Bison at La Brea Tar Pits

This site tells me that bison mating season starts in July and can run through September. That's a spread of three months. They give birth therefore in Spring/early summer.We shall say then that birthing starts in April, running through to June. One month later (July) mating season starts again, and one month after that they arrive at the tar pits (in August). This means that the calves that were born in April (the eldest) will be 4 months old; the youngest calves, born in June will be only two months old.In this case, you are right - if they stayed a few months, we should expect to see 5 and 6 month olds.However, if birth happened closer to the time of their arrival things might be different. Especially if younger calves are treated differently. I can't find any particular information that would be definitive either way. However, at two months old, the calf begins to develop its horns and humps. I'm also reading that most calves are weaned by late summer. The latest calves to be weaned take seven months, but it seems a few get their earlier.Perhaps the calves we see in the pits were weaned? We'd need more information to be sure (the nature of the teeth wearing for example).Alternatively, as Lithoid has said, it could be that we are getting the information worded within error bars (that is, the ages of the calves found are 3 months plus or minus one month).That said, kudos for have a critical mind and percieving the strangeness of the numbers. We need to look at some primary literature concerning the aging of these bison, so we can establish how the museum have interpreted it for easy consumption.

Quite. The specific dates are not important, but the relative dates are. Assuming there are no other factors involved would seem to suggest Christian was right - however as you say, there are likely other factors not discussed in the brief text presented.

I covered a couple of possibilities at the bottom of my Message 8.

Well it seems we have either a contradiction of sources (the ones I looked at suggested differently with 7 months as a maximum, and some reason to believe it might be shorter), or different definitions of nursing and weaning. As I said, we'd need more information on the whole thing. It could be that the age span of bison in the area included younger bison, but that the older bison are particularly vulnerable (eg they have more independence, but not the sense to fully keep out danger). This might the age, for example, where the weaning process begins - so the young 'ens start exploring for food.Unfortunately, without decent levels of information, I'm unwilling to to provide any solid conclusions. I think the point is that if they age a bison at 4 months old, the error on it is 1 month either way, so the bison could be 5 months old or three months old. At the other end they might age it at 2 months, but the error bars give us between 1 and 3 months. At this time, they've not found anything that dates to 5 months (plus or minus a month).As such the potential age of the bison is between 1 to 5 month. That accounts for staying in the area for a while and a gap between calves. It might be that they have averaged the tested age as being 3 months, and applied the error bars to that for 2-4 months.Once again, we'd need to know the primary information in order to discern how the museum has simplified it for the public.