With the start of the winter solstice (southern hemisphere) on the 20 June 2020 (longest night) marked the end of the 2019/20 field season. So, the 21 June 2020 marked the first day of the 2020/21 field season. But bats are still in deep torpor and hibernation due this still being winter. But our passive monitoring equipment allows us to keep track of the bats without need to capture and handle at this critical point during the year. But moving closer towards spring, the days grow longer and nights shorter, the energy received from the sun increases, bringing warmth and productivity to the region. By mid-August temperatures have warmed up and insects (food) are more abundant, bats have had the opportunity to fatten up after a long winter.
The first active sampling for this 2020/21 season took place on the 18 August 2020 at Mamelodi II Cave (Gauteng Province, South Africa), where a total of 52 Natal Long-fingered Bats (Miniopterus natalensis) were captured, of which 26 were measured, and 20 implanted with radio-frequency identification (RFID) tags. While three previously RFID tagged individuals were recaptured, with an average of 290 days of being tagged. One of the female bats had been previously recaptured 138 km away at the Madimatle Cave (Limpopo Province, South Africa), 13 days after being originally tagged (during the 2019/20 field season). This shows that there is a two-way movement between the Mamelodi II and Madimatle Caves.
25th August 2020, back at Mamelodi II Cave, where a total of 45 Natal Long-fingered Bats were captured. Twenty seven were measured and 21 RFID tagged. Five individuals were recaptured, with one of the recaptured individuals being tagged on the earlier trip (18 August 2020). Excluding this individual, the average number of days tagged of the remaining four individuals was 348 days. One female of these four was originally tagged at Madimatle Cave 631 days (1.7 years) earlier. On 8-9 September the AfricanBats NPC field team was joined by a two person film crew at Mamelodi II Cave, who were present to film our work (see “50/50 filming event”).
The 8th September was planned fieldwork, which progressed as per normal, where 59 Natal Long-fingered Bats were caught. Forty individuals measured, and 38 RFID tagged. A single individual, which was recaptured had been tagged at this same cave 573 days previously. During the unplanned field event (see “50/50 filming event" ) on the 9th September – we do not want to create excessive disturbance by repeated entering of the cave – a mockup field event was set up for educational purposes, to allow the filming of field procedures and the bats in a controlled environment. Only 15 individuals were captured and measured, and 10 RFID tagged. None of these bats had been captured before.
6th October back at Mamelodi II, 62 Natal Long-fingered Bats were processed. No bats were RFID tagged, due to lack of funding to secure stock and restrictions on travel for individuals to bring us more tags and needles. Therefore, for the rest of this field season no bats were tagged. However, two previously tagged Natal Long-fingered Bat were recaptured, with one having been tagged during this field season (37 days before) and the other 610 days before. A single male Tricolored Bat (Myotis tricolor) was recaptured 366 days after being tagged at Mamelodi II Cave. This recapture at the same site and similar time of the year, suggests that this species may also have a predictable migration pattern. But further monitoring at this cave over future years will be needed to test if this is just a random coincidence or an actual predictable migration event.
20th October, 55 Natal Long-fingered Bats were processed at Mamelodi II Cave. Three RFID tagged bats were recaptured, with two being tagged this season (42 days previously) and a female that was originally tagged at Madimatle Cave (132 km away) 701 days (1.94 years) before.
3rd November again at Mamelodi II where 83 Natal Long-fingered Bats were measured. One RFID recaptured individual, which was tagged 55 days before. On the 10th November the Mamelodi II Cave was visited, but no bats were captured as the vast numbers of individuals were no longer present. Only a few Natal Long-fingered and Horseshoe Bats (Rhinolophus sp.) were seen flying within the cave.
While the Biomark cable reader system has been deployed (almost constantly) at the Mamelodi II Cave since 16 December 2019, it was removed between 28 November – 8 December 2020, and 21 - 23 January when the cable reader was deployed at the entrance to the Madimatle Cave. A number of RFID tagged Miniopterus were detected. The most important discovery being two individuals who were tagged during our first tagging event in December 2017 (see "First PIT tagging session" and Pretorius (2018)). The two Natal Long-fingered Bats were detected in December 2019, 1086 days (2.9 years) and January 2021, 1138 days (3.1 years) after being tagged.
The Mamelodi II Cave was visited on the 11 December 2020, 8 January 2020, 25 January 2021, 11 February 2021 – where 10 or less bats were observed, and no bats captured. On the 19th February 2021 a few bats (less than 50) were seen, and three Natal Long-fingered Bats caught. On 23rd February 2021 the numbers of bats present in Mamelodii II Cave were still low. Three Natal Long-fingered bats and two Geoffroy's Horseshoe Bats (Rhinolophus clivosus) were caught. On 4th March bat numbers increasing and 30 Natal Long-fingered Bats were caught, including one recapture (177 days after RFID tagged). The population numbers were clearly on the increase on 11th March 2021, when the bats were also very active. Twenty four Natal Long-fingered Bats were processed. The cave was visited on the 16th March 2021 where estimated numbers were similar to 11th March, but no attempt at capture was made. On the 23rd March 2021 estimated numbers were like those during the earlier two visits. Fifty Natal Long-fingered Bats were captured and processed. With two being recaptures, one from this field season (217 days previously) and the other 769 days (2.1 years) of being RFID tagged.
On 13th April 2021, 40 Natal Long-fingered Bats and four Geoffroy's Horseshoe Bats were caught and processed. Two of the Natal Long-fingered Bats were recaptures, both tagged on the same trip 217 days before.
During the previous field season (2019/20), we were able to sample until late May. With a predicted cold front, the next planned sampling event for April was postponed. Expecting that there would be a warm spell before winter sets in around late May/early July. Unfortunately, this did not occur and winter this year came early this season. With the onset of winter (one of the most vulnerable periods for disturbance to these cave bats), active sampling was halted. But passive monitoring equipment – cable reader system and bat detector, will continue to supply information on the bat activity over winter. Sampling for the 2021/22 field season is expected to start mid-September 2021.
The above fieldwork could not have been made possible with the support of active AfricanBats NPC volunteers: Miss Mengjing Wei, Mr. Steven Tucker, Mrs. Margaret Bartkowiak and Miss Nardia Hansa, Drs. Teresa Kearney and Mark Keith. Victor Van Cakenberghe who contribution to data management, that allows for quick summaries of data collected. To landowners Gordon and Cindy Hooper (Mamelodi II Cave) and Nchakha Moli and Thabile Mlaba (Motjoli Real Estate) for giving us permission and the support to undertake this work at the caves that they are the primary stewards.
During the 2020/21 field season a total of 89 Natal Long-fingered Bats were implanted with RFID tags. Thanks to the Rufford Foundation for funding the RFID tags. As more volunteers are trained in correct field handling skills and mastering the skills. The field teams are expected to become larger, where additional equipment will be needed. Some volunteers have already gained experience to take part in the implantation of RFID tags. Therefore, those who would wish to support this project please consider donating to AfricanBats NPC.