Shifting bison herd dynamics

 Over the past month or so I've been noticing a few changes in the bison herd.  Our big bull has largely separated himself from the herd and now spends much of his time sitting or standing majestically on hilltops.  He comes and goes when he pleases without waiting for a herd consensus.  The bull has always been more independent than the others, but this almost complete separation from the herd is something new. 
The females exploring the site of a solar powered water well I'm installing.
 If we count the months from March, when the bull was very aggressive towards me and attentive to the females, to now it will be around eight months.  The bison gestation period is around 9 and a half months, so it's possible that we will start seeing babies next month.  I really don't know what to look for to tell if they are pregnant.  Jess had hoped the thermal imaging device might enable us to see some sort of evidence of bison pregnancy, but bison hair is so insulating that there's very little variation in their heat emissions.

It is possible that the bull's separation from the herd is in anticipation of calving.  Perhaps they've overtly compelled him to move away or there's some kind of  chemical communication.  In addition to a change in bull behavior, I have observed multiple instances of increased aggression between the females.  Mostly this appears to involve persistent shoving and some chasing.  No one bison appears to be the focus of aggression, though.  Rather, one female will seem to suddenly decide to be a jerk to everyone else for a while. All of this could just be miscellaneous facts unrelated to bison pregnancy, but who knows. 

The two young bulls now (left) and last spring (right).
 On another note, the two bull calves we brought back from Texas last year have really grown.  They still stick close to the herd and are readily bullied by the females, but they are starting to stand their ground more often.  Today I noticed bull No. 29 chasing and mounting bull No. 28.  I interpret that as an attempt to assert dominance rather than an actual attempt to mate. 

Finally, No. 8, who suffered a case of pinkeye in her left eye this past summer, has mostly recovered now.

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