Monday, May 20, 2013

The Northern Hawk Owl

The Northern Hawk Owl is adept at capturing rodents
under the snow due to their great hearing.

The Northern Hawk Owl is a non-migratory owl that resembles a hawk in behavior and appearance. During flight it looks similar to a Cooper's Hawk. It is one of the few owls that is primarily active during the day.
   Northern Hawk Owls are unevenly distributed throughout the boreal forest. They live mostly in open coniferous forests, or coniferous/deciduous mixed forests of Canada and Alaska, sometimes extending down to other northern states during winter or after a population explosion in their prey. They are also found across northern Eurasia, reaching Siberia at its eastern range. 
   Their prey includes small rodents (usually voles) snowshoe hares, red squirrels, and a variety of birds. During winter, they prefer to feed on ground-dwelling birds such as grouse and ptarmigans. The Northern Hawk Owl's fortune rises and falls with its prey. During prey population explosions, their numbers can swell to more than 50,000 breeding pairs, but if food is scarce, their numbers dwindle accordingly.
   The hunting strategy for the Northern Hawk Owl is to perch on a spruce tree in open forest and scan the immediate area for prey. If nothing is found, they move on to another location. When prey is spotted, the owl attacks by going from a horizontal position into a gliding dive. If the prey is further away, the bird will flap its wings a few times during the dive to make up the extra distance. This owl has superb hearing and can plunge into snow to capture rodents beneath the surface.
   The Northern Hawk Owl is one of the least studied birds in North America. They are hard to study because of a low, fluctuating population density and remote breeding locations. This lack of knowledge makes it nearly impossible to accurately estimate the population levels of this species.
   Northern Hawk Owl densities are estimated to be at most six pairs per 100 sq km. But because they live throughout the boreal forest, the North American population is thought to be quite large. In North America, over half of their breeding territory occurs in non-commercial boreal forests, so as long as nothing threatens this habitat, the species should be OK even though the populations seems to be declining. Improved monitoring should be a high priority so that we can be more confident in that assessment.

Monday, May 13, 2013

Centrifugal vs. Centripetal

I went to my daughter’s open house at school last Friday and afterwards we played a bit of tether ball before heading home. And while I’m not that great at tether ball, I can explain the forces involved in the game.

   Centrifugal force is what is often used to describe what happens to the ball as it rotates around the pole—it’s being pushed as far away from the pole as possible. But in actuality, centrifugal force is a fictitious force. The only force being applied to the ball, pulling it toward the center of rotation, is a centripetal or center-seeking force. There is nothing actually pulling the ball away from the string, what you have is just inertia as described by Newton in his First Law of Motion: An object at rest remains at rest unless acted upon by a force and an object in motion remains in motion—at a constant velocity—unless acted upon by a force. 
   Newton based his first law on the work of Galileo, who described what he called the Law of Inertia: “A body at rest remains at rest and a body in motion continues to move at constant velocity along a straight line unless acted upon by an external force.” Until Galileo, it was thought that one must exert a force in order to keep an object in motion. Galileo recognized that the reason moving bodies eventually come to rest is because of resistance forces such as friction. Without friction, bodies would continue to move at constant velocity. But I digress…
   So if you were to cut the rope as the ball is rotating what would happen? Some might think that the ball would fly away from the pole, but that’s not correct. The ball would actually move perpendicular to the pole, due to inertia. The centripetal force of the rope works against inertia by keeping the ball from travelling in a straight path. It is this constant struggle against inertia that makes it seem that the ball is trying to move away from the pole. What we call a centrifugal force is actually just the effect of inertia working against the centripetal force. Your welcome.

Monday, May 6, 2013

The Rose of Saturn

Recently, NASA release an incredible photo of Saturn’s north pole showing a massive spinning vortex of a storm they dubbed “The Rose”. This false-color image taken by the Cassini spacecraft shows the storm spanning a 2,000 km diameter which, by comparison, is 200 km wider than Hurricane Sandy. Maximum wind speeds of 530 km/h have been calculated—that is some hurricane!
   See how much you know about the ringed planet by answering these ten quiz questions, below. Good luck!