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Daos en el ala de tres especies de murcilagos que se alimentan de nctar (Glossophaginae) del bosque montano bajo muy hmedo en Costa Rica
Wing damage in three nectar-feeding bat species (Glossophaginae) of lower montane wet forest in Costa Rica
Little is known about tropical bats and the damage that collects on their wing membranes over time. Likewise, it is not known whether species or gender differ in the number of scars and tears on wings. This study analyzed the wing damage of three nectar-feeding bats and found that while overall wing damage was not significantly different between gender and species, specific areas of the wing membrane were statistically different. Females generally had higher rates of wing damage to the dactylopatagium major than males (two-way ANOVA, F = 4.21, p = 0.04). Another significant difference involved pregnancy; pregnant females had a higher average number of scars on the plagiopatagium than non-pregnant females (two-way ANOVA, F = 4.21, p = 0.05). As a result of this study, it has become apparent that further research is needed to understand why and how these significant differences occur.
Esta investigacin analiz los daos del ala de tres especies de murcilagos que se alimentan de polen y nctar y encontr que los daos del ala en general no fueron significativamente diferentes entre gnero y especie, pero las reas especficas de la membrana del ala eran estadsticamente diferentes.
Text in English.
Bats--Costa Rica--Puntarenas--Monteverde Zone
Murcilagos--Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology 2008
Wing damage (Bats)
Ecologa Tropical 2008
Daos en el ala (Murcilagos)
t Monteverde Institute : Tropical Ecology
Wing Damage in Three Nectar-feeding Bat Species (Glossophaginae) of Lower Montane Wet Forest in Costa Rica Amanda Nosal Department of Fisheries, Wildlife, and Conservation University of Minnesota Â– Twin Cities ABSTRACT Little is known about tropical bats and the damage that collects on their wing membranes over time. Likewise, it is not known whether speci es or gender differ in the number of scars and tears on wings. This study analyzed the wing damage of three nectar-feeding bats and found that while overall wing damage was n ot significantly different between gender and species, specific areas of the wing memb rane were statistically different. Females generally had higher rates of wing damage t o the dactylopatagium major than males (two-way ANOVA, F = 4.21, p = 0.04). Another significant difference involved pregnancy; pregnant females had a higher average nu mber of scars on the plagiopatagium than non-pregnant females (two-way ANOVA, F = 4.21, p = 0.05). As a result of this study, it has become apparent that further research is needed to understand why and how these significant differences occur. RESUMEN No hay mucha informacin sobre los murcilagos trop icales y el dao en la membrana de sus alas con el tiempo. Adems, no hay mucha infor macin sobre las diferencias en el dao del ala entre las especies y el sexo. Esta in vestigacin analiz el dao del ala, las cicatrices y los desgarros, de tres especies de mur cilagos que se alimentan de polen y nctar. El dao del ala total no tuvo una diferenc ia significativa entre species y el sexo, pero partes especficas de la membrana del ala tuvi eron diferencias estadsticas. Generalmente, las hembras tuvieron ms daos en el quiropatagio que los machos (ANOVA de dos vas, F = 4.21, p = 0.04). Otra dife rencia incluy el embarazo; las hembras embarazadas tuvieron ms daos en el plagio patagio que las hembras que no estaban embarazadas (ANOVA de dos vas, F = 4.21, p = 0.05). Como consecuencia de esta investigacin, es obvio que ms investigacione s son necesarias para entender como y por qu estas diferencias significativas occurieron INTRODUCTION In response to the high-energy solar input and cons equent resources in the tropics, a unique nectar-feeding guild of bats has evolved. A ll flower-visiting bats are members of the subfamily Glossophaginae, which translates from Greek to mean Â“those that feed with their tonguesÂ” (Wainwright 2007). Indeed, the nect ar-feeding bats have long, extensible tongues with bristles on the tip that help to extra ct nectar. Another defining characteristic of Glossophaginae species are short but wide wings for hovering (Wainwright 2007).
While other nectar-feeders, such as birds, utilize feathers for flight, the bat wing is something entirely different. To give structure to the wing membrane, known as the patagium, the forelimb and fingers are extremely el ongated (Altringham 1996). The thumb is a claw that can be used to hold on to surr oundings or a small piece of food. The membrane is constructed of muscle, nerves, and bloo d vessels sandwiched between two layers of skin (Llorar and Schmidt-French 1998). T he blood vessels in the membrane not only transport oxygen, but assist with thermoregula tion. A bat can dissipate heat through its wings and also can completely shut off blood fl ow to the wings via shunts in the blood vessels (Llorar and Schmidt-French 1998). Without flight, a bat cannot feed and hence wing da mage is a sizeable threat to all members in the Order Chiroptera. Glossophaginae ba ts face multiple dangers to their wing health including predation, cluttered and haza rdous surroundings, man-made structures, and even their age. Bats in the tropic s face predation from a number of raptors, including the Bat Falcon ( falco rufigularis ), the Barn Owl ( Tyto alba ), and the Great Potoo ( Nyctibius grandis ) (Chacn-Madrigal and Barrantes 2004). Nectar-fee ding bats have somewhat poor echolocation abilities, due to their small noseleaves and ears, and thus cannot detect sharp objects, such as a pla ntÂ’s thorns, very well (Llorar and Schmidt-French 1998 and R. LaVal, 2008, pers. comm) Bats also have high rates of accidents with barbed-wire fences. The effects of age also can have an impact on wing damage. Juveniles are amateurs at flight and as su ch are very clumsy and thus more prone to accidents (Gelli et al. 2004). The old an d pregnant are can be very awkward in flight as well (R. LaVal, 2008, pers. comm). With such risks as predation and thorny collisions some extant of wing damage is inevitable. In most cases, the damage to the wing membrane is a small puncture wound and can take between six to eight weeks to heal (Ll orar and Schmidt-French 1998). If the hole is small, the bats can still fly and feed, and given time the scar will disappear completely (R. LaVal, 2008, pers. comm.). However, holes too large will ground a bat and it is likely to starve to death. Tears, especi ally to the outer edges of the wing membrane, can drastically affect flight and may be irreparable. Even if large holes and tears heal, the amount of scarring left behind can have long-term effects on the batÂ’s aerodynamics during flight. The purpose of this study is to examine the wing da mage in a sample of bats in the nectar-feeding guild. The aim of this study is to identify relationships between the amount of wing damage, species, and gender. Wing d amage is defined as any visible scars, punctures, and tears. The hypothesis of thi s study assumes that the factors of gender and species have an affect on an individualÂ’ s wing damage. I predict that amount of damage to the wing will be the same for all Glos sophaginae species but different for male and females. The species will have no signifi cant difference in wing damage because they lead such similar lives (e.g. foraging behavior and social structures). Yet, a difference between the sexes is expected because fe males can have differing diets from males and the added weight of pregnancy may alter t heir ability to avoid predation and hazardous objects. One study focusing of the repro duction of a specific Glossophaginae species, Glossophaga commissarisi, noted that females ate a far greater amount of ins ects than males (Tschapka 2005). The differences in for aging between males and females could put the females at a higher risk of wing dama ge because the females are chasing after their food.
Methods STUDY SITES This study was conducted in a hummingbird garden in Selvatura Park in Monteverde, Costa Rica, for six nights between July 24th and July 31st, 2008. Starting at approximately 6:20 p.m. mist nets were erected and remained open until 9:00 p.m. Usually, a 12 m long mist net was used, although tw ice a 5 m mist net was also set up. Every twenty minutes from the time the nets were up I would inspect the nets and collect the individual bats in cloth bags. In an attempt t o attract more bats near during the last three nights, I filled the birdfeeders with sugar w ater. The position of the nets also changed every two nights so that bats would not lea rn to avoid them. Once the bats were caught, their wings were prompt ly inspected. By placing a flashlight underneath the wing, I was able to count the scars and current punctures in five parts of the wing membrane Â– the propatagium, plagi opatagium, dactylopatagium major, dactylopatagium medius, and the dactylopatagium min or (fig. 1). A scar is identifiable under the light because it appears as a pinkish dis coloration, usually with a somewhat circular shape although some more linear tear scars were found. To ensure that a bat was not recorded twice, a small chunk of hair was remov ed from their backs. Gender and species was recorded and a note was made if a femal e was visibly pregnant. In order to test for possible differences in wing damage and ge nder and species, as well as between pregnant and non-pregnant females, two-way ANOVA te sts were used. RESULTS In total, sixty-nine bats were mist-netted. The po pulation was composed of three species of the nectar-feeding guild: Anoura geoffroyi (n = 33), Anoura cultrata (n = 13), and Glossophaga commissarisi (n = 23). The A. geoffroyi sample had twelve males and twenty females, the A. cultrata sample had four males and nine females, and the G. commissarisi sample had fifteen males and nine females. The A. geoffroyi and A. cultrata sample had a combination of thirteen visibly pregn ant females ( A. geoffroyi n = 9, A. cultrata n = 4). No pregnant females were recorded for G. commissarisi Fourteen two-way ANOVA tests were run and three of them had significant results (table 1). Although there was no differenc e in the number of total scars between gender and species, a specific part of the membrane did have significant differences. The dactylopatagium major data showed significant diffe rences in gender and gender x species effects. From the corresponding graphs (fi gures 2 and 3) it can be generalized that females have a higher number of scars on their dactylopatagium majors and overall A. cultrata females had the highest number of scars on the dac tylopatagium major. The last three tests reveal significant differences con cerning the pregnancy status effect. It was discovered that non-pregnant females had higher averages of scars on the propatagium than pregnant females (figure 4). Howe ver, it was the pregnant females that had the higher averages of scars on plagiopatagium (figure 5). Lastly, a significant difference was found when the effect of pregnancy x species was tested; non-pregnant A. cultrata females had the highest average of scars on the pr opatagium (figure 6).
DISCUSSION The results of this study had a combination of data that both agreed and disagreed with the predictions. The first prediction, that wing d amage would not differ among the species, was supported. The second prediction anti cipated a significant difference between wing damage for males and females, and spec ifically that females would have higher wing damage. While this was not supported f rom evidence on overall wing damage, females had a significantly higher average number of scars on the dactylopatagium major. There are a number of plausible reasons why the ave rage number of scars on the dactylopatagium major was higher for females than m ales. The first involves the differences in lifestyles. Females hunt for insect s more than males and that may present more hazards than simply foraging for flowers and f ruits. Most bat species live in colonies, but the size and sex composition of these colonies varies between breeding seasons. For example, A. geoffroyi individuals reside either in reproductive or matern ity colonies, depending on the time of year. In the re productive colony many males are present, but after awhile they migrate and leave th e females and their young in a maternity colony (Galindo et al. 2000). Maternity colonies consist of many individuals packed tightly together. Perhaps some scars are ca used accidentally, if one bat scratches another as it attempts to move through the mass of the colony. When mothers with pups fly, the small pups cling to the chest of their mot hers; perhaps pups scratch or puncture the inside wing of its mother when moving. However that would imply that the pregnant mothers analyzed in this study had previously been mothers, a fact that the study could not determine. Lastly, scars may arise if bats are physically aggressive to fellow colony members (R. LaVal, pers. comm.), which few biologis ts have ever observed. Only one or two species of bats have been observed attacking ot her their own colony members and nectar-feeding bats were not one of them. The effect of pregnancy status revealed that the av erage number of scars on the propatagium was higher for non-pregnant females, wh ile the average number of scars on the plagiopatagium was higher for pregnant females. This fact is difficult to explain; not enough is known about bat behavior to account for i t. Age should be taken into account in this situation. This study did not record the a ges of the studied bats and perhaps pregnant females have more wing damage because they are simply older than the nonpregnant, supposedly juvenile females. I have a sm all theory that could explain why the not pregnant females higher averages of wing damage to the propatagium. If we assume that they are indeed younger, perhaps they have mor e damage on the propatagium because they are inexperienced flyers and do not ye t comprehend the consequences of damage to this specific part of the wing membrane. The propatagium is part of the leading edge wing flap and enough damage could dras tically alter the way the air passes above and under the wing during flight (Altringham 1996). As a soon to be mother and supposedly older female, the pregnant bats may take more precautions to ensure nothing alters their aerodynamic in flight and thus jeopard izes the survival of their pups. As a consequence of this study, a number of new que stions have been unearthed. Results of wing damage lead to questions about wher e the scars originate. Observational studies on this are sorely needed. Furthermore, if females tend to have a higher average number of wing scars, does that correlate with high er mortality? How does the wing damage of nectar-feeding bats compare with fruit-fe eding and insect-feeding bat species?
Does the area of the membrane section relate to the number of scars present? This study has merely hinted at the intricate web of interacti ons bats participate in and the resulting wing damage that can be obtained. ACKNOWLEDGMENTS I canÂ’t extend enough thanks to everyone who assist ed me as I dived into my first independent research project. First of all, IÂ’m gr ateful to Selvatura for allowing me to conduct my study on their property. IÂ’d like to sa y Â“thank youÂ” to Karen Masters for pointing me in the right direction and arranging my research at Selvatura Park. Thank you to Pablo, Kelly LaVal, Arturo, and Uriel for he lping untangle all sixty-nine of the tiny nectar-feeding bats. Thanks to Richard LaVal for taking time out of his schedule to talk batty with me. A million thanks to Raffa and Jason who were always ready to help me get to where I needed to be and even helped me o ut when we got there. And finally, thanks to all the bats (especially the pregnant mam as) who, for the most part, tolerated my disruption of their nightly feeding routine. Al ong with my acknowledgments, I must also include my apologies to the one bat who got ca ught in my net and was discovered by a raccoonÂ… LITERATURE CITED Altringham, J.D. 1996. Bats: Biology and Behaviour. Oxford University Press Inc. New York, New York. pp. 63. Chacn-Madrigal, E. and Gilbert Barrantes. 2004. Bl ue Crowned Motmot ( Momotus momota ) predation on a long-tongued bat (Glossophaginae). Wilson Bulletin 116: 108-110. Galindo, C.G., Campillo, A.C., Mndez, A. S., and J R. Pulido. 2000. Reproductive events and social organization in a colony of Anoura geoff royi (Chiroptera: Phyllostomidae) form a temperate Mexican cave. Act a Zoo. Mex. 80: 51-68 Gelli, D., Vernier, E., and S. Romagnoli. 2004. Juv enile pathologies in European insectivorous bats. Bat Research News 45: 111. LaVal, R.K. and B. Rodrguez-H. 2002. Murcilagos d e Costa Rica Instituto Nacional de Biodiversidad. Santo Domingo de Heredia, Costa Rica pp. 134-157. Llorar, A. and B. Schmidt-French. 1998. Captive Car e and Medical Reference for the Rehabilitation of Insectivorous Bats Bat World. Mineral Wells, Texas. pp. 115119. Tschapka, M. 2005. Reproduction of the bat Glossophaga commissarisi (Phyllostomidae: Glossophaginae) in the Costa Rican forest during fr ugivorous and nectarivorous periods. Biotropica 37: 409-415. Wainwright, M. 2007. The Mammals of Costa Rica: A N atural Field Guide Cornell University Press. Ithaca, New York. pp. 106-110.
Figure 1. The five parts of the wing membrane anal yzed for wing damage in this study. The dactylopatagium brevis was excluded because it was inconspicuous in the majority of the bats studied. nr Figure 2. Male vs. female comparison of scars on t he dactylopatagium major. The graph above reveals that the significant difference calcu lated from the two-way ANOVA test describes how, in general, females have more scars on the dactylopatagium than males. Bars represent standard error. This graph includes all three species studied. QuickTimeÂ™ and a TIFF (PackBits) decompressor are needed to see this picture.
Figure 3. Average number of scars on the dactylopa tagium major. This graph represents the gender differences in the scar number of the da ctylopatagium major. Also noticeable is the trend in which the females of A. cultrata tend to have the highest average of scars on this specific part of the wing membrane. Bars represent standard error. nnnrnnnnr Figure 4. Comparison of scars on the propatagium o f pregnant and non-pregnant females. The non-pregnant females generally had a higher num ber of scars on the propatagium than pregnant females. Data only included females from A. geoffroyi and A. cultrata because it was not the breeding season for G. commissarisi Bars represent standard error. nnr r n rn
nnr n n Figure 5. Comparison of scars of propatagiums of p regnant and non-pregnant females between A. geroffroyi and A. cultrata This graph demonstrates the significant difference of scarring on the propatagium of pregna nt and non-pregnant females but also includes species. Bars represent standard error. nnnrnnnr Figure 6. Comparison on scars on the plagiopatagiu m of pregnant and non-pregnant females. In general, pregnant females had the high er average number of scars. Bars represent standard error.
Table 1.The two-way ANOVA results for the five test s with significant results. Pregnancy status was based on whether or not the fe male was visibly pregnant or not. Section of Wing Membrane Effect DF F Ratio p value Dactylopagatium major Gender 1 4.21 0.04 Gender x Species 2 3.10 0.05 Propatagium Pregnancy Status 1 4.26 0.05 Species x Pregnancy Status 1 6.06 0.02 Plagiopatagium Pregnancy Status 1 4.21 0.05