Journey North News

Lesser Long-Nosed Bat Migration Update: May 2, 1996

News of the first lesser long-nosed bats' arrival in the U.S. is expected any day. While we're waiting, don't forget to report sightings of bats in your region by sending a Field Data Form to Journey North. Simply press the blue button below labeled "Report Field Observations" or send an e-mail report to:

Have you ever wondered:

Today our bat expert Ginny Dalton discusses these things. Her report is full of math facts which we hope you'll enjoy. Read carefully so you can answer today's Challenge Question:

Challenge Question # 104

(To respond to these questions please follow the instructions at the end of this report. )

To: Journey North
From: Ginny Dalton

How Much Energy to Operate a Bat?
Let's look at how much energy is required by an adult Lepto. Here's an animal with a big energy demand for its size! (Now, nobody has ever measured this exactly for Leptos, but we can use information about other bats and extend the results logically.) It takes roughly 20.2 kcal to maintain one of these bats for a day. A Lepto uses about 100 times less energy in a day than a human does, as you can see on the chart below. But it weighs 2,000 times less. Obviously it takes more energy to operate an ounce of bat that an ounce of human! Why? Well, for one thing, bats fly and the energetic cost of flight is high.

Human......2,000 oz......2,000.0 kcal/day*
Bat........0,001 oz......0,020.2 kcal/day

(*There is confusion in the layman's literature regarding calories. Please read the explanation below.)

Flower Powered Bats
How much energy is available in the nectar of the flowers Leptos visit? It has been calculated that the nectar in saguaro flowers is about 24% sugar. This nectar if very sweet: For comparison, Classic Coke is 10% sugar! Each flower holds about 1.0 ml (milliliter) nectar. A single bat only takes about 0.1 ml with each visit to a flower. A bat's stomach can hold about 4 ml of fluid when full. Of those stomachs measured, 3 ml are sugar water and the remaining 1 ml was pollen.

There are about 4 calories (= 0.004 kcal) in a mg (milligram) of sugar. There is 1.0 mg sugar in each microliter (.001 ml) of nectar. So how many calories in 1.0 ml, the amount a flower holds? If a bat drains an entire flower, how many visits would the bat have to make to the flower? And how many total calories would it get from that single flower?...(Don't forget to multiply your answer in cal/ml by 0.24 since the nectar contains only 24% sugar.) I got 960 cal (0.960 kcal) in a single flower that contains 1.0 ml nectar.

So, since a bat takes about 0.1 ml for each visit, a bat would have to visit about 10 flowers to get those 960 cal. How many flowers total does a bat have to visit to sustain it for one day (20,200 cal = 20.2 kcal)? Assuming 8 flowers per saguaro per night, how many saguaro plants would have to be visited? Now, assuming about 30 seconds per visit to a flower (that included transit time to the flower) for one sip (0.1 ml nectar), how long does that bat have to be flying to obtain the required number of sips to maintain it for a day (24-hr period)?

The information above is all you need to answer today's Challenge Question. Good luck!

There is not enough information available for calculating the exact requirements for pregnant females, but a near-term fetus of a 22- gram female bat can weigh as much as 8 grams. Each female gives birth to a single young each year. Carrying that heavy a load can require about 40% more power for flight. Of all the calculations conducted on females during the various reproductive stages, lactation (when the young are nursing) is the most energetically demanding on the female.

Before my next report, think about this: