Cross-Pollination: The Many Faces of Agave Visitors

While my project focuses on nectar-feeding bats and agaves, there are MANY other animals that make use of and benefit from agaves, some of which I have caught on camera!

First off, there are insectivorous (insect-eating) bats that take advantage of all the nocturnal insects flying around the agave flowers and feeding from the nectar. Moths and beetles provide a smorgasboard to these insect-eating bats. I managed to get some infrared videos of one of these visitors in the desert scrub ecosystem of Coahuila. From the still-shot beloow, it looks like this visitor is a Pallid bat (Antrozous pallidus), a fairly common desert bat found in the western U.S. and much of Mexico. These bats are super cool because they typically glean prey off of surfaces, and even ambush large centipedes and scorpions on the ground!

See the large ears? Pallid bats use them to listen for

insect prey crawling on the ground, where they ambush

the unsuspecting insect.

You can even see an eye in this photo!

So how can you tell the difference between an insectivorous bat and a nectarivorous bat on my infrared camera videos? First there are the physical differences. The Pallid bat above has very large ears, while the nectarivorous bats that visit agaves in this region (the Mexican long-nosed bat (Leptonycteris nivalis), the Mexican long-tongued bat (Choeronycteris mexicana), and the Lesser long-nosed bat (Leptonycteris yerbabuenae)) have smaller ears. Another distinguishing feature seen in the above photos of the Pallid bat is the tail membrane, or uropatagium. The Pallid bat has a fairly large tail membrane that kind of looks like it’s wearing a skirt. Below is a nectarivorous bat, which has a very reduced tail membrane (you can see the deep V between the legs). But is this nectarivorous bat a Mexican long-tongued bat (Choeronycteris mexicana) or one of the Leptonycteris species? To answer that question, we again turn to the tail membrane. Choeronycteris has a larger tail membrane than the other two (although not quite as large as the Pallid bat). So, at least from these infrared videos and photos, it looks like the bat below (taken at an agave last summer) is a Leptonycteris. (Identifying the exact species (either Leptonycteris nivalis or Leptonycteris yerbabuenae) from these photos/videos alone is difficult, since the main ways you tell them apart are by comparing their body sizes (nivalis is a bit larger) and whether the edge of the tail membrane is covered in short hairs (in nivalis it is, in yerbabuenae it isn’t).

The V between the legs means that this bat has

a relatively small tail membrane and is therefore

likely a Leptonycteris.

In addition to the tail membrane, the nose length is used to distinguish Choeronycteris from Leptonycteris. Choeronycteris has a much longer and narrower nose than either of the Leptonycteris species, as shown in the photos below.

Left: Leptonycteri, with its shorter and more rounded nose (photo from http://www.arkive.org/southern-long-nosed-bat/leptonycteris-curasoae/). Right: Choeronycteris, with its longer and narrower nose (photo from http://www.arkive.org/mexican-long-tongued-bat/choeronycteris-mexicana/)

What about behavior? Can you tell insect-eating bats from nectar-feeding bats by their behavior? You sure can! Insect-eating bats typically circle an agave several times and flutter more in their flight, while nectar-feeding bats may circle but are much more direct in their approach. Because insect-eating bats are looking for and chasing after flying insects around the agave flowers, they need to zig zag or flutter in the air sometimes to find the insect. However, the food (agave flowers/nectar) of nectar-feeding bats is stationary, so the bats can fly directly to the flower in a straight path. Also, you can often hear this difference in behavior when you’re sitting near the agave. When the nectar-feeding bats fly directly to an agave flower, you can often hear a “whooshing” of their wings as they fly quickly by you. You typically can’t hear the wings of the insect-eating bat. Finally, at least with the Pallid bat that I observed, you could hear audible “feeding buzzes”, which are echolocation pulses in rapid sequence that the bat uses as it gets close to a prey item.

To see these behavioral differences for yourself, check out the videos below!

An insectivorous bat (Pallid bat) circling the agave in search of its next meal.

Nectar-feeding bats (Leptonycteris) quickly touching the agave flowers to lap
up the nectar. These bats can't hover very well like hummingbirds can, so they
must try to lap up as much nectar as possible with their tongues on each pass.

Finally, nectar-feeding bats often “lick their lips” (or tongues) after feeding from the nectar, as you can see in the photo below where the bat has its tongue sticking out slightly!

A glimpse of the tongue as the bat licks its lips!

Bats, however, are only part of the story. There are SO many other animals feeding from or living in/on agaves! There are the numerous insect species that benefit from agaves, including bees, wasps, and flies that feed from the nectar, and ants that live within the agave leaves. Quite a few bird species eat either the nectar or seeds from the flowers, and woodpeckers hollow out the dead stalks for their roosts. I’ve even seen vultures roosting at the tops of dead agaves at night. Then there are the mammals (besides bats). Last year I saw a Ringtail, a member of the racoon family, climb to the top of an agave at night and munch away on the flowers. And this year I caught a little mouse in the act of eating the flowers/nectar too!

A mouse also takes advantage of the agave flowers!

Some of the many avian visitors to agave flowers, to eat either the nectar or the seeds once the flowers are dry (from left to right): Acorn woodpecker (Spanish: Carpintero bellotero, Melanerpes formicivorus); Painted redstart (Myioborus pictus); and a Blue-throated hummingbird (Lampornis clemenciae (thanks Arnulfo Moreno for the identification!)).

A woodpecker has made its nest in an old, dried agave stalk.

And let’s not forget about the domesticated animals that make use of agaves! Cows and goats sometimes eat baby agave plants or the leaves of older agaves in times of drought when other food is not available. From my interviews with community members, it seems like the livestock prefer to eat prickly pear cactus to agave leaves when both are available (apparently cows’ tongues are quite thick and the cactus spines don’t bother them, while the larger, thicker agave spines are harder for them to eat, and also agave leaves are much tougher and more fibrous than succulent cactus). However, I’ve noticed that in some communities there are not a lot of cactus plants, so in these communities the livestock probably rely more on agaves during those drought times. Also, in some communities, people cut some leaves off adult agaves, cut them up, and/or grind them, and feed them to their cattle. Sometimes people also cut the flowering stalks and feed the young flowers to their livestock, again mainly in times of drought.

With all these visitors, both diurnal and nocturnal, we can see just why agaves are considered keystone species in ecosystems. So many other species rely on agaves for food and shelter, and without agaves the ecosystem would be drastically changed. So the next time you have a drink of tequila or mezcal, take a moment to think about the important roles that agaves play in healthy ecosystems!