This is a fascinating interview with marine scientist John Durban, who explains how his team is using drones to monitor the health of killer whales in the waters off the coast of California. The best part is that he shows us how to understand what we're seeing in aerial photographs of the whales.

Some of the news is sad, because declining salmon populations mean that a few of these whales appear to be staving to death. But there is good news, too: We see a very pregnant whale, along with a healthy baby and juvenile.

From the story, by Rich Press of the U.S. National Oceanic and Atmospheric Administration's fisheries division:

The main question scientists are trying to answer is: Are the whales getting enough to eat? To find out, they fly the hexacopter at an altitude of more than 100 feet, high enough that the whales don't notice it, but near enough to get photographs that are incredibly revealing. Scientists have previously taken aerial photographs of killer whales from a helicopter, but those photos are taken from a much higher altitude, and the cost can be prohibitive.

By analyzing the hexacopter photos, scientists can see how fat or skinny individual whales are. They can also see which whales are pregnant and what percentage of pregnancies are carried to term.

Currently, scientists do a summer census to learn out how many whales have died since the year before. "But mortality is a pretty coarse measure of how well the population is doing because the problem, if there is one, has already occurred," said John Durban, a biologist with NOAA's Southwest Fisheries Science Center in La Jolla, California. But the hexacopter, Durban said, "can give us a more sensitive measure that we might be able to respond to before whales die."

Read more via NOAA.