November 19, 2012 Bats Respond to Global Warming, More Females
In March 2012 over 15,000 warm temperature records were shattered across the United States. The average temperature of 51.1 degrees F was 8.6 degrees above the 20th century average for March and 0.5 degrees F warmer than the previous warmest March in 1910. In addition to disrupting plants, it turns out that these warm temperatures profoundly impacted pregnant bats.
The early spring and above normal temperatures caused bats to produce twice as many female babies. Scientists believe that the females are more likely to survive and then reproduce a year later — as one-year-olds, compared to later born pups.
Other mammals like gray-tailed voles and some birds, for instance parrot finches have an ability to adjust sex ratios of their offspring. In humans, billionaires produce more sons than daughters.
Bats are crucial insectivores. They are the only mammals capable of flying. Their wings consist of a double membrane adjoining a bony structure resembling a human hand. The extra long fingers and membrane run downward to include a tail. Only the thumbs are free, and the thumb claws are used for climbing and turning around during roosting (or perching). For bats, that means hanging upside down.
When most animals hang upside down, blood rushes to the head; but not in bats. They have special valves in their veins to keep the blood moving through their bodies when inverted.
How much energy do bats use to fly? Lots. On average bats flap their wings between 10 and 20 beats every second and they reach speeds of between four and 22 mph. In order to achieve these speeds, their heart must pump at about 1,000 beats per minute.
Bats have learned to compensate for high-energy needs by lowering their body temperature. They have an internal adjustable thermostat, when inactive body temperatures fall from 113 to 41 degrees F. Heart rates drop from 100 to 200 beats per minute while resting and to five beats per minute during hibernation.
To hibernate, bats must have a 40% fat reserve. It’s a good thing that bats are excellent hunters. One bat can eat up to 600 mosquitoes in an hour. They also feast upon moths. In Central Texas 100 million Mexican free-tailed bats eat 1,000 tons of moths each night. A 2006 study calculated that the bats saved South Central Texas cotton farmers in 8 counties $741,000, which would otherwise have been allocated to man-made insecticides.
To catch insects bats use echolocation, or sonar, to locate their prey. In addition, bat sonar enables navigation with ease in total darkness. High frequencies are emitted from the voice-box and when the waves hit an object the bats’ sensitive ears hear echoes and differentiate between trees, rocks or prey.
All nature’s creates have marvelous adaptations and moths are no exception. They have evolved fine hairs, which detect bat sonar. When a bat hunts for a moth it is analogous to high-tech warfare between modern fighter planes. Moths are able to zig-zag and free fall like sky-divers. When moths free fall, bats somehow calculate the angle of incidence and make a pouch using their tails to form an inverted scoop, often catching their prey. And once caught, they rapidly chew the moth up to seven times per second.
Bats like all creatures are susceptible to droughts. Last year (2011) the Mexican free-tail bat population felt the bite of the brutal drought as their numbers declined from Austin to San Antonio.
The challenge for all life will be adapting to the forecasted droughts in the coming decade(s). According to the National Center of Atmospheric Research and its 22 computer models, the western two-thirds of the United States can expect more prolonged droughts accompanied by warmer temperatures.
Text © by Dr Reese Halter 2012. All rights reserved.
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