The Sapayoa, a rainforest bird from Central and South America, has long been an evolutionary enigma. Genetic analyses indicate that this species is alone in the Americas: its closest relatives live on the other side of the ocean in Southeast Asia. More recently, field research finds that despite its temporal and geographic isolation, this bird shares many of its peculiar natural history traits with its closest genetic relatives half a world away.

The Sapayoa is the only bird in its taxonomic family living in the New World

The Sapayoa (pronounced: sah PAY oh ah), Sapayoa aenigma, is a small, sedentary yellow-green songbird that resides in the dark understory of lowland evergreen rainforests extending from the Caribbean Sea in Panama and along the Pacific coast of Colombia, and just barely reaching the northernmost corner of Ecuador. This species is slightly larger and more slender than a sparrow, and it has an unusually wide beak. The Sapayoa is slightly sexually dichromatic: the males have a bright yellow cap on top of their heads that the females and juveniles lack.

As its scientific name implies, this bird has long puzzled ornithologists and taxonomists because they have been unable to identify its precise evolutionary relationships. Originally, this bird was placed in the manakin family (Pipridae) of New World suboscine songbirds on the basis of similarities in plumage and toe morphology (ref). But later, molecular data indicated that, despite certain physical similarities, the manakins and Sapayoa were not related.

Many decades later, several research teams removed the Sapayoa to a very different group of songbirds based on genetic data.

“[P]reliminary DNA-DNA hybridization comparisons … indicate that this species is either a relative of the Old World Eurylaimidae or a sister group of all other Tyrannida, as suggested by earlier biochemical studies … In any event, it is not a close relative of manakins or any other recent tyrannoid” (ref).

Additionally, it was found that the structure of muscles in the bird’s “voice box”, the syrinx, also resembled the Old World Eurylaimidae, particularly the broadbills in the genus Eurylaimus. The syrinx comprises a specialised group of muscles located at the base of a bird’s trachea that it uses to produce songs. The structure of the syrinx is so distinct that it sets songbirds apart from all other avian groups.

Other researchers noted that the Sapayoa’s skull structure most closely resembles the skulls of broadbills in the genus Eurylaimus that live in Southeast Asia.

At this point, there was much head-scratching: how could a South American bird look so much like a group of birds found on the opposite side of the Pacific Ocean many thousands of miles away? Just who are the Sapayoa’s closest relatives?

Currently, the New World Sapayoa is the only representative in the taxonomic family Sapayoidae (ref), which is placed in the Old World suboscine lineage. Despite this advance in our understanding, we still aren’t sure who its closest relatives are: is the Sapayoa related to the broadbills of Southeast Asia (genus: Eurylaimus; ref)? Or perhaps it is closer to another Old World genus, Pitta (ref)? Or maybe another Old World group, the green broadbills (genus: Calyptomena), are its closest living relatives (ref)? Or the enigmatic Sapayoa could be an early evolutionary offshoot from — and thus, a distant relative to — all other Old World suboscines (ref).

We just don’t know. At this point, the one thing that we do know about the Sapayoa is that it is an Old World bird species living, in apparent isolation from all of its relatives, in a New World rainforest.

Sapayoa behaviours provide additional clues to its identity

Because Sapayoa live in rugged and remote areas, and are fairly scarce, it’s not surprising that we don’t know much about their life history and reproductive biology. But last year, Sarah Dzielski and Benjamin Van Doren, both undergraduates at Cornell University at the time, conducted a field study with the goal of learning about this mysterious species’ breeding biology, under the supervision of Cornell alumni, Jack Hruska, now a graduate student at University of Kansas, and Justin Hite.

“The Sapayoa is so different from other passerine birds that it is currently placed in its own family, Sapayoidae, but relatively little is known about its natural history,” said the study co-author, Mr. Van Doren.

“This gap in scientific knowledge was the reason we traveled to eastern Panama to learn about this enigmatic species. We hoped that more information about the Sapayoa’s natural history would cast its surprising evolutionary relationships in a new and clearer light.”

To conduct this study, the team of researchers established a field camp during the summer of 2014 in the remote Darién National Park of eastern Panama near the Colombian border. During their field surveys, the team spent a month in the field searching for nests, discovering two active Sapayoa nests and 13 old nests.

“Nest searching was always an adventure,” said the lead author of the study, Ms. Dzielski.

“While checking inside for eggs or evidence that the nest was active, we found all sorts of surprises. In a few instances, a large grasshopper the size of a mouse hopped out from under the flap and scared the daylights out of us!”

Sapayoa nests are pear-shaped hanging structures with long strands of fibrous material dangling from the bottom, and hang from a branch with live leaves from the branch falling over the nest entrance, which is a hole in the side. All nests were similar in structure to the only previously known nest. All the nests that the team found were all suspended over steep, rocky ravines with water running through them.

The team also observed one active nest for more than 70 hours over 10 days. and recorded the birds’ behaviours. The team noted that only the female brooded the chicks. But much to their surprise, they quickly learned that Sapayoas are cooperative breeders: at their nest, they observed two immature male birds assisting an adult pair feeding their young.

Well, usually.

“Oddly, the younger males in the group occasionally arrived at the nest with food but left without feeding the young — sometimes even eating the food themselves,” said Ms. Dzielski.

“This could represent ‘fake-feeding,’ when birds bring food to the nest to appear like team players, but sneakily eat it themselves,” explained Ms. Dzielski. “It’s also possible that the young males were simply balancing the