High in the Andes Mountains, the Peruvian long-nosed bat helps sustain a critical food supply for a fragile ecosystem . . .
High in the Andes Mountains, the Peruvian long-nosed bat helps sustain a critical food supply for a fragile ecosystem . . .
By Catherine Sahley
I sat quietly outside the abandoned mine, waiting for the bats to fly out and begin their night of foraging--seeking out the nectar and fruit of Peru's desert cacti. From my observation post midway up a ridge, I had an excellent view of the evening scene around me. Directly below the snow-capped peak of the Misti volcano, the city lights of Arequipa glowed brightly. Beyond that, along the Andean cordillera, I could see the fading plume of ash that had recently erupted from another volcano, the Sabancaya. Surrounding me, and spread out over the ridge and valley below, columnar cacti were silhouetted like sentinels against the darkening sky.
Just at the moment when twilight turned to night, I heard the sound of flapping wings, a sound magnified by the otherwise complete silence of the desert. A bat flew out of the mine, approached the nearest cactus, and hovered at an open flower to drink nectar before disappearing into the darkness. Although I sat and observed the mine entrance for a while longer, no more bats flew out.
The solitary bat I observed contrasted with my observations of the previous year, when I had counted 10 bats exiting the mine. I signaled with my flashlight to my colleague, Luís, who had been sitting 40 feet away, watching a second entrance to the same mine. He climbed down the ridge and told me that he had not seen or heard any bats. I wrote in my field book, "one bat, exited at 6:15 p.m." Then we drove to the one-room adobe hut that had once served as housing for miners but now was our desert field station.
I had traveled to Peru the year before to begin investigating the importance of bats as pollinators of columnar cacti in arid habitats along the western Andean slopes of Peru. I chose to work in southern Peru, near the city of Arequipa, because biologists there had found several colonies of a very rare nectar-feeding bat, Platalina genovensium, the Peruvian long-nosed bat. This mysterious bat was first described in 1928 and has since been found only in the arid regions of Peru. Other than a handful of references on where the bat had previously been found, no additional information was available on its natural history or ecology.
The Peruvian long-nosed bat was especially intriguing to me for several reasons. Like most nectar-feeding bats, it has an elongated muzzle and tongue that allows it to gather nectar from flowers that are long and tubular in shape. But this species' muzzle is exceptionally long when compared to most other nectar-feeding bats. Did this feature signify that it was more highly specialized than other bats for feeding on flowers? Also, because the Peruvian long-nosed bat was the only species of nectar-feeding bat occurring along the western slopes of the Andes in southern Peru, it was the only possible bat pollinator and seed disperser of plants in this region. Because of its presumed rarity and potential importance to columnar cacti in Peruvian deserts, I felt that gathering ecological data on the Peruvian long-nosed bat was especially important. So when I learned that biologists in Arequipa had found colonies of these bats near areas where cacti were abundant, I packed my bags to go and investigate.
Once in Arequipa, I spoke with Percy Jiménez, an ecology professor at the Universidad Nacional de San Agustín, and Luís Baraybar, a young, enthusiastic biology student. Luís and his peers had been monitoring Peruvian long-nosed colonies in Arequipa for over a year, and Luís was interested in collecting data on the bats for his bachelor's degree thesis. He agreed to be a field assistant for my study of cactus pollination and, at the same time, collect data for his study on the bats' diet.
Six months later, with funds from BCI, the World Wildlife Fund, and the Wildlife Conservation Society, I returned to Arequipa to begin the study. Arequipa is a city of more than 600,000 people that was founded almost 500 years ago. Located in the "foothills" of the Andes at an altitude of 8,500 feet, the city is surrounded on all sides by desert containing many species of cacti as well as birds, mammals, lizards, and insects.
