Meet the scientist
Research associate, University of Illinois at Urbana-Champaign When a beloved tree toppled spectacularly at his field site in Panama, Henry Pollock’s disappointment quickly turned into excitement about a new and unique opportunity to study a variety of sp
Ornithologist Henry Pollock tells us about his fieldwork in Panama
The toppling of a giant – whether it’s King Kong, an elder statesman or a decommissioned cooling tower – is likely to bring a lump to the throat.
So it was when a huge tree fell in a patch of Panamanian rainforest used by generations of University of Illinois biologists to assemble one of the longest-running bird-netting surveys in tropical America.
As it happens, no one was around to hear the emergent tree fall, but on the evidence of the hole it rent in the fabric of the forest, the noise would have been considerable.
“It took a bunch of other trees with it, wiping out a huge swathe of about 2ha,” says ornithologist Henry Pollock. He describes the reaction of his senior colleague, Jeff Brawn, when they inspected the damage: “He was crestfallen – really upset about it. He said ‘Oh, man, I’ve been walking past this tree for 30 years, and now
it’s gone.’”
But ends are also beginnings:
“It turned out to be a unique opportunity,” says Pollock. “We carried on with the netting routine, and started catching all these hummingbirds. One species, the snowy-bellied hummingbird, had never been caught before during the entire 44 years of the project, and yet we netted 16 of them within days.”
Over all, the total diversity of hummingbirds caught at the site more than doubled. Frugivorous birds, such as red-capped manakins, also increased.
The sudden loss of the canopy flooded the understory with light, creating conditions for species to flourish, flower and fruit.
“It all happens pretty quickly,” says Pollock. “It seems that the birds are prospecting around the forest and when they stumble upon a gap with their preferred food sources – nectar and fruit – they stay put.”
But not for long. “Within a year for the hummingbirds, and within three years for the frugivores, they’d gone again,” Pollock says. “These gaps are really useful for the forest, but they are ephemeral, so regular ecosystem disturbance is essential if these birds are to persist in the landscape.”
The biologists’ foray into the ecology of treefalls was also shortlived – a case of right time, right place. The routine netting, ringing and monitoring of long-term population trends continues, though COVID-19 is now making even that far from straightforward.
While travel restrictions are in place, Pollock is working on a paper about the longevity of rainforest birds, something that is only possible because of the long-term nature of their unique dataset. “We catch the same birds over and over again,” says Pollock.
Meanwhile, there’s not much left of the fallen giant. “That had mostly gone after two years,” says Pollock. “Stuff gets recycled really fast in the tropics.” Stuart Blackman
S One species hadn’t been caught before during the project and yet we netted 16 of them within days. T