Tagging Amazonian birds led to harness improvements
The calendar read 1979 when the Biological Dynamics of Forest Fragments was founded to study the effects of forest fragmentation on Amazonian biota. Back then, to arrive at the BDFFP, you had to trek for hours up BR-174—a muddy dirt road snaking north of the Brazilian city of Manaus. For the ornithologists charged with establishing the experimental plots, traveling through the rainforest without getting lost meant relying on a compass and machete chip marks on trees. Under the tall canopy of Amazonian lowlands, a map is of little use. GPS units capable of operating under these conditions were still two decades away.
Nearly 40 years later, I was about to venture to the BDFFP myself to do my dissertation research. BR-174 was paved, and other technology advances have since transformed the world—ornithology included. I had miniature dataloggers and the objective to tag 10 species of terrestrial insectivores inhabiting the still-vast primary forest surrounding the BDFFP. Another shift in the last four decades, as we have found, was that these species have inexplicably declined. My goal now was to understand why, using measurements from three tag types. I and my team had to locate these rare species, deploy tags, and then recapture them in the following years to ‘harvest’ the data. This plan raised several concerns, the first of which was my location—I was sitting in Louisiana. For non-Brazilians, starting research at the BDFFP meant arduous permitting process that already cost me two field seasons. With constricted timeline and no opportunity for field trials, how do we attach tags to birds of various sizes? Harnesses for these tags needed to withstand the harsh environment for at least a year while not harming the birds—for their sake and for the sake of our data.
The JFO paper titled “Adjustable leg harness for attaching tags to small and medium-sized birds” is the outcome of this predicament. In this publication, we adapt the widely used Rappole & Tipton leg harness to make it easily field adjustable. After finally arriving at the BDFFP, this let us hit the ground running—once we found the right bird, fitting the harness to an appropriate size was a matter of a few minutes.
But finding and catching the right bird was the slow part. For this we used playback and trawled the forest—speaker at hand—for days on end. My advisor Phil Stouffer, who inducted me into Amazonian ornithology after his three-decade tenure at the BDFFP, was nearly driven mad by the continuous blaring of Black-faced Antthrush vocalizations. Other species, like the Black-tailed Leaftosser, are even less melodious. If and when the right species responded, we set several mist nets in a ‘V’ formation, and then tried to lure the bird into the middle. True to their name, terrestrial insectivores—antpittas, antthrushes, antbirds—tend to fly little. This makes them hard to catch in mist nets, a reality which called for additional arrangements. A typical scenario would have us set nets, place the speaker in the middle, and then hide. After what could be hours while the bird nonchalantly ambled through the forest unseen, it might suddenly pop up next to the speaker. This was the moment for what I describe in academic publications as ‘eliciting flight response’—a euphemism for exploding from hideout and crashing through the understory like a lunatic towards the bird. If it flushed and got caught, the day was good, but frequently the bird got away and the process had to be repeated—often unsuccessfully. Either way, the thorns we implanted through eliciting flight response were to be extracted during the months following field work.
Things got even harder when we tried to recapture tagged birds in the following years. These species are made to survive the perils of Amazonia and learning from mistakes is one consequence—catching them the second time was even harder. Additionally, we found them to normally have massive home ranges. For example, we recaptured one Black-tailed Leaftosser—the rarest of our target species—2.5 km from its original tagging location. Draw a circle with this radius around each capture and that is a lot of rainforest to comb, especially with few trails. Particularly during tag recovery, maximizing trapping success was thus very important. To this end, co-author Bruna Amaral made a major improvement—concealing under camouflage, which let us stay very close to nets and pounce at the best possible moment. The disguise worked well, as demonstrated by an ocelot walking within a few meters of Bruna, so military-style camo netting was on the gear list from then on.
My respect goes to the ornithologists and other researchers who did great work in Amazonia without the now-available tools. The modern GPS units we carried had digital elevation models depicting local topography and were accurate to within 10 m—we could venture off trails without worry. These also enabled us to quantify the effort for our one to two field teams: 257 field days of capturing and then recapturing birds, during which we walked 3830 km—roughly the distance from Los Angeles to New York City. This endeavour let us deploy 90 tags and recover 43 (48%) of them. Importantly, the mass of birds at tag recovery was not lower than at tag deployment, and we did not find any other undesirable effects of tagging. This suggests that birds did well with the harness we described in the paper—we think because the approach enables proper fitting. As further technological advances expand the array of devices available for birds, deploying these properly should remain a priority, and our paper brings offers some guidance on that front. Perhaps the leaftosser racket was worth it.
This research was recently published in the Journal of Field Ornithology:
Jirinec, V., P.F. Rodrigue,s and B. Amaral. 2021. Adjustable leg harness for attaching tags to small and medium-sized birds. Journal of Field Ornithology. https://doi.org/10.1111/jofo.12353
Guest post by:
School of Renewable Natural Resources
Louisiana State University and LSU AgCenter
Biological Dynamics of Forest Fragments Project
Instituto Nacional de Pesquisas da Amazônia (INPA)