I was interested in determining how flower visits by Peruvian long-nosed bats influenced pollination and fruit production of columnar cacti and how patterns of flower and fruit production of these cacti influenced bat populations. I decided to concentrate on the most abundant columnar cactus in the desert surrounding Arequipa, the Weberbauer cactus (Weberbauerocereus weberbaueri). These cacti produce long, tubular flowers that open in late afternoon, remain open throughout the night, and close late the following morning. Hummingbirds are the first to visit the flowers in late afternoon, Peruvian long-nosed bats visit them during the night, and hummingbirds visit the flowers again in the morning. After pollination, developing fruits take approximately two months to ripen. When ripe, the fruits burst open, and Peruvian long-nosed bats, rodents, and many species of birds consume the fleshy pulp and seeds.
To learn how important bats were as pollinators of this cactus, I conducted an experiment to exclude certain visitors to the flowers. I placed bridal-veil netting on some cactus flowers only during the day, and on others only at night, allowing me to keep bats from certain flowers and hummingbirds from others. On other flowers I placed wire mesh that excluded both bats and hummingbirds but permitted insects to visit. This procedure allowed me to determine whether insects were also substantial pollinators. After the flowers closed, I checked them weekly to see if fruits developed.
After two months of waiting for the fruits to mature, I could finally tally my results. As I had suspected, I found that Peruvian long-nosed bats were important pollinators of Weberbauer cacti. Seventy percent of flowers that were accessible to bats began to develop into fruits. This contrasted with flowers visited by hummingbirds, where only 55 percent developed into fruits. I was surprised to find that flowers could also produce fruits in the absence of any visitors, through self-pollination; this happened 40 percent of the time. Interestingly, this was the same percentage of fruit produced when insects were allowed to visit the flowers, leading me to conclude that insects were not significant pollinators of these cacti. Although hummingbirds also contributed toward fruit production, my experiments showed that bats were the most important pollinators of Weberbauer cacti.
Luís and I continued to monitor fruit and flower production of the cacti and censused the bats whenever possible. We found that Peruvian long-nosed bats were not very abundant around Arequipa, discovering only seven colony sites, which contained a total of less than 100 bats. The bats often roosted in small groups inside abandoned copper mines located in areas near Weberbauer cacti. They were the only bat species that we found roosting inside these mines though we knew that an insectivorous species, the big-eared bat (Histiotus macrotus), was also present in the area. Inside Peruvian long-nosed roosts, we found many Weberbauer cactus seeds, confirming our suspicions that these bats were eating cactus fruits as well as feeding from the flowers.
Perhaps our most important observation was that Weberbauer cacti have continuous production of fruit and flowers throughout the year, although we did find definitive peaks. Because this is the only plant species at our study site that produces both flowers and fleshy fruits year-round, these cacti are especially important food resources for animals in Arequipa when other plants are not flowering or fruiting. Plants like the Weberbauer, which support or maintain populations of animals during periods of resource scarcity, are often called "keystone" species. Removing these plants, or upsetting their reproductive schedules by removing their pollinators or seed dispersers, can have a ripple effect throughout an ecosystem, possibly decreasing other animal and plant species. Thus, the presence of Peruvian long-nosed bats is especially important in this area because of their promotion of fruit production in these cacti.
As most field biologists quickly learn, nature is unpredictable. My arrival in Peru earlier that year happened to coincide with the occurrence of an El Niño event. El Niño events are climatic fluctuations caused by the warming of the normally cold waters off the coast of Peru. In northern Peru, El Niño causes heavy rainfall, while in southern Peru, it is associated with severe droughts. As the rainy season of Arequipa came and went without any rainfall, I noticed that the number of flowers and fruits produced by Weberbauer cacti was decreasing drastically. Other species of plants at my study site were reduced to dry twigs, and the desert landscape, always stark, took on a parched appearance. Soon after, our censuses of bats revealed that their numbers were decreasing as well, by as much as 90 percent during the most severe part of the drought. I hypothesized that it was likely that most, but not all, of the bats were emigrating from Arequipa in response to the decrease in fruits and flowers available to them.
The 1991-92 drought was long and severe, even by Arequipa standards. The Weberbauer cacti got thinner as their water reserves were used up, but amazingly, some individual plants kept producing a few fruits and flowers even though over a year had passed since it had rained. These were the only plants to do so during this time of scarcity.
