Category: Group Project

Participants: Mildred Chamblee, Rebecca Marks, April McCrae, Jherimechee Womack, and Melanie Revere

Site: La Selva

Keywords: Carollia brevicauda, Piper auritum, frugivorous
 

Summary:

We observed the feeding habits of Carollia brevicauda to discover if the bats distinguish fruit maturity by position on the tree. It was speculated that, if presented with ripened Piper fruits that were erect or pendant, the bats would choose those in the pendant position.
 

Introduction:

Fruit eating bats such as Carollia brevicauda often concentrate their feeding activity within the understory of the rain forest where they feed on fruiting shrubs and treelets especially those from the genus Piper (Emmons 1997). Piper Auritum, a plant often foraged by C. brevicauda, exhibits a change in fruit morphology from one developmental stage to the next. A flowering bud grows in an erect position; however, as the seedpod begins to mature it drops into a pendant position.

We hypothesized that C. brevicauda chooses which fruits of a Piper auritum plant to eat based upon fruit position along tree limbs. In testing this hypothesis we found that, though the plant does exhibit unique flowering behaviors, C. brevicauda is not using this variable to decide which fruits are ripe and which are not.
 

Methods:

To determine how these bats choose their food, we needed to capture them and monitor their eating habits. To prepare the observation area, two Piper auritum plants were suspended from the ceiling of a shade house using string cords and wire. They were placed parallel to one another with the fruit on each branch in a different locale (one erect and the other pendant). To test the hypothesis, all fruits were stripped from the P. auritum branches. Fourteen centimeter ripened fruits were reattached by drilling a hole in the branch and taping the fruits in place. The fruit height on both plants was measured at 166 centimeters from the floor.

To catch the bats we used three mist nets staked into soft soil. The mist nets were positioned in three locations near STR (Sendero Tres Rios) 800 approximately 100 meters apart. The nets were set up during daylight hours and left closed until dusk. They were reopened at dusk each night to capture bat specimens. On the second night, the nets were placed in different locales so the bats would not avoid capture. Bat specimens were collected, identified, and placed in numbered bags for transport to the observation area. Each bat was weighed using a 100 gram spring scale, and the forearm and tibia of each bat was measured using a metric caliper. One bat was released every hour and checked every thirty minutes for foraging of the Piper auritum fruit. Upon observation, the plant decoys were re-established and an additional bat was set free in the shade house.
 

Results:
 

 
On the very first night, it was observed that a C. brevicauda will eat a ripened fruit regardless of its position on the plant. This disproved our hypothesis but provided insight regarding the bat’s eating habits. It is apparent that choice of ripened fruits is based on factors other than position.
 

Discussion:

The diet of the bats we were testing seemed to consist mainly of the fruit from the Piper auritum plant. Most frugivorous bats will pick the fruit off a tree and fly back to their roost or other safe place to eat. The entire fruit of this species of plant is too large for the bat to be able to carry all of it at once. Because the flower on P. auritum bends into a pendant position once the fruit is ripe, we speculated that there is a correlation between fruit position and the bat’s eating habits. The pendant position of the fruit would provide a convenient place for the bat to roost as it ate. This did not appear to be the case.

During our test, the second bat released into the shade house on the first night was observed eating the erect fruit. This seemed to immediately disprove our hypothesis, but we continued the test for an additional night. One of the erect fruits and one half of a pendant fruit were eaten during the first night’s testing. None of the fruits were touched on the second night. Human error led to the inadvertent feeding of the bats on the second night by a scrap of fruit left lying on the floor. Acceptance of fruit from the floor also seemed to disprove our proposed hypothesis.

Another variable that may have affected our results was the amount of ambient light available. The second trial included the presence of a nearly full moon. After the rains had plagued our tests on the first night and had minimally affected our test on the second night, the clouds cleared and it was quite bright outside. This could have lead to the roosting behavior displayed by the bats on the second night.

Upon completion of the project, we feel that the position of the fruit on the Piper auritum is not a significant cue to the bat. Continued explorations may reveal other cues for fruit ripeness such as color or odor.
 

References:

Emmons, Louise. Neotropical Rainforest Mammals. University of Chicago Press, 1993.

Gentry, Alwyn, H. A Field Guide to the Families and Genera of Woody Plants of Northwest South

America. Convention International; Wash., D.C., 1993.

Krichen, John C. A Neotropical Companion: An introdution to the Animals, Plants, and Ecosystems of the

New World Tropics. Princeton University Press; Princeton, N.J., 1989.

Teaching Applications:

While our project did not support our hypothesis, it was still a valuable learning tool. It gave us experience testing a mammal in a controlled setting that we could adapt to our classroom. It taught us a valuable lesson about how careful you must be in your set up. We thought we had controlled all of our variables, but new ones, like the moonlight, kept appearing.