For eight years, northern Blue-throated Macaws never showed interest in nest boxes put up for them at Barba Azul Nature Reserve, a protected area managed by ABC's Bolivian partner Asociación Armonía. What makes this more perplexing is that to the south, Blue-throated Macaws love nest boxes. At the Laney Rickman Blue-throated Macaw Reserve, the macaws have used 26 nest boxes, fledging 81 chicks in the last 13 years.
Armonía began, with assistance from ABC and other organizations, placing nest boxes at Barba Azul in 2009. Until now, not a single macaw came close or showed any kind of interest in these new homes. We copied the same characteristics of successful nest boxes at the Laney Rickman Reserve, especially of a preferred height of around 13 feet above the ground, but without success. In 2012, hypothesizing that the problem was that the birds did not like nest boxes near large, closed forest, we put 50 nest boxes within small, isolated palm forest islands along Rio Tiniji. But, again, we never once saw a Blue-throat approach, chew, or show any kind of interest in the nest boxes.
This is frustrating because Armonía worked with ABC and other partners to establish the 27,100-acre Barba Azul reserve, which conserves food resources and roosting sites for the Blue-throated Macaws. So it's vexing to have none of the them stay to breed on the reserve. All the Blue-throats have been flying off in November to nest in what we assumed were palm tree stands on cattle ranches north of Barba Azul.
In 2017, Tjalle Boorsma, Armonía's Conservation Program Director, led a research party about 50 miles north of Barba Azul, searching for breeding birds. He discovered breeding Blue-throats but with a very different nesting behavior: The nesting cavities, more like open divots, were placed around 40 feet above ground on top of isolated dead royal palm trees. This was nothing like the preferred nesting holes of the southern Blue-throated Macaws at the Laney Rickman Reserve. In a nutshell, they were breeding in cavities about three times higher and in open situations much more isolated from other trees.
Knowing that macaws are very smart birds, that a lot of their behavior is learned and not innate, we thought we needed to rethink our whole nest box approach for these northern birds — and that the solution would be to imitate, if not improve upon, the newly found high cavities.
Thankfully, ARTIS Amsterdam Royal Zoo, IUCN-Netherlands, and Mohamed bin Zayed Species Conservation Fund trusted our “out of the nest box” thinking and supported our project to create high penthouse nest boxes. Implementing this plan included transporting from the Bolivian highlands ten 40-foot-long eucalyptus poles.
We were able to raise five penthouse nest boxes in 2018 and we have another five that will be raised this year, once the ground is dry enough. Tjalle, noticing Blue-throated Macaws have a predictable sunset flight path to their roosting site, decided to place the nest boxes directly in their path.
About a month ago , Barba Azul reserve guard Carlos Roca reported that he had seen a pair of Blue-throated Macaws perching and investigating a penthouse nest box. And three weeks ago, Tjalle observed three different Blue-throated Macaw pairs not just perching on our nest boxes but entering the hole and squabbling over the prime real estate.
Nest cavities are a much scarcer resource than most bird-nesting sites. Naturally large nest cavities are rare, but in our modern world, where most large trees are cut for timber, they are truly a limiting factor in macaw reproduction. Many macaws will identify a breeding cavity many months before they are ready to breed. They will continually observe it and visit it every day to make sure it is safe. This has been documented in many macaw species.
Often, these favored cavities are reused over and over again. So, the fact that these birds are really noticing these nest boxes, observing them, perching on them, going in and even sort of gently fighting over them, really gives us hope that they may use them to nest. We will keep a watchful eye on these penthouse nest boxes and hope that the birds decide to stay in November to start breeding, achieving for us full-life-cycle conservation of the species at the Barba Azul Nature Reserve.
Bennett Hennessey is ABC's Brazil Conservation Program Coordinator. He has worked extensively in Bolivia, including at Asociación Armonía's Blue-throated Macaw Reserve.