It became apparent that these plants were extremely important sources of nourishment for the birds, bats, and other animals that had to survive this period of drought. Without these cacti, many desert animals probably could not have survived until the next rains came. Even the hardy guanacos (Lama guanicoe), wild camelid cousins of the llama, began to eat from the cactus plants during the worst part of the drought, presumably to obtain some moisture. Since these cacti are covered with a thick layer of very long and painfully sharp spines, this feat served to underscore the severity of the situation. The few bats that we found during our censuses that field season were probably depending exclusively on these cacti for food, while contributing to fruit production through their pollinator services.
The first rains in over a year finally came to Arequipa in early 1993. The Misti volcano and the other mountains of the Andean cordillera that tower over the city were graced with a fresh covering of snow. Almost immediately the Weberbauer cacti began to swell up with water, and within a few months, flower and fruit production increased dramatically. Species of plants that I had recognized previously only as dry twigs turned green and began to flower.
Luís and I were hopeful that the Peruvian long-nosed bats would soon return and that our study could go on as planned. But, as the months wore on, our censuses indicated that bat populations were far lower than they had been in 1990 and 1991, when our study began. Were bats pollinating fewer flowers than they had been in 1991? To answer this question, I repeated the pollinator exclusion experiments I had conducted that year and predicted that bat pollination would be responsible for a smaller proportion of fruit production in 1993 than in 1991. As I completed the experiment and began censusing developing fruits, it became apparent that my prediction would hold true.
The results of the two pollination experiments were indeed different. In 1993, bat pollination of flowers was significantly less than it was in 1991. The reduction in bat-pollinated flowers was obviously due to the reduction in bat populations we had observed during our censuses. Surprisingly, the experiments indicated that the proportion of hummingbird-pollinated flowers actually remained similar to that observed in 1991; apparently the drought had not caused a reduction in hummingbird populations. Although fruit and flower production of Weberbauer continued at "normal" levels into mid-1994, bat populations did not return to predrought levels. What was going on?
Unfortunately, I can only speculate as to why bat population levels remained low after the rains returned to Arequipa. Three factors seemed to be responsible for the decrease in numbers over the course of the study. First, bats may have emigrated from Arequipa during the worst part of the drought. It is possible that they flew to northern Peru, where higher-than-average rainfall may have resulted in abundant fruit and flower production of plant species occurring there. If they did relocate, it could be that they simply had not returned. A second possibility is that the prolonged drought conditions may have caused higher than normal mortality for the bats, though I did not find any evidence of increased mortality in Arequipa.
The third factor influencing bat populations is "harvesting" by humans. Some people in rural areas believe that bats have beneficial medicinal properties, and consequently, bats are commonly used in folkloric medicinal remedies. One of the abandoned mines that we censused was sometimes visited for the purpose of collecting bats. In one instance, Luís met two young boys who had made the arduous two-hour walk through the desert to reach the mine. They were regular visitors, they said, collecting bats for their grandfather, who used the blood as an antidote to epileptic seizures. Although Luís explained to the boys that the bats were endangered and should be left alone, we often found footprints near the entrance of this mine.
In 1994, I returned to the University of Miami to write my doctoral dissertation. Although I had collected interesting information regarding the bats and their importance as pollinators in Peruvian deserts, I felt like my research created more questions than it answered. This year I plan on returning to Peru to conduct more research on the status of Peruvian long-nosed bat populations in Arequipa as well as other areas of the country. I hope to involve additional Peruvian biologists in my search for ways to help conserve bat populations. Fortunately, I have met many young, enthusiastic biology students in Arequipa who are concerned about conserving bats, cacti, and the other species of plants and animals that inhabit the Andean foothills surrounding their city. I am hopeful that by working together, we can help preserve this important part of Peru's biological heritage.
Catherine Sahley recently completed her Ph.D. at the University of Miami at Coral Gables, Florida. She has returned to Peru to continue her studies of bat-cactus interactions.
Student Scholarship Awards Make a Difference
BCI's Student Research Program has helped to fund Catherine Sahley's investigation of Peruvian long-nosed bats in the Andes for several years. Her work in this area is especially important because these arid habitats are poorly understood and are underrepresented in the national parks and reserves system of Peru.
Sahley is half-Peruvian and has always had an interest in the country's spectacular biological diversity. In addition to her studies of Peruvian long-nosed bats' relationships with columnar cacti, she and her colleague, Luís Baraybar, have taken every opportunity to teach local citizens about bats.
Their educational efforts have taken many forms. Sahley and Baraybar were crucial in protecting the largest local bat colony, located on the premises of a hydroelectric plant. They sought out the engineers in charge of the facility and persuaded them to limit disturbance at the roost. Sahley also took her knowledge of bats to the media--writing an article in Spanish for an Arequipa newspaper which described her project and discussed the importance of bats and cacti. In addition, she gave seminars at the University of Arequipa regarding the importance of bats in ecosystems. While Sahley was back at the University of Miami working on her dissertation, Baraybar continued to educate people about bats by giving talks, producing exhibits, and speaking on a radio show.
Sahley and Baraybar hope to broaden their study and census of Peruvian long-nosed bat populations throughout the rest of Peru, and they plan to use their information to develop future conservation measures. Because the bats are roosting primarily in mines, one of Sahley's objectives is to work with mining companies to minimize roost disturbance. Sahley's long-term goal is to form an environmental NGO (nongovernmental organization) to further conservation efforts in Peru.
The educational work that Sahley has set in motion is indispensable in teaching the people of Arequipa to value their bats as important ecological assets. With enthusiastic assistance from fellow students like Baraybar, the message of bat conservation is spreading throughout Peru.
If you want to help support a graduate student project (or for more information about how to apply for a small grant), please contact: Scholarship Awards Committee, BCI, P.O. Box 162603, Austin, TX 78716.
Research Reveals Key Ecological Role of Curaçao's Nectar Bats
Like the Peruvian long-nosed bat, there is little information on the nectar-feeding bats that inhabit Curaçao, one of the Netherlands Antilles islands just off the coast of Venezuela. But with funding assistance from the BCI Student Research Program, Sophie Petit, a recent Ph.D. recipient from the University of Miami, has made some important findings about the role these bats play in supporting the island's cacti.
Petit's research focused on the relationship between two species of bats--the lesser long-nosed bat (Leptonycteris curasoae) and the long-tongued bat (Glossophaga longirostris)--and two species of Curaçao's columnar cacti--kadushi (Subpilocereus repandus) and datu (Stenocereus griseus). Kadushi and datu are vital food resources in Curaçao because they produce enormous quantities of flowers and fruits, particularly during the dry season when resources are scarce. Birds and many other animals rely heavily on them. Unlike cacti in the Andean region of Catherine Sahley's research, these two species cannot self-pollinate and therefore cannot produce fruit without Curaçao's animal pollinators.
Bat populations on the island now constitute only a small fraction of past numbers; early naturalists' accounts and extensive roost stains on cave ceilings indicate much larger original populations. Curaçao's bats have suffered from loss of habitat and human disturbance as the building of a water purification plant has brought development and many more people to the island. Bat censuses in 1992 and 1993 found all of the island's species to be frighteningly sparse. Long-tongued bats were the most abundant, with a count of only 2,000, and lesser long-nosed bats numbered 800-1000, all of which were found in just two caves.
Petit conducted several experiments to determine how important lesser long-nosed bats and long-tongued bats are in pollinating Curaçao's cacti. In her first experiment, she controlled access to the cacti during different times of the day and night to differentiate between pollinators. When bats were excluded from the datu flowers, which close at sunrise, the datu did not produce a single fruit. As for the kadushi flowers, which stay open into the morning hours, only about 10 percent were pollinated, apparently by hummingbirds. Moths were rare and not very effective pollinators. Thus bats appeared to be responsible for the large majority of the fruit produced by both datu and kadushi.
Petit then examined nectar production in the cacti and demonstrated that it coincided with the schedule of bat visitation. The next question was whether the two bat species differed in their effectiveness as cactus pollinators. Would the disappearance of either species alone affect pollination? Petit photographed which bats visited which flowers, then used the number of fruits produced and the number of seeds per fruit to evaluate pollination effectiveness. She determined that long-tongued bats seemed more effective in pollinating datu and lesser long-nosed bats more effective in pollinating kadushi. Her conclusion: the number and diversity of Curaçao's bat species are likely to affect the successful pollination of each cactus species. Consequently, the status of long-tongued and lesser long-nosed bat populations will likely affect the entire ecosystem supported by Curaçao's columnar cacti.
Lastly, Petit wanted to measure the interdependence of the bats and cacti. To determine the extent to which the bats relied upon the kadushi and datu cacti, she collected pollen and fecal samples to analyze their diet. Approximately 85-90 percent of the diet samples contained pollen and/or seeds, demonstrating a heavy reliance on cacti as a food source. Petit also noted that the lactation period of nectar-feeding bats occurs during the peak of the cacti flowering season. The availability of blooms is especially important for the bats because lactation requires extra large amounts of energy. She was left with little doubt that the bats and the cacti are critically important to one another and are probably co-evolving.
Knowing how heavily the bats rely on the cacti, Petit surveyed the population of Curaçao's columnar cacti by taking aerial photographs. She then calculated how many cacti are needed to sustain a given number of bats, concluding that roughly two and a half acres of cactus land is required to support one lesser long-nosed bat. She was not surprised to find from her estimates that the number of cacti is currently limiting bat populations on Curaçao during July and August.
Fearing for the bats' survival, Petit took time whenever she could to share what she was learning about the value of the bats with the Curaçaon public. She gave presentations to school groups as well as adults, many of whom had never been exposed to conservation or environmental concerns. She also wrote newspaper articles explaining why the bats were threatened and emphasizing the need for protection of bats, caves, and cacti.
Petit's work helped focus Curaçaons' attention on the bats for the first time, leading to two positive developments. The manager of Christoffel Park, a 4,450-acre preserve, is now working to acquire several key caves to preserve them as bat roosting sites. And a list of the island's bat species was submitted to officials in charge of new conservation legislation for the Netherlands Antilles, which could ultimately result in official protection for certain species.
After two seasons of field work on the island in 1992 and 1993, Sophie Petit defended her thesis on Curaçao's bat-cactus mutualism in November 1994 and received her Ph.D. last May from the University of Miami.
Three years ago, all the bats on Curaçao could have disappeared without anyone even noticing. Today, there is not only research to validate the bats' value to the island, but also a growing number of concerned residents.
The author extracts nectar from a cactus blossom with a syringe. The amount of nectar produced and the cycle of nectar production reveal much about who a plant's intended pollinators are. Bat flowers produce copious nectar at night, moth flowers much less at night, and hummingbird flowers more by day.
The Peruvian long-nosed bat has a longer muzzle than most other nectar-feeding bats. It has been found only in Peru, and remaining colonies are known to live only in abandoned mines.
The Weberbauer cactus is the only plant species in the author's study area that produces both flowers and fleshy fruits year-round, making it an exceptionally valuable food resource for wildlife.
At the market in Arequipa, many booths feature dead Peruvian long-nosed bats, shown here hanging from the ceiling, on the counter, and proudly displayed by a vendor for the author. On average, vendors sell 5-10 bats a week (a total of about 2,500 a year at this one market) for the equivalent of $5.00 each. Locals pay this costly sum because they believe the bats have medicinal value. While they waste their money, the local bat populations and an entire ecosystem are seriously jeopardized.
Sophie Petit studies a kadushi cactus not far from a Curaçao dance club. Her research was complicated by the club chef's practice of chopping pieces from this cactus for use in a favorite local dish, sopi di kadushi (kadushi soup).
Part of Sophie Petit's research involved taking photos throughout the night to determine which bats were pollinating which cacti. The difference in the tail membranes of the bats pictured here shows one of the ways Petit could identify different species. On the left is a long-tongued bat at a datu flower; on the right, a lesser long-nosed bat at a kadushi flower.