Jamaican Caving Notes
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August 21-23, 2011
Team: RS Stewart, Yvonne Dzal, Nina Veselka
Notes: RS Stewart
Video (36MB WMV)
Bats provide a fascinating system in which to study the importance of trade-offs in constraining phenotypic evolution. As the only mammals capable of powered flight, bats have been able to exploit novel ecological niches and are one of the most diverse groups of mammals. Their commitment to flight has resulted in highly specialized forelimbs: their arms, wrists and hands have been modified into wings. However, this has limited how bats use their forelimbs for activities other than flight. The consumption of food, for example, is necessary for survival, and many mammals use their arms and hands to collect and handle food items.
In bats, thumbs are the only structures of the forelimbs that do not contribute to supporting the flight surface. Although several studies have confirmed that bats use their wings during feeding, few have provided details on how thumbs are used for food handling. The project is focussed on New World leaf-nosed bats (phyllostomids), which exhibit the greatest diversity of all living mammals (feeding on fruit, insects, frogs, nectar, blood). Dumont, et al. have found that the evolution of fruit consumption in phyllostomids led to high rates of species diversification. Keeping this in mind, the project has two main hypotheses:
Hypotheses: The transition from fruit consumption to insectivory in phyllostomids is correlated with increased thumb use.
Prediction: Frugivorous phyllostomids will use their thumbs more frequently than non-frugivores (since fruit is relatively large and requires more mechanical processing before consumption than do insects).
Hypotheses: There is an evolotionary relationship between thumb size and diet.
Prediction: Fruit bats will have longer thumbs than non-frugivores.
To help test the prediction that frugivores use their thumbs more frequently than non-frugivores to manipulate food, the bats were captured in mist nets, transferred to the field-station, and videoed using infrared light that provided illumination without disturbing the bats. Bats that have a frugivorous diet should use their thumbs more than insectivorous, carnivorous, or omnivorous bats. Frugivores should also exhibit a greater number of thumb movements than as they manipulate food during consumption.
To test the evolutionary relationship betweent thumb size and diet, thumb lengths were measured with calipers.
Now, an account of the field activities.
On Sunday, August 21, we began the fieldwork by trekking to the main entrance of St Clair at about 16:00, and setting up a 3m mist net, set about 5m back from the entrance pit. I had warned them that unlike Windsor Cave, where they hadn't actually gotten many bats in the nets, at St Clair the problem would be the opposite - if they used too long a net, they wouldn't be able to keep up with the numbers caught, and we'd have too many bats hanging in the net for too long. The prediction was accurate, and the 3m net was certainly as much as we could handle during the evening.
The first bat was caught at 18:02, one of the two small Pteronotus, either a macleayii (P.m) or a quadridens (P.q). We wouldn't know until later when it was processed, because the only way of telling the difference is to measure the forelimb - the quadridens are always under 41mm, and the macleayii are over 41mm. The second bat, a Mormoops blainvillii, was caught at 18:05, the third, another P.m or P.q, came at 18:13, and then the numbers began to rapidly increase. The main surge was from between 18:40 and 19:30, during which time we caught somewhere on the order of 100-150 bats. Towards the end, most were simply removed and released, rather than bagged for processing.
The net was taken down at 19:50, after we'd finally removed all of the bats. I did what I could to help with this, but some were too tangled for me to manage, and I had to leave them for Nina or Yvonne. During the first while, I received some rather painful bites, as usual. However, I did seem to improve later on, thanks to Nina's guidance, and was doing pretty good at the end.
Only four species were caught, Pteronotus parnellii (P.p), Pteronotus macleayii, Pteronotus quadridens, and Mormoops blainvillii (M.b). The bats we'd bagged were processed (identified, weighed, sexed, and forearms measured) from 20:00 until about 23:30, and we then hiked back to Pollyground, reaching Marie's at about midnight.
At 21:25, the second bat of the evening was caught - an Artibeus in the river nets. At 22:00, a third bat, another Ariteus, was caught in the net across the track, and that was it for the night. We hung in until about 23:00, then gave up and returned to Marie's with what we had. The night was not too unsuccessful, though - we'd capture only three specimes, but at least they were all phyllostomids.
The next evening, the 23rd, we again ignored the cave and set nets on the approach to the river, and across the river somewhat upstream of the "V" net of the night before. The nets were designated, and located, as such:
N1 - a 5m net about 1/3 of the way through the bushy saddle on the track that leads to the river,
N2 - a 3m net at the same location as the second net on the 22nd, which is about 2/3 of the way through the saddle,
N3 - a 15m net right across the river just upstream of the track.
The first bats, two P.p, were caught in N1 at 18:40. Next was N2 with a P.p at 19:05, a M.b at 19:10, and an A.j at 19:25. Nothing was caught in N3, the river net, until an A.j entered it at about 21:45. I write "about", because all three of us had fallen asleep for a little while on rocks beside the net, and it was 21:45 when the first of us, me, woke back up to find a bat in the net. In our defense, I must note that we'd been out there the two previous nights until midnight, and we were all rather beat. N1 yielded another Pteronotus sp. at 22:00, N2 an A.f at 22:05, and N3 a final two A.j at 23:10.
We'd had plenty of time to process bats as we went along, so it didn't take us long to finish up when the nets came down about 23:30. We hiked back out and reached Marie's about 00:30.
It should be mentioned that although my participation was ending about midnight on the three nights, Nina and Yvonne were up for hours afterwards videoing the frugivores, Artibeus and Ariteus, as they fed in a small enclosure at Marie's.
On Thursday, August 25, we had to make a run into Kingston so that Nina could show her data and specimens to NEPA in order to finish up the paperwork. Once we'd reached there, we were told that it would take several hours to have the permit prepared, and that we also needed to go to Veterinarian Services to clear things through them. Their office was kilometers away, up Old Hope Road, but we had time to kill anyway, so we headed off to take care of it. Now follows the most bizarre encounter with a Jamaican government agency that I've ever had.
It soon became clear that Veterinarian Services did not really care what Nina was doing, and what she had in her pickle jar, since the bats were quite dead, and thusly beyond their purview. Indeed, even if the bats had been alive, they're not exactly livestock, and I doubt they would have been terribly concerned. They did try to ask some pertinent questions, though, such as if NEPA had issued permits. Nina's assurances that all permits were in place adequately satisfied them, and after some pleasantries, and amused smiles on both sides, we left to wend our way back to the NEPA offices. Once there, the final paperwork was received, and we began our drive back to Pollyground, becoming somewhat lost in Kingston as we did so. Fortunately, I eventually spotted the Halfway Tree bus terminal, figured out where we were, and got out of town.
My fieldwork with Nina and Yvonne was now finished, but on Sunday, August 28, I had the pleasure of them joining Christina (wifey) and I for my birthday bashment at Marie's. Being very good sports, they donned little aprons that Christina supplied, and helped her with the cooking. All three looked very cute. Afterwards, an appropriate amount of Red Stripe was consumed, and I assume I had a good time, although my memories of the final hours of the evening are a little vague.
I would like to pass along my great respect for Nina and Yvonne. They are dedicated, committed, and quite happy to pass along their knowledge and techniques to those who collaborate with them, such as myself. I learned a lot, and am very thankful for it.
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