Biology 103
2002 Second Paper
On Serendip

Owls are notoriously wise birds; they know how many licks it takes to get to the center of a Tootsie Roll pop, they are Winnie the Pooh's best advisors, Harry Potter's messenger friends, and even Bryn Mawr's semi-mascots. Being so advanced, they are also a part of animal adaptation and evolution. Because I know next to nothing about owls, I decided to undertake some snowy owl reproduction research. The question I set out to answer was: "How do snowy owls reproduce, and how does that relate to an adaptive process to evolution?", because I know that there must be a clever way for these intelligent old birds to produce offspring. I just do not know what this method is.

Snowy owls' reproduction has many phases, including courting, mating, egg-laying, nest-building, taking care of the young, and the young leaving the parents' nest. Each of these illustrates how evolved and adapted to their environment owls are.

Male snowy owls apparently have a mating call and ritual procedure which involve courtships beginning in midwinter, and which last through March and April, distanced from the breeding grounds. To attract the females, males will take off in exaggerated flight patterns while hooting loud, booming, repeated calls, or they will stand in open-wing postures, with the wings closest to the females angled slightly towards them, attempting to receive some attention. Their mating cries can be heard up to six miles away, in the tundra region where the snowy owls reside. When the males see the females, they will swiftly snatch a gift lemming with their claws. They will land and place it somewhere visible to the females. Males may then push the gift towards females, or spread their wings and waddle around the victim, concealing it. To satisfy still uninterested females, the males may take off for more lemmings. They often feed their catches to the females. On the ground, males will "bow, fluff their feathers, and strut around with wings spread and dragging on the ground." (6)

Perhaps these rituals are not as "sophisticated" as that of humans, but this does seem survival of the fittest to me. Owls have a proper courtship, away from reproducing responsibilities. Males must display their assets and give presents in order to win the females over. Females obviously have criteria for their partners and evolution has taught them that they need partners who surpass others of their kind.

When the females are finally content with the males' courtship attempts, the couple fly off, soaring up and down through the sky. The males sometimes swoop to catch more lemming and pass their game to the females. They begin mating and breeding in April to May. Because they are a class of birds, snowy owls lay eggs.

The egg-laying process in itself is a sign of evolution. Female snowy owls typically lay five to eight white eggs in a clutch, and sometimes up to fourteen, depending on the lemming population. Around every four years, there is a predictable thinning of lemming numbers, and the owl pair may not breed at all. If a first egg clutch is unsuccessful in hatching, the couple probably also will not renest for the rest of the year. The reproduction quantity thus relies on the fickle prey population, which is an agile adaptive system indeed. In this way, there is almost one hundred percent nesting success achieved by the snowy owls.

Eggs are laid about every other day, so that the older and stronger chicks will have advantages in time periods when there may be a shorter food supply later (they will consume most of the food their parents bring, and may possibly even slay younger siblings and eat them). The females incubate for about thirty-one to thirty-four days, keeping the eggs warm, while the males guard the nest and do all of the hunting and bringing in of the food. The survival of the fittest ideal is incorporated inside the species' competition with proper care by parents from other predators, while the babies are still un-hatched. Offspring may compete between each other, even to the death, but intruders are not allowed to interrupt the growing process.

To build a nest for their eggs, snowy owls make a hollow on the exposed, snow-free, dry tundra ground with shallow talon scrapes approximately three to four inches deep and one foot across, on top of an elevated rise or mound. Gravel bars and abandoned eagle nests are occasionally frequented. The nests are almost exclusively made on the ground, lined with moss, lichens, feathers, scraps of vegetation and their own feathers. Sites are near good hunting areas, commanding a view of surroundings. Some areas are only used once for breeding, but other areas are occupied for several years at a time. Territories around the nests range anywhere from one to six kilometers, and do overlap with other pairs' regions.

Clearly, this is a well "thought-out" plan for the parents to keep their young safe and sound. They even consider where they will have easy access to food, but will be difficult to find. Evolution has made this a habit, or else the owls would not survive.

Snowy owl eggs begin hatching one by one, over the interval of a month. Owls have adapted to the shell life, by gaining temporary incisors for cracking through eggs. They employ temporary "egg teeth" to crack through the shells. The chicks are blue-grey while they stay in their hole in the ground, and will be covered in a snowy-white down and face around three weeks after hatching success. At the same time (about sixteen to twenty-five days), their primary wing feathers will grow in, and they may begin to wander away from the nest. But this is before they can fly, and so both parents feed and tend to the young until then.

Both the male and female owls will feed, protect, and bring up their chicks until their babies are ready to fly away and hunt on their own. Nestling owls take about two lemmings per day, but a family of snowy owls may eat up to one thousand, five hundred lemmings before the owlets may be able to scatter. Because they are so defensive, snowy owls may aggressively attack intruders up to one kilometer away from their nest sites. Males will sometimes fight in midair, and females may defend their territories or potential mate against other owls of their sex. Males may defend their young using a "crippled bird" act to lure predators away from nests. They have developed scenarios in order to survive.

Owlets fledge in about forty-three to fifty-seven days, in which they also become able to search and hunt for food themselves. The young clearly require an entire summer's worth of special care by the owl parents. Adaptation has made snowy owls smart reproducers with wise habits and precautions.

References

1) Enchanted Learning
2) Lady Wild Life's Endangered Wildlife
3) Minnesota Department of Natural Resources
4) Oregon Zoo Animals
5) Ross Park Zoo
6) The Owl Pages , Information About Owls
7) Tribune-Review
8) University of Michigan


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