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NECTAR EATING BATS IN SOUTHERN ARIZONA

 by Sandy Wolf 

Two species of nectar-feeding bats, the lesser long-nosed bat and the Mexican long-tongued bat, forage at hummingbird feeders in parts of Tucson and other areas in southern Arizona. Both species belong to the family Phyllostomidae, which comprises mostly tropical species. They are called leaf-nosed bats because they have a triangular-shaped flap of skin on their nose. Both species are mine/cave obligates, which means during the day they roost only in caves or abandoned mines. They are very sensitive to disturbance at their roosts. Both species have relatively large eyes and thus good vision.

Muzzle is short and conical

Lesser long-nosed bats 

Lesser long-nosed bats (Leptonycteris yerbabuenae), or leptos for short, are about 2.5-3 inches long with a wingspan of about 14 inches. They migrate into west-central Arizona from Mexico in April and gather in large maternity colonies of thousands of females to give birth and raise their young. Each bat gives birth to a single young in May or June. Leptos feed on the nectar and pollen of columnar cactus such as the saguaro and organ pipe cactus. They pollinate these plants as they travel from flower to flower with pollen-covered faces and heads. They eat the fruit they helped produce, and spread the seeds as they fly or hang up in a tree to digest during the night. A maternity colony formerly occupied Colossal Cave, southeast of Tucson; however, today all known maternity sites are west of Tucson.

No tail membrane (pajama legs)

Beginning in July, leptos appear in southeastern Arizona and form late-summer roosts, mostly of adult females and young of the year. Roosts are in areas of desert-scrub, desert grasslands, and up into oak woodland habitats. Bats feed on the nectar and pollen of agaves and then depart for Mexico, usually in September-October.

Leptos can travel 30 miles to forage, although probably most go no more than 15-20 miles. In southeastern Arizona, radio-transmittered bats were found to spend most of the night foraging, going to the same area each night. Between foraging bouts, they hang up in a night roost to digest and rest. Night roosts can be in man-made structures such as porches, barns, and bridges as well as caves, mines, and trees.

Mexican long-tongued bats

Muzzle is long and cylindrical

Mexican long-tongued bats (Choeronycteris mexicana), or choeros for short, are about the same size as leptos. They migrate to southern Arizona from Mexico in late spring, typically roosting in Madrean evergreen woodlands or semidesert grasslands, and up to elevations of pine-fir forests. A survey of historical roosts found that roosts occupied in 1999 were associated with surface water and riparian vegetation, and were near agaves, which are a major food source. Choeros form small maternity groups, usually of a dozen or less, but occasionally up to 50 adults. Young are born in June-July, and can fly in about 3 weeks. Unlike leptos, which often roost deep in a mine or cave, choeros are often found near the entrance, and if disturbed, will fly out into the open rather than deeper into the shelter.

Little is known about this species. In the Tucson area, choeros have been observed at hummingbird feeders throughout the winter, so not all migrate to Mexico in the fall. They have longer tongues than leptos, and may be able to exploit a wider variety of food plants. 

Tail membrane extends
about halfway down legs

The two nectar-feeding bats in Arizona are very difficult to tell apart while they are flying to and from a hummingbird feeder. If you have night-vision equipment, you may catch a glimpse of an identifying feature. You can also record them with a Sony Night Shot camcorder with extra infrared light and play back the video in slow motion. The difference in their muzzles is somewhat subtle; identification is easiest if you have both species to compare.The bats are most easily distinguished by differences in their tail membranes.

 

 

 

 

 


Sandy Wolf (M.S. Wildlife Ecology) is a wildlife biologist specializing in bats. For the last 10 years she has been a private consultant and partner of Bat Research and Consulting. Studying issues relating to bats in urban areas is one of her interests; she studied the bats that live in bridges in Tucson for her master's project, and initiated the hummingbird feeder monitoring project for nectarivorous bats that has been continued by Arizona Game and Fish, Marana, and Tucson. She also provides assistance and education to homeowners who have questions about bats.

In addition to performing work for agencies, universities, and other researchers, she has conducted her own research and conservation efforts for bats. Projects include surveying mines and caves to locate bat roosts, assessing threats to these sites, protecting bats and people by building "bat-friendly" gates that allow bats access but keep people from entering unsafe mines, and studying which gate designs are best for different bat colonies. She has experience going underground in mines and caves, which requires proper safety equipment and training, tracking foraging bats through the night with radio-telemetry, and monitoring colony numbers and behavior at roosts using infrared-sensitive cameras.

She has given numerous educational presentations to Tucson public groups as well as scientific presentations at local, national, and international professional conferences. She is a member of community and professional organizations that promote bat research and conservation. 


From: wildbirdstore@msn.com
To: Sandy Wolf
Subject: bats & bat article
Date: Tue, 27 Sep 2011

Sandy, received your bat article and really enjoyed reading it. I see no need to change anything so we'll print it as is. I think the pictures showing the differences in the membranes to distinguish the species is great. However, I have some questions. Are there any negative drawbacks in feeding nectar to these bats. Will it prevent them from foraging on natural plants? Is it the 1st cold nights that cause them to migrate south? Or, do their hormones also play a role in determining when they migrate - as they do with birds? Do Bat biologists get preventative rabies shots knowing they will be handling them? Is that why they can handle them with bare hands? Can nectar bats bite through human skin?

You mentioned to me that you would be interested in filming bats at our feeders in the future. Since I've talked with you there has been a steady increase in the number of bats I'm providing nectar for. I estimated that perhaps at that time I was attracting possibly up to a dozen or so bats. However, since then, I have noticed a steady increase in their numbers. I now think I have at least twice as many bats as I did a month ago. I was putting out about 36 ounces of nectar a night but now I put out that much nectar or slightly more than that at twilight and again the same amount after midnight. By midnight they have usurped everything from each of the feeders so I replenish them with fresh nectar again around midnight. I used over 80 ounces each of last several nights. How much can a single bat consume? How many, can you estimate, bats do you think I have based on that information? I've tried counting them as best as I can but it is a daunting task. I think I've seen as many as twelve to fifteen at once at my feeders. I have 7 feeders they can easily use. Last night I timed how many hits on a single feeder in a single minutes's time. I had 26 hits in almost a full minute.

Any guesses to how many I have? How many times in a single minute will a single bat hit the feeder? I hope you don't think these questions are a waste of your time to answer. I know you are busy and wouldn't want to waste time on things you thought frivilous, but these questions are serious questions for me to ask and who better to ask them to but you. Thanks for your time and support. I remain, very respectfully yours, Jon

From: Sandy Wolf 
To: wildbirdstore@msn.com
Subject: RE: bats & bat article Date: Wed, 28 Sep 2011 

Hi Jon, I'm out of town now, so this will be a quick reply. You raise good questions. Yes, bat biologists need pre-exposure rabies shots. It's possible for most any bat here to break the skin. Usually I use one glove for them to gnaw on and one ungloved hand for dexterity in handling. In my opinion, it's rather foolish not to use gloves at all.

I don't think anyone knows if feeders would delay migration or change natural foraging patterns. My hunch would be no for the migration, they rely on other cues. Weather patterns could be a proximal cause for a wave of migration- it's been documented in free-tails at least and makes sense for tropical species.

There are many more bats roosting in the Rincons than usual this year which would account for your multitude of bats. To answer your questions about use of a feeder you'd have to mark individuals, and then have a way to detect marked individuals. I'd love to work on that- just need funding.

hope this helps 

Sandy

Sandy Wolf Bat Research and Consulting Tucson, AZ


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