 inches. At my study sites in the mts. of SW Oregon at 5000 ft. and above and my arid 4400 to 4500 ft. study site in E. Oregon, the lengths at which males and females of the large morph become mature is probably around 1 inch lower than for the local population. Not having gathered information on large enough samples from other regions, I can only make educated guesses but the above should give you some idea.

As far as feeding is concerned, there is a very wide range in behavior in that regard. I have had some Rubber Boas that consumed everything thrown their way while others that have refuse to feed for over a year. As a general rule, the species will more readily take nestling small mammals of our native species over the lab mouse. But I have had several boas that have never hesitated taking nestling lab mice.

I maintain a lab colony of our native Deer Mouse (Peromyscus maniculatus) for he purpose of trying to get reluctant feeder going and also collect nestling small mammals (voles, mice, shrews, shrew moles) locally when ever I encounter them and freeze them for later use. Lizard eggs are a staple for some populations of the species and they will also take small lizards of various species, sometimes small garter snakes and small snake eggs. But their primary diet in most regions appears to be nestling small mammals.

A gentleman in S. Calif. informed me that one or more of his boas also readily takes rat pups. I have never tried them. In a few feeding trials this summer, all of 11 W. Fence Lizard eggs were consumed, none of the Ringneck Snake eggs were taken but a number of Sharp-tailed Snake eggs were eaten by some of the boas I am maintaining. I have never tried garter snakes but have two friends who have had boas take small garter snakes. There is a published note to that effect as well.

Richard F. Hoyer


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