I’ve heard from several different sources (some of them terribly unreliable) that reptiles don’t ever actually stop growing throughout their entire lives - not that they grow as rapidly as when juvenile, but just that it never actually stops. Is this true?
If it is true, what about birds? Do they continue growing as well?
(I’m asking because my budgerigar, which is now over a year old, appears still to be actively growing - not fast, but he’s measurably larger than he was a couple of months ago.
birds, no
reptiles, most of them, yes. It also means they never “get old”; there is no theoretical limit to their life span until they get somehow killed.
I know little about birds, except that there are certainly maximum sizes and identification is often linked to size, so these maximums are consistent for adult of a species.
Reptiles, I know more about and cannot agree with Sapo. My cite is my own book, Crocodile: evolution’s greatest survivor, and therefore the long list of references in the back. So I am only talking crocodilians (crocs, alligators, caimans and the gharial). Their growth rate is dependent on food and they can technically grow their entire lives, but the rate of growth diminishes greatly as they get older. So a big croc is an old croc. A small croc may also be an old croc. So technically, the OP is right, but the grown may be negligible in a big old guy.
As for there being no theoretical limit to their life span - I have never heard that one before. Despite mythical old animals of more than 100 years and mythical huge ones, the research into America’s most famous old, huge alligator, ‘Old Monsurat’ shows that he was probably only about 50 years old and about 5.6m - despite rumours of much more. Reptilians lose their teeth regularly, with them being replaced by smaller teeth which grow within the tooth cavity. With alligators, these stop regrowing at about 50 years or so (this all depends on their living conditions), and hence they can no longer feed. Crocs most certainly die natural deaths of old age, and I have no doubt the same is true for other reptiles.
The article is just about to pass into “paid subscription only” mode so be quick to check it out. Here is a quote of the relevant part with the names of the researchers if someone wants to find a better link to their work.
Thank you for that, Sapo. Fascinating article. They certainly live to extraordinary ages, but they do die at 250 years or so. The cases quoted were not run over or killed. I don’t think he literally meant indefinitely - as if - for ever and ever. I think he meant for extraordinarily long lifespans.
I don’t think that can be extrapolated to all reptiles.
Humans shrink though, after we reach our maximum size. Assuming that you need to “grow” just to maintain the same size, or that the growth may be so insignificant, it seems entirely plausible that a bird could technically be considered to still be growing, without it being very obvious, or even particularly measurable.
Indeed in the wild, where things seem to die or get eaten before they reach any kind of ripe age, it seems possible that the standard size is just a statistical effect. Of course birds aren’t indefinitely scalable (if they want to retain the power of flight) - the amount of growth I’m talking about here is maybe a 5 % increase in body size over the last six months. It might not sound as though that would be noticeable, but in the case of my pet bird, he can no longer fit through a gap that was merely a tight fit a few months ago.
This herpetologist’s MB post seems to say “no” to the notion of immortal reptiles and would explain why even turtles (granted really, really old turtles) eventually die of old age.
I really have no clue what “Hayflick limit” or “SV40 transformation” means.
The thing about budgies (and parrots) is that they live to be quite old. If your budgie continued to grow even a little bit (your 5% in six months, say), it could end up the size of a turkey.
Well… there’s the strange thing - he’s a small bird anyway; most of the birds in the aviary he came from are twice his size - which made me wonder if they’re just bigger because they’re older. It may not be that at all - it might be that they are show standard breeding stock and the offspring being sold as pets are the ‘culls’ - i.e. the ones that are never going to make good show birds.
Well, unusually for me, I did a bit of math. I reckoned that if in the first six months, your five-inch bird grew 5%, in the second six months grew 4.75%, etc., carrying the calculation forward with the growth rate steadily diminishing to zero, then after 11 years, your parakeet would be over eight inches tall. It seems unlikely to me. Parakeets have been kept as pets for a long time, and if this growth had been observed before now, we’d know about it.
My book won’t be released in the US until July next year, so I’m not doing a sell! Try Leonard Lee Rue III, "Alligators and Crocodiles’ p. 85. There are many claims of larger ones, and the actual largest is debated, it depends what degree of authenticaton you require.
It’s possible that it is just a combination of weight gain and a few more feathers, or thicker ones. I thought I had detected an increase in height too though, but this isn’t as easy to accurately measure as is weight and general size. He’s only just over a year old - I’m not even sure whether that means he’s outside the age range for normal juvenile growth.
Of course, it’s also possible that there is some kind of disorder such as an overactive gland…