Size Really does Matter

Autumn is a magical time, full of the fresh scent of fallen leaves, crisp, blue skies and the plaintive grunts of horny ungulates.

Yes, folks, it’s mating season in the boreal forest, known in the deer world as the rut. As the days get shorter, hormones start running rampant. Lean, muscular bodies have reached peak condition after a summer’s diet of green, leafy vegetation. Pheromones are being produced in vast quantities to be splashed onto every available surface. But, for deer and moose, it’s really all about the antlers, which have now been scrubbed clean of their protective velvet layer to gleam in the warm autumn light like a warriors sword.

Unlike what us human females like to tell our potential mates, size, in cervids, truly does matter. It’s all about who has the biggest rack.  Think about it, ladies, which would you be most attracted to: the young, scrawny male with little knobs that just barely make it past his ears, or the magnificent bull with antlers stretching over a meter from tip to tip? In female ungulates, the choice is ingrained: bigger is better because she’s not just seeing an impressive display, she’s seeing good genes.

Those antlers are what behaviourists call ‘honest signals’. Only males healthy enough to carry around all that weight can display them. Take moose (Alces alces), for example. Antlers of a large bull can span up to 5 ft (1.5 m) across and weigh 60 – 85 lbs (27 – 39 kg).  Male moose spend 25% of their energy in the summer just growing them, using more resources than females put into gestating young.  Antlers grow fast, starting to form in mid-summer and reaching full size by September. In fact, moose antler is the fastest growing bone tissue known. Growing it is one thing; then they have to carry them around for another few months.

It’s for that reason, that antlers are such a reliable signal of male health and why they are so attractive to females. If the male is strong and healthy enough to carry around 70 lbs on his head just to look good, he should father some healthy calves.

Another theory explaining why females choose males with larger antlers and other ornaments is known as the ‘sexy sons hypothesis’. The idea is that females choose males with the largest antlers, longest tail or brightest colours because they figure they will father sons who are equally attractive, ensuring they will pass on their genes to future generations. Either way you look at it, it has resulted in some pretty amazing looking animals.

These racks aren’t only for show. While in most cases, it can easy to determine a winner when two competing males cross paths, sometimes the match-up is too close to call on sight alone. In those situations, a fight usually breaks out. Like two hockey players, they launch at each other and lock heads, pushing and grunting until one eventually gives up. Although death is rare, fights can be dangerous. You can get cut, or gouged or, like the one pair of bull elk I watched, one can push the other into oncoming traffic.

For this reason, male ungulates spend a lot of time sizing each other up before engaging in any combat and they’ve evolved some more sophisticated ways to do that besides standing around comparing sizes. Those pheromones they splash about contain a lot of information on each individual’s  health and status. Many species, like white-tailed deer (Odocoileus virginianus), create pheromone markers all over their territory by scraping bark of small trees and rubbing scent glands at the base of their antlers onto the exposed wood, leaving their calling card. This allows other males entering the territory to decide if its worth taking this guy on without having to see him.

As the days grow shorter still, the furor eventually comes to an end. The females are with calf and the hormone levels in males peter out, leaving them exhausted, but hopefully satisfied. Having served their purpose, the antlers drop off, likely affording a great deal of relief, but it’s only a few short months before the next rack starts growing and the cycle starts again.

7 thoughts on “Size Really does Matter

  1. You have a wonderful way of marrying a lightness of touch to natural history and biology , Heather. From the comic to the serious, these posts unfold with an ease that enables me to absorb the information readily, while bringing to the surface further questions, connections and ideas. To widen the circle of my thinking. Thank you for these journeys which are both beautiful and educational.

    • Thanks, Julian. I’m glad my slightly warped sense of humour works in these posts. I’ve always tried to use a chuckle as a way to engage my audience. I find that if you can get someone to laugh, they’ll often remember why, and thus hopefully remember at least part of what you were trying to teach them. I’m happy to know it worked in this case.

  2. Well said Julian! And, speaking of thought encouraged… another reason for maybe Mamas to moon over those massive missives of moose masculinity? The bigger they are, the longer he’s been around (and what female wouldn’t want their offspring to inherit the survival instincts that help ensure longevity? ; ) D.

    • I think you might win for best alliteration, Deb. Your theory is also sound and plays into the overall honest signal hypothesis. If they’re healthy, they’ll live longer and be able to not only grow large antlers, but carry them around. Excellent thoughts.

  3. Lovin’ alliteration (or onomatopoeia; )
    Seriously though? While good health is obviously important, there’s actually more to it than that…
    Dad used to say that he believed the deer sat back in the woods and laughed at the hunters going in circles searching for them… Lack of respect for animals’ intelligence is Man’s(human’s) most common mistake.
    This is, I believe, what accounts for this lust for “the biggest rack”. In the case of a hunter strictly for braggadocio, but for the doe intelligence is what she seeks and long life is directly linked to intelligence.

  4. As I mentioned to Julian a while back, sometimes coming in late is a good thing. As inspiring as the lecture might be, I often enjoy the conversation in the break as much as the address. I was going to comment on your admirable flair for the instructional narrative, but Julian has already said that so very well. I won’t even try to compete with Deb’s word play or either of your wonderful humour.

    Moose are incredibly impressive animals. I had the rare pleasure of watching 2 young bulls ‘face off’ once and it is a memory I will never forget. Reading your post gives me a deeper understanding and thus respect for these wonderful critters. Thanks for that.

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