Rediscovery of the “missing” Pinatubo volcano mouse

In June 1

991, Pinatubo, a volcanic peak on the Philippine island of Luzon, literally blew up its peak. It was the second most powerful volcanic eruption of the 20th century, ten times stronger than Mount St. Helens, and the consequences were devastating. Lava and ash spewed into the environment in the Zambales Mountains, forming layers up to 600 feet thick in the valleys. After the eruption, heavy typhoons and monsoon rains caused landslides and ash that lasted for many months. Eight hundred people lost their lives, and the lush forests that covered the mountain before the eruption were destroyed or severely damaged. In recent years, scientists have returned to the region to study surviving mammal populations and in a new article in Philippine Journal of Science, the team announced the rediscovery of a species of mice it had long feared would disappear.

“When Pinatubo blew up, probably the last thing anyone thought was that small species of mice were thought to live only on this one mountain and as a result may have disappeared. What we learned later really blew us away, “says Larry Heaney, curator of the Negaunee for mammals at the Chicago Field Museum and one of the newspaper’s authors.

In early 2011 and again in 2012, twenty years after the eruption, researcher at the Danilo (Danny) Ballet Field Museum went to the mountains. Pinatubo for studying the fauna of mammals. For several months, Ballet and his team of field assistants (including local Aeta men) studied mammals in the mountains, from the bottom to near the top, where the forest was devastated by the eruption.

“Most of our field work in Luzon and elsewhere in the Philippines has been in natural wooded habitats, where mammals are most common,” said Eric Ricart, a vertebrate curator at the Utah Museum of Natural History and lead author of the paper. but Danny couldn’t miss an opportunity to see how the mammals handled Pinatubo Peak. “

There have been no mammalian studies of Mt. Pinatubo before the eruption. However, specimens stored in the National Museum of Natural History of the United States provide some records of lower elevations around the mountain. “Most of these early records are of common bat species collected in the 1950s,” says Heaney, “but one specimen was particularly intriguing – a small rodent that became the typical specimen and the only example of a new species described. in 1962 as Apomys sacobianus, the volcanic mouse Pinatubo. “

The conditions on Mount Pinatubo were very harsh and the exploration of the Balete team was both exhausting and dangerous. Even after 20 years, evidence of the eruption was everywhere. The landscape was very unstable due to the constantly eroding deposits of ash and lahar, which made working in the steep terrain dangerous. In addition, it significantly slows down the process of plant succession. The vegetation was a sparse mixture of native and non-native plants, dense grasslands (including bamboo), shrubs, low-growing vines and few trees – all characteristic of the habitat of the second growth at an early stage. It was far from the rainforest that covered the mountain before the eruption.

Field studies of small non-flying mammals elsewhere in Luzon have revealed that the old forests contain a wide variety of native species and few, if any, non-native “rat” species. But in severely disturbed second-growth habitats, especially in areas close to crops, the opposite is true for non-native rats at most and there are only a few hardy native species. “We thought working on Pinatubo would confirm this common pattern, so we expected to see a little if there were any native species,” says Ricart.

A specific motivation for the Pinatubo study was to discover the fate of Apomys sacobianus, the Pinatubo volcano mouse. “After the Pinatubo eruption, we looked for this mouse on other peaks in the Zambales Mountains, but we couldn’t find it,” notes Heaney, “which suggests a very limited geographical distribution of the species. We thought that the volcano may be the only place where a mouse lived. “And based on expectations from islands elsewhere, it seemed possible at the time that the species was lost due to the eruption.

However, the Pinatubo study yielded some very surprising results – a total of 17 species were documented, including eight bats, seven rodents (five native and two non-native species) and even two large mammals (wild pigs and deer). Contrary to expectations, non-native rats were not common at all and were limited to areas near Aeta farmland, where such agricultural pests are often most prevalent. Despite the fact that all the study areas maintained sparse, second-growth shrub vegetation rather than forest, native rodents were abundant everywhere.

Most surprising of all, the most common species predominant was the volcanic mouse Apomys sacobianus. This species is far from being destroyed by the eruption, and this species thrives in this highly disturbed landscape, along with other native species that also have a high tolerance for disturbance. We have known for some time that many small mammals in the Philippines can tolerate habitat disturbance, both natural and man-made, ”says Ricart,“ but most of them are geographically widespread rather than locally endemic species that are usually considered by conservation biologists to be highly vulnerable. “

As Mt. Pinatubo is recovering from the damage caused by the eruption, the forests will return and other mammal species will settle. “Mount Pinatubo could be a great place to set up a long-term project to monitor habitat restoration and reunite the community after an eruption,” says Ricart, “such information would be useful in efforts to restore many areas deforested.”

After completing Mt. Studying Pinatubo mammals, Danny Ballet returned to the Field Museum, where he organized samples and data from the study, made a few early notes for possible publication, and then set them aside to finish later. After he died suddenly in 2017 at the age of 56, Ricart and Heaney say they took and completed the study in honor of Ballet, who is now recognized as one of the most important figures in Philippine biodiversity science because of its extensive his research contributions, mentoring younger colleagues and promoting the enjoyment of nature throughout the Philippines.

“Knowing that a species that was once considered vulnerable, even afraid of extinction, is actually thriving is the best homage to Danny we can imagine,” Heaney added.

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More information:
Eric A. Rickart et al. Mammals from Mt. Pinatubo, Luzon Island, Philippines: Exceptional resilience after catastrophic disturbances. Philippine Journal of Science, (2021)