In Sync

As the weather warms, the zoo is full of changes as animals return to their exhibits.  Obviously there are a lot of tropical animals that are kept indoors in the winter which can now go back to their outdoor spaces.  Even among the northern, more cold-tolerant animals, however, there are some major exhibit changes.  While some species, such as bison and snow leopard, are just as active throughout the year, others - animals which may have spent the winter denned up and dormant, as they would in the wild - start to wake up as well.  Brown and black bears, for example, gradually wake up, ready to feed and shake off the dust of their winter dens.

Something I find fascinating about North American mammals is that - for the species with large ranges, extending from far in the north to far in the south - there are major variations in how animals behave throughout the year.  Which makes sense, when you think about - "winter" for a black bear in Canada is very different than "winter" for a black bear in southern Florida, requiring very different.  A bear in one habitat has months of very little food availability and has to gorge in preparation.  A bear in the other has fairly stable conditions year-round.  Their anatomy may be different too, especially in terms of size; Bergmann's Rule states that, in a species with a large geographic range, individuals closer to the poles are more likely to be larger and heavier-bodied to conserve heat than their warmer-weather cousins (applies to the Old World as well as the New - Amur tigers of Siberia are bigger and shaggier than tropical Sumatran tigers).

What I had not counted on was the fact that animals of the same species but from different parts latitudes might have trouble breeding.

Breeding is much more seasonal in northern animals, as you want your babies to be born at a time of year that maximizes their likelihood of survival  What that time of year will be varies based on your location in the range.  So, if you take a male river otter from Louisiana and a female from British Columbia and put them in a zoo exhibit to breed (many North American river otters in zoos are orphans or other non-releasable animals that are placed where there is room for them, which may end up being far from their birth site), their reproductive clocks might never synch up.  Even if you see them physically breeding, it is less-likely that a pregnancy will result.  You'd have better luck pairing up together two otters from more southern locations, and two otters from more northerly ones. 

I'm continually amazed at the complexity of breeding so many species; there always seem to be new details we're learning about to explain success and failure.  The more we learn, however, the more successful we can be in the future.