IZW - Leibniz Institute for Zoo and Wildlife Research

Current Highlights

Artificial bat roosts could re-seed the tropics
Luring bats to new homes in deforested areas could help regeneration.

Matt Kaplan

Conservationists are learning to harness a new weapon in the fight against deforestation: bats. Bats have a crucial role in dispersing seeds from local plants in the neotropics — an ecological zone that includes South and Central America. Now, researchers have found that they can attract bats to deforested areas using artificial bat roosts, where the bats set up home and defecate the seeds of recently eaten fruit in their new neighbourhood. Deforested areas of the neotropics are notoriously difficult to regenerate. After trees are chopped down so land can be used for plantations and cattle pastures, the resulting nutrient-poor soil is often unable to produce plants of any significant value, and so the land is abandoned. With no overhead cover and few food sources, abandoned plantations and pastures offer fruit-eating animals such as bats little reason to leave the safety of their forest home and defecate the seeds where they are needed most. This has led to extensive research into how seed distributors can be lured into open areas... naturenews

Original publication in Conservation Biology

Contact:
Dr. Detlev Kelm, kelm@izw-berlin.de, +49 30 5168 513

Incest-avoiding females cause males to leave

Animals generally avoid inbreeding because it is genetically hazardous. They can either do this by moving away from home or, like humans, by learning who their relatives are and not mating with them. In most mammals, the young males move away and the females stay, resulting in a low level of inbreeding. But why is it the males that move away, given that the females invest much more in raising their offspring and should therefore have a greater interest in avoiding inbreeding?

Research on spotted hyenas published in Nature this week by an international team of scientists from the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, Germany, and the University of Sheffield, UK, now shows that the reason most males move from their natal group is because of female mate-choice - the rules females use when choosing which of many male group members will sire their offspring. Young females prefer to mate with "new arrivals" in a group - males born into the group or males that immigrated into the group after the female was born - because by doing so they avoid breeding with their father and their older brothers. Females are unlikely to know who their father is because - like most male mammals - male hyenas do not contribute to the rearing of their offspring and females mate promiscuously.

Older females also apply this rule and in addition prefer males that have built friendly relationships with them for several years. These age-related mate preferences of females (assortative mating) influence where males choose to initiate their reproductive careers because ultimately they determine a male’s reproductive success. The results of this study demonstrate that males mostly start their reproductive careers in groups with the highest number of young females and that the males that choose groups containing the highest number of young females sire the highest number of offspring in the long term. "Long-lived males that selected the correct group at the start of their reproductive career had access to a high number of females for many years and sired far more offspring than other males", says Dr Oliver Höner from the IZW. Most males disperse because a higher number of young females usually occurs elsewhere, rather than in the group in which the male was raised. Dr Höner adds: "The results of the study were only possible because we could monitor the decision by males on where to start their reproductive career in all eight resident hyena groups on the floor of the Ngorongoro Crater and we could genetically determine paternity for most offspring produced in a 10-year monitoring period."

This is the first time it has been shown in a mammalian species that the males that respond best to female mate preferences and as a result in most cases move from their natal group do pass on more of their genes to future generations, and that the system is driven by females using very simple rules, which are enough to prevent them from mating incestuously.

Reference:
Höner OP, Wachter B, East ML, Streich WJ, Wilhelm K, Burke T, Hofer H. Female mate-choice drives the evolution of male-biased dispersal in a social mammal. Nature, 16 Aug 2007.

Contact:
Oliver Höner, hoener@izw-berlin.de, +49 30 5168 516

Bat breath reveals the identity of a vampire’s last victim

Vampire bats that live in Latin America have switched to blood meals from cattle instead of from rainforest mammals, ecological physiologists from the Leibniz Institute for Zoo and Wildlife Research, Berlin, the Freie Universität Berlin, the Humboldt Universität zu Berlin and the University of Aberdeen report in the Journal of Comparative Physiology B online. They say that the conversion of rainforests ecosystems into livestock producing farmland resulted in the expansion of vampire bat populations in Latin America.

Farmers are observing vampire bats satisfying their need for blood by attacking cattle instead of wild mammals. To document this change in behaviour, Dr Christian Voigt and colleagues analysed the stable carbon isotope ratio of exhaled CO2 in vampire bats. They fed captive vampires blood that was labelled with the stable (non-radioactive) isotope carbon-13 and then monitored the time period between the blood meal and the appearance of labelled carbon atoms in the exhaled breath. "Vampire bats used the freshly ingested blood very fast to fuel their metabolism; after less than an hour the stable carbon isotope signature of the vampires’ exhaled breath was similar to that of their latest diet" Dr Voigt states.

Then the researchers collected breath of free-ranging vampire bats in Costa Rica and analysed its stable carbon isotope signature. "The potential victims of vampires in Costa Rica are either cattle or rainforest mammals such as tapirs and peccaries. These two groups of animals feed on isotopically distinct plants which are grasses in the case of cattle and herbs or shrubs in the case of rainforest mammals. Therefore, we expected that the stable carbon isotope signature in bat breath would change according to their diet" Dr Voigt continues. The vampires’ breath clearly indicated that their last blood meal almost always originated from cattle, although rainforest mammals were also present.

The authors argue that the vampire bats do not necessarily prefer cattle blood, but that cattle are much easier to find for vampires than rainforest mammals. Cattle are held fenced-in on open pastures, whereas rainforest mammals roam in dense vegetation. Converting rainforests into pasture has a large impact on many native mammals of Latin America, usually not to the benefit of the original mammal fauna.

Vampire bats live only in Central and South America and weigh 30 - 40 g. Vampires share food among unrelated group members, a behaviour known as reciprocal altruism, which vampire bats have in common with humans.   

Reference:
C C Voigt, P Grasse, K Rex, S K Hetz and J R Speakman (2007). Bat breath reveals metabolic substrate use in free-ranging vampires. Journal of Comparative Physiology B, DOI : 10.1007/s00360-007-0194-z is published online on 16 August 2007.

Contact:
Dr Christian Voigt, Leibniz Institute for Zoo and Wildlife Research (IZW), Berlin, tel: +49 30 5168 517, email: voigt@izw-berlin.de

Sugar rush. Eat all the sugar you want without gaining weight? What sounds like a delightful diet is no picnic for the nectar-feeding bat.

According to an upcoming study in Functional Ecology, the bat burns sugar faster than any other mammal--and about two or three times faster than humans--but because of its low body fat, the animal risks death if it doesn't eat every 12 hours. The bat is one of the few mammals with a purely sugar diet, making it a promising model organism for studying insulin metabolism and diabetes, say the authors. (Photo: Merlin D. Tuttle, Bat Conservation International)

Antelope feared extinct is rediscovered in Angola

Pitra C, VazPinto P, O´Keeffe BWJ, Willows-Munro S, Jansen van Vuuren B, Robinson TJ (2006) DNA-led rediscovery of the giant sable antelope in Angola. Eur. J. Wildl. Res. (DOI 10.1007/s10344-00-0026-y


Of all the animals to lose, the giant sable antelope might seem be the most embarrassing. The mammal, which only lives in Angola and has horns that can grow to 1.5 metres long, was feared extinct. But an international team of scientists from the Leibniz-Institute for Zoo and Wildlife Research in Berlin, the Universidade Católica de Angola, the Shikar Club, England, and the University of Stellenbosch, South Africa have shown that the animal is hardier than anyone thought, having survived 30 years of civil war and unrest in its native country. The team examined pictures from camera traps and genetic material from droppings and compared it with DNA-samples that came from museum specimens. "Our findings are of great importance for conservation. The giant sable antelope is not only the national symbol of Angola, it is also a flagship species for conservation." The giant sable antelope was discovered in 1914 and was last sighted in Angola in 1982. Since then there had been rumours but no hard evidence that the animal still existed in Angola. When the scientists confirmed that the DNA found in the dung they had collected matched the DNA of a giant sable they set up cameras to gather more direct evidence. These captured images of the giant sables regularly visiting parts of the Luando Integral Nature Reserve and the Cangandala National Park. One female pictured was clearly pregnant.