Rainforest transformation impacts reproduction among cavity-nesting birds

Deep in Ecuador’s Mache-Chindul Ecological Reserve, researchers used an extendable pole equipped with a tiny camera to explore the world of cavity-nesting birds. This is a world threatened by rapid deforestation and agricultural expansion.

Dr. Alison Ke, a UC Davis graduate, led an investigation into the impacts of rainforest-to-farmland conversion on birds that depend on tree holes for nesting. 

How the research was conducted 

Working with local scientists, community members, and the Ecuadorian NGO, Fundación para la Conservación de los Andes Tropicales, Dr. Ke’s team conducted bird surveys, studying natural tree cavities present in both forest and agricultural landscapes.

Over nearly three years, from September 2019 to June 2022, the team erected 100 nest boxes, splitting them evenly between forested and pasture areas. These boxes received nearly 11,000 visits. 

“We’d stick the camera in, and we’d never know what to expect,” said Dr. Ke. “Every time it was something new; it was very exciting. And when eggs appeared but we didn’t know what species it was, it was like a mystery we got to solve.”

What the researchers discovered 

Published in the journal Biotropica, their findings were both enlightening and alarming. Deforestation wasn’t just depriving birds of their homes – it was impacting their reproductive capacity. 

“When humans cut down forests for farming, it destroys their nesting habitat,” explained Dr. Ke. “There are some species that might just disappear if we cut down the forest. It’s extremely important to study the effects of agriculture on wildlife.”

While these birds frequented tropical pastures, they often struggled to find adequate nesting resources, which ultimately hindered their reproduction. 

Study implications 

The study revealed that eight species of cavity-nesting birds, including the house wren, dusky-capped flycatcher, and the Pacific parrotlet, were more abundant in agricultural settings. By contrast, the collared aracari, a toucan variant, was predominantly found in forests, likely drawn by specific food sources.

Daniel Karp, associate professor at UC Davis and the senior author of the study, emphasized the potential of leaving sporadic trees and integrating nest boxes into tropical agricultural terrains. Such interventions could be dual-purposed, benefiting both avian life and the farming community. 

“Our work shows that pastures often eliminate critical nesting habitat for tropical birds. However, by retaining trees in pastures and installing nest boxes, ranchers can provide crucial nesting sites for cavity-nesting birds, many of which might even benefit the farmers themselves by eating pest insects,” said Professor Karp.

More about cavity-nesting birds

Cavity-nesting birds are a diverse group of avian species that have evolved to nest within natural or excavated hollows, primarily in trees but also in other structures such as cliffs, ground burrows, or man-made structures. These unique nesting preferences provide these birds with protection from predators and environmental factors.

Characteristics and types

Natural cavities

Many birds use natural cavities, like those created by decay or broken branches in trees.

Excavators

Some birds, like woodpeckers, have the ability to chisel out their own nesting chambers in the soft or rotting wood of trees. Once they’re done using them, other birds might occupy these abandoned holes.

Secondary nesters

These birds utilize cavities that are naturally present or those abandoned by excavators. Examples include bluebirds, some owls, and chickadees.

Notable cavity-nesters

Woodpeckers

Known for their strong bills and unique drumming, they excavate cavities in trees to lay their eggs.

Owls

Species like the Eastern Screech Owl or the Western Screech Owl often nest in tree cavities.

Parrots

Many parrot species, including the Pacific parrotlet mentioned earlier, use tree cavities for nesting.

Bluebirds

They’re secondary nesters and often occupy old woodpecker holes or natural cavities.

Swallows

Some species, such as the Bank Swallow, dig burrows in sandy banks or cliffs.

Benefits of cavity-nesting

Protection

Cavities provide protection from many predators, as the confined space makes it challenging for larger animals to access.

Weather shelter

Tree cavities can offer protection from adverse weather conditions, maintaining a relatively stable internal environment.

Camouflage

The recessed nature of cavities can make nests harder to spot, especially from aerial predators.

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