By Charles Mpaka
Blantyre, MALAWI — When Cyclone Idai stormed Mozambique in 2019, researchers at Gorongosa National Park rode the current to test a long-held theory that the vulnerability of wildlife species to flooding is linked to their body size, dispersal ability and habitat preference.
Idai made landfall on March 15, bringing strong winds and rapidly rising floodwaters that killed more than 1,600 people and caused more than $3.2 billion worth of infrastructure damage across Mozambique, Zimbabwe and Malawi. Staff and vehicles from Gorongosa National Park were deployed to help with rescuing and supporting affected communities in the surrounding area.
Parts of the park itself, which lies in the Pungwe River Basin in central Mozambique, flood annually, and the animals there are adapted to these seasonal events. But with the cyclone, the extent of flooding in the park expanded from 24 to 117 square kilometers (9 to 45 square miles) in the space of a week. As wildlife populations scrambled to avoid the swiftly rising floodwaters and then survive in the storm’s aftermath, scientists working in the park found themselves with an opportunity to observe the vulnerability of different species.
“In Gorongosa, we were in a unique position to do the study, because we had a group of researchers running simultaneous projects on a variety of different species for different reasons — including animals equipped with GPS collars to track their locations, detailed information on the animals’ prior movements, diets, and body condition, and data on their patterns of abundance before the cyclone,” Robert Pringle, a professor of ecology and evolutionary biology at Princeton University in the U.S. and part of the 18-member research team, told Mongabay in an email. Pringle and his colleagues published their findings in the journal Nature in November 2023.
The perennial floodplain around Lake Urema in the center of the national park, features both trees and grassland, and supports a large portion of the park’s wildlife. Surrounding this is a drier plain and savanna landscape dotted with palms, fever trees (Vachellia xanthophloea) and white acacia (Faidherbia albida), and areas of savanna woodland that seldom flood and have a good tree canopy cover.
The group had fitted collars to 13 different mammal species and set up camera traps. Along with sensors that tracked flood depth, the researchers were well-placed to evaluate the effects of the cyclone on animal distribution. They compared the collared animals’ behavior in the hours, days and months after the cyclone with data from both immediately before the storm and during the corresponding season in years when the park was hit by average flooding.
Unsurprisingly, they found that species that are naturally associated with wooded, higher ground were more resilient to flooding than those that preferred low-elevation areas. A November 2020 survey of the vastly expanded floodplain following Idai recorded declines in populations of several small-bodied species — the first declines recorded since wildlife began to rebound from widespread killing during Mozambique’s 1977-1992 civil war. For example, numbers of oribis (Ourebia ourebi) and reedbucks (Redunca arundinum), small, floodplain-bound antelopes, declined by 47% and 53% respectively.
On the other hand, populations of three larger species that favor the same low-lying habitat — wildebeest (Connochaete, s taurinus), buffalo (Syncerus caffer) and elephant (Loxodonta africana) — each increased by around 27%, supporting the long-held theory that large-bodied species are able to avoid floods by moving upslope.
Populations of large-bodied species like elephants increased by around 27% following floods caused by Cyclone Idai. Image courtesy Gorongosa National Park.
Fitting a lion with a radio collar. Researchers are tracking 13 different mammal species in Gorongosa. Image courtesy Gorongosa National Park.
Marc Stalmans, the science director at Gorongosa National Park, said alongside drowning and temporary displacement, the cyclone affected the animals’ food availability.
“Indirectly, some areas that remained submerged for several months lost their grass cover and thus the grazing was not available when the waters finally subsided,” Stalmans told Mongabay.
In the aftermath of the flooding, large animals coped better with limited vegetation to graze or browse. The researchers used satellite imagery to assess changes in food availability; analyzing dung samples collected over the course of 2020, they found the floods had significantly altered animals’ diets.
Almost all species the researchers monitored ate different plants throughout 2019 from what they ate in 2016 and 2018. After the cyclone, smaller animals found little to eat in flooded areas. Species such as bushbuck (Tragelaphus scriptus) and nyala (Tragelaphus angasii), which weigh less than 100 kilograms (220 pounds), were found to be in worse nutritional condition in 2019 than they were in the years before the storm, while kudu (Tragelaphus strepsiceros) and other large and wide-ranging species with similar dietary habits as the smaller ones were unaffected.
The researchers conclude that the larger herbivores were more resistant to nutritional limitations because of their ability to rely on natural, in-built reserves and subsist on low-quality diets.
According to the researchers, their study helps to shed light on how escalating severe natural turbulence affects wildlife populations and ecosystems.
“Our study contributes to a knowledge base that people can use to make both risk assessment and decisions,” Pringle said. “Because in principle, there are things that can be done. But one needs to be able to make an informed decision. What is the nature of the risk? Which species are most vulnerable? Will the benefit of an action, however extreme, be worth the cost?”
The researchers say further research will be needed to confirm their conclusions, expanding the sample size and continuing observations to see which changes persist. For instance, small-bodied species’ faster rates of reproduction might enable rapid recovery of populations, reducing the costs of lower resistance over time and matching these smaller species’ overall robustness to that of larger animals.
For Gorongosa National Park’s science director, the research can help guide planning and management.
“That knowledge can be used to guide the formulation of rewilding strategies in terms of the numerical balance between species,” Stalmans said. “It can also assist with the design of protected areas and of reintroduction bomas to allow for sufficiently high ground to surround any flood-prone, low-lying areas.”
Map of 2019 flooding courtesy of Gorongosa National Park.
Nikhil Advani, director for climate, communities and wildlife programs at WWF, described the study as “practical.”
He said many approaches to analyzing vulnerability of wildlife to catastrophic events rely on modeling how projected changes in climate may impact species.
“The trait-based approach employed in this study takes into account biological features of a species which makes them resilient or vulnerable to a changing climate,” he said.
Advani, who was not involved in the study, said that as Southern Africa experiences more extreme weather events, understanding how this affects species and ecosystems is increasingly important.
“We know that these extreme events are becoming more frequent and/or severe, driven by a changing climate,” he told Mongabay. “Policymakers and conservationists need to develop and implement strategies to adapt to these extreme events, employing tactics such as scenario planning, and translating research into on-the-ground solutions.”
Banner image: The number of small, floodplain-bound antelopes like this oribi (Ourebia ourebi) declined by 47% following flooding of Gorongosa National Park. Image by Manuel Schwarz via Wikimedia Commons (CC BY 4.0).
Citation:
Walker, R. H., Hutchinson, M. C., Becker, J. A., Daskin, J. H., Gaynor, K. M., Palmer, M. S., … Long, R. A. (2023). Trait-based sensitivity of large mammals to a catastrophic tropical cyclone. Nature, 623(7988), 757-764. doi:10.1038/s41586-023-06722-0
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This article was originally published on Mongabay
