For our next foray into the Pining for the Field series, I’ll take a look back to 2006 when I travelled to Cabo Rojo National Wildlife Refuge to study Smooth-billed Anis.



I remember flying into the airport and the air was heavy, further weighing down my backpack which was filled to bursting with everything I’d need for the next several months working in the field.


Dr. Jim Quinn of McMaster University, renowned for his long-term work studying smooth-billed anis in Puerto Rico, picked up my new acquaintance and fieldmate Eric and I from the airport. Jim drove us across the island, over the lush mountains, dripping vibrant green to puertofreako-043-2the southwest corner of the island. In stark contrast, this section of the island lies within the subtropical dry forest belt and looks like the African savannah dotted with acacia and mesquite trees. More than 200 years of overgrazing has led to much of the land becoming overrun with invasive species including the dreaded, leg-ensnaring buffel grass and the monstrous guinea grasses that grow taller than I could ever hope to be. But through habitat management, this refuge is providing a protected ecosystem for local wildlife, wintering migrants and endemic species including the yellow-shouldered blackbird, which is found nowhere else on earth. The refuge is even specially designated as Critical Habitat for this particular endangered bird.


puertofreako-033But the bird we were concerned with was one that wasn’t in any kind of critical condition as far as population goes, as Smooth-billed Anis do quite well in and around areas of cultivation and are common in the tropics of Central and South America. But these feisty characters are worthwhile for study thanks to a barrage of fascinating character attributes.


Anis are a communal species that lives in groups of as many as seventeen birds or so. On the refuge, we had more than ten different territories marked out that we determined by tracking birds we’d captured previously and fitted with radio-transmitters, one per territorial group. This way we could easily locate and observe the individual groups and it helped us find their nests which were monitored throughout the season.


puertofreako-006What’s particularly unique about these birds is that each territory will communally build a nest of sticks high in the trees and subsequently, every egg-laying female in that group will add her own ovo-contributions to that sole nest. With their joined forces, a smooth-billed ani nest has been known to boast up to 36 eggs. I recall climbing up the rickety 20ft ladder that, despite my comrades holding it from the bottom, swayed along with the branches against the breeze. Upon reaching the top, I’d peer into a nest to discover a multitude of white eggs, each about the size of a half dollar coin. I’d collect them into a soft bag and lower them to be measured, labeled and swabbed for DNA sampling as a means of figuring out which birds were laying the most, which was surmised to be based on a sort of female hierarchy.



Over monitoring the course of laying, we saw some eggs develop robin-egg blue scratches indicating at attempts to exude the egg from the nest. While the benefits of social living remain preferable – working together, looking out for each other – there still remains an instinctive desire within the females to pass on their own genes. Competition has developed in which the ladies will kick out the egg (the more unsuccessful attempted expulsions of an egg become evident as more and more of its milky coating is scratched away, revealing the blue beneath) before settling down to lay her own!

What’s more, these rascally females are even known for covering up a previously laid clutch by placing a layer of leaves over them and then adding her own to the new “empty” nest. There have been nests found to be as many as eight layers deep, but only the top uncovered layer can be properly incubated by parents to hatching.


Exerpt from Birds are Far From Boring:

These strategies of competition allows for a better guarantee that the female and her mate will pass on their genes in the formation of the next generation. This may seem in contradiction to the sociality of these birds, that living in a social group provides better protection than if the birds lived solitarily. Nevertheless, the benefit of single birds within the social group would be that they are less likely to be preyed upon and therefore live to reproduce and, once in the act of egg laying, will further the chances of passing on genes.


Despite the competition, the babes that make it through the egg stage of life start to hatch in profusion, as we delightedly climbed the ladder day after day only to discover another handful of squirmy, wrinkled, naked chicks that have newly emerged from their egg. We visited each nest regularly puertofreako-195to note hatch date and started to measure chick growth.  Part of the study that we were participating in included taking blood samples of the chicks which could be matched to DNA samples gathered from swabbing the eggs, thus giving information on individual female productivity success using genetic markers in an examination of the complex mating system and reproductive tactics of these birds. While there is definitely a system of hierarchy going on, there’s still more to be learned.


While watching these birds over the course of the breeding season, between September and the end of November, we became familiar with the different groups, where they liked puertofreako-055to hang out, what were the best feeding patches where the lizards and insects skittered around in the grass, what trees they liked to roost in for the night. We spent a good deal of effort determining this because, by finding their roost tree, we could attempt to trap these wily birds so that we could place colored leg bands on for easy identification in the field. It was not a simple task. It meant that you had to follow the group for the entire evening, without disrupting them, as they decide upon a roost and then you must wait until they are seemingly settled in for the night before creeping silently away with the tree firm in your brain. Long before dawn, we’d slink back out as a group, netting and puertofreako-007banding equipment in hand to the roost tree. To capture these birds by this method, a lot of guesswork is involved as to where to set up the extend-a-pole nets that we situated in front of the tree in hopes that was the direction they’d exit at sunrise. Using headlamps, we worked as quietly and quickly as possible to set up the twenty-something foot high nets and then retreated into the undergrowth to wait for the first glow of the rising orb.



Yes, we got skunked several times. But when they do come flying out in the direction you’d so fervently hoped and flop into the giant, baglike mist net, the action starts. We all have a job, one person at each pole as quick as possible (we come blasting out of the grass, let me tell you) so as to rapidly de-extend it and the net flops over itself before the wriggling birds can escape. Then there’s the one or two people designated to extract the bird from the pile of soft net it’s now under while the other begins the banding process. While our success rate made it hardly worth the hours we put in, it was fun! That is, until the great pigeon massacre where we watched the anis fly out the tree in the totally opposite direction from what we’d determined while handfuls of pigeons pouring out of the tree pelted our nets, leaving us a mess of confused non-target birds to detangle and set free.


Bycatch is inevitable and sometimes frustrating, but it give a chance to have some neat views of birds in the hand.


Clockwise from top left: Bananaquit, Northern Mockingbird, Blackpoll Warbler


As the nesting season wore on, we noticed some intense interactions among these highly defensive territorial groups, particularly at the boundary edges where two groups meet. Sometimes it’d be violent individual scuffles or the whole colony would aggressively torment an intruding spy until it retreated. The birds were often protecting, or attempting to expand, their territory. We had one group that persistently snuck into another group’s nest to crack eggs and actually maul the chicks, perhaps trying to drive out the colony from some prime habitat. One day we witnessed an invasion of one entire colony into a next door territory and a great battle ensued. This is what I love about fieldwork: you become part of nature, watching it so closely day after day that you become a part of it and it feels natural and you find yourself at home. You see things that few people have ever witnessed and you’re learning constantly through observation.


There is such great drama in the lives of the Smooth-billed Ani and I quickly grew very attached to them and that beautiful little corner of Puerto Rico. If you ever get out to the island, please check out the refuge and be sure to say hi to my birds!


More bird job stories to come, stay tuned and thanks for reading!


All photos by @stacebird

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