I’m Learnin’ to Fly

Osprey practicing flightI’m always on the lookout for wildlife, even when I’m driving 100 km/h down a highway. My sister used to always get annoyed at my penchant for pointing out hawks circling overhead or braking suddenly to check out some mergansers along the lakeshore.

Well, the other day, my wandering eyes paid off. I spotted frantic flapping atop a hydro pole and had to pull over. It was definitely worth the stop, as I found myself watching a couple of juvenile Ospreys testing out their wings under the watchful eyes of their parents.

Over and over again they flapped furiously, gaining loft, but holding onto the branches of the nest like a ballerina would a barre. It was truly an amazing moment to witness.

Birds aren’t born knowing how do fly, just like humans aren’t born knowing how to walk. First off, it takes time to develop the enormous pectoral muscles needed to create and sustain the thrust required to get them off the ground and keep them in the air. Although most species lighten the load with hollow long bones and lungs that extend into air sacs throughout much of the body, the muscles responsible for flapping their wings make up 25-35% of a bird’s mass. These take time to develop; how much varies from species to species.  In Osprey, it’s nearly two months.

During that time, they practice, flapping and fluttering awkwardly and sometimes falling altogether. In some species, parents encourage the process by landing farther and farther from the nest with each food delivery, forcing their offspring to come out of their safe haven.

That fragile period in a bird’s life known as fledging is a bit of a behavioural tug-of-war between the demands of the young and the desires of the parents. It’s really not all that unlike human parents trying to get their grown up children to move out. Young birds don’t really want to leave the nest. I mean, why would you? You’re relatively safe, cozy and mom and dad bring you food several times a day. Sure, it gets a little cramped being crammed in there with your siblings and your room isn’t always the cleanest, but you don’t have to go out and work for your food. What’s not to love about that?

The thing is, parent birds need a break by the time young are ready to fledge. They can lose a significant amount of their body mass as a result of the energetic demands of feeding and protecting their offspring. Some species still have time in a season to raise a second brood, potentially doubling their genetic payoff. So, they want to get the kids off and into the world as soon as possible. Scientists have been studying this clash of wills for a long time now, measuring the costs and benefits on both sides of this ‘parent-offspring’ conflict.

When that conflict is resolved depends a lot of the species. Small songbirds usually only spend a couple weeks in the nest and then another couple of weeks following mom and dad around, figuring out how to feed themselves, but still begging for a handout whenever they can. For raptors, the period is much longer; osprey can take up to 17 weeks to become independent. It takes time to learn the art of hunting your own prey.

Young raptors learn by watching and again, through practice. I’m sure that for each generation of raptor there are mice and fish out there who’ve had a few years shaved off their lives from the terror of a near miss by a rookie owl or osprey careening towards them.

Still, they eventually get it right. They have to; at some point, mom and dad decide that they’ve invested enough into this generation and cut the chord. Because, regardless of the species we all must stand on our own two feet.

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Time for a Cool Change

I’ve been getting regular updates lately about a ‘butterfly raising project’ and it reminded me of the one time I was lucky enough to witness this amazing event in nature.

I happened upon this White Admiral (Limenitis arthemis) last summer. I nearly tripped over it, at first unaware of what I had stumbled across. When I looked closely at this newly ‘hatched’ butterfly, drying its brand new wings, the whole thing took my breath away.

It’s a process we learn about as children, one of those uncontested facts that just lives in our brains: caterpillars become butterflies. However, that simple statement doesn’t even begin to do justice to what is truly an amazing process.

Insect life cycles encompass multiple stages that may involve fairly dramatic transformations from larvae to adult (like the previously celebrated fishfly). However, only a few groups of insects other than lepidopterans (butterflies and moths), such as bees, flies and beetles, undergo complete metamorphosis.

It’s a quite remarkable when you really think about it. These lumpy, worm-like creatures that lumber along, munching at leaves transform completely into delicate, colourful jewels that sip daintily at their food, the Victorian lady of the insect world. It happens at the pupal stage, when the larvae (caterpillars) form a chrysalis that then sits suspended for a few weeks up to a few years, depending on the species. From our point of view, it looks like nothing is happening, but on the inside, it’s a different story.

Like most things in animal physiology, the whole process boils down to hormones, the transformation being dictated by the relative amounts of two chemicals coursing through the critter’s hemolymph (insect blood). Just like every other insect, caterpillars moult, shedding their exoskeleton to make room from their growing bodies. Each moult is governed by a hormone called ecdysone (stemming from the word ecdysis, a fancy word for moult). Each new shed produces a larger caterpillar as long as a second hormone called juvenile hormone (thankfully, self-explanatory) is also circulating. It’s basically a chemical that tells the caterpillar to stay a caterpillar.

Then one day, often as a result of changing day lengths or temperature, the caterpillar’s body stops making  juvenile hormone, so when the next moult comes around, things change, the chrysalis is formed and ultimately a butterfly emerges. But how does it go from a wiggling lump to something as complex as a butterfly? Well, that lump was carrying around little spheres of tissue called imaginal discs. These discs truly make the imagined possible, the cells differentiating into eyes, antennae, wings and legs. Each disc has it’s own part to build and if you were to move it to another place on the caterpillar you’d end up with a Picasso painting of a butterfly.

Once the process is complete, the chrysalis splits open and the new adult rests for a bit, drying its wings until it can safely take flight.  The transformation doesn’t only affect what the insect looks like; it’s a complete life change. The metamorphosis from caterpillar to butterfly is a transition from the feeding stage to the reproductive stage and in many cases, that transition is absolute. Luna moths, for example, are like fishflies; once they reach the adult stage, they can no longer feed and their sole purpose is to mate in the day or so they have left before their metabolisms burn out. Of course, not all lepidopterans are as short-lived as adults. Some, like the Mourning Cloak actually hibernate at the adult stage, while Monarch adults travel thousands of kilometres.

So, why go through all that trouble? Why not stay a caterpillar? I’m not sure there is a definite answer to that and I’m sure it’s fuelled many debates among evolutionary biologists. Personally, the fanciful side of me likes the idea that a caterpillar decided one day that he wanted to fly. I think we all have days when we wish to break out of our shell and I think a little change, now and then, can be a good thing.