By David Millican
It’s late January in central Namibia, the time of year when heavy rain showers become a regular source of relief for many animals. If the rains arrive, a green carpet spreads across the landscape and food becomes plentiful for all, providing the necessary resources for many species to reproduce. If the rains fail to show, dehydration and starvation sweep through the land like a plague. All individuals suffer, but the young and old, the weakest and most vulnerable, become the most common victims to drought. During these times, pining parents will often fail to rear offspring and may forego breeding altogether, forced instead to focus entirely on survival.
I’m outside Otjiwarongo, studying the local cavity-nesting guild, a specialized and highly diverse community of animals that use tree cavities for nest sites. Found in forests worldwide, cavity-nesting guilds are composed of mammals, reptiles, amphibians, invertebrates, and, my favorite, birds. I will call this area home from December through May over the next few years as I attempt to understand the structure of this particular cavity-nesting guild. Do certain species prefer certain types of cavities? How do species interact with each other while competing for cavities? How might human management impact these communities, and how can we ensure that our actions don’t jeopardize their persistence?
Hopefully I can strike it rich and obtain crucial insight into these questions. But before I can strike gold, I must first strike water. Dams have been empty for months, parched from a drought the previous year, and withered carcasses become more and more common sites in the field. Everything is looking to the sky for rain, myself included. If I’m to have any success in my research, I need the rains to come and help kick start the breeding season.
On this afternoon, it seems prayers have been answered. Two hours after gray clouds first crept into view, the sky is a dark, bulging waterbed waiting to burst. Before you can grab your raincoat, the monsoon begins. Downpouring, deluging, raining cats and dogs; throw out your best idioms, just run for cover as you do. The storm doesn’t last long, thirty minutes at most, but that’s plenty of time for two inches of rain to fall. Rivers form wherever they please, Oryx splash about like children at a water park, and hope is seemingly restored to the land.
In the days following the rain, the landscape is vastly transformed. The previously barren earth sprouts a green mane, while acacia trees finally look more leafy than thorny. Animals have also responded. Roadside puddles are filled with enormous African bullfrogs, Leopard tortoises race across roads with re-energized vigor, and the hordes of antelope, once concentrated in mass at man-made water holes, are nowhere to be found, having dispersed to newly formed pools throughout the landscape. The birds are lively as well. Prospective passerines gather grasses to build nests within barbed branches. A second visit to our nest boxes reveals that almost a dozen new female hornbills, the largest cavity-nesters here in Namibia, have begun to build. Things are looking up.
But it’s still too early to say if the weather will be fruitful. One heavy rain is far from adequate for the animals here, which are accustomed to and hoping for regular downpours from December through April. If only they knew the weather projections.
A strong ENSO (El Niño Southern Oscillation), as is predicted for 2016, usually correlates with even drier weather in southern Africa. So while California finally climbs out of a drought, Namibia may be set to plunge deeper into its own.
To make matters worse, climate change models predict increasing aridification of Namibia over the coming century. This means less annual rainfall, and more frequent and severe droughts. The current circumstance may severely hamper my own research, but these projections intensify the overall need for research on cavity-nesting guilds. How will species respond to more frequent droughts? How will less rainfall impact tree growth and cavity availability? How will these changes alter the interactions between species? If there is to be any hope of preserving these communities, it is vital that we understand their structure so that efforts can be made to maintain them.
Ph.D. Student, Department of Biological Sciences, Virginia Tech
Interfaces of Global Change Fellow
Photos of cavity dwellers in Namibia (in chronological order): (1) Yellow-billed hornbill, (2) grey-billed hornbill nestings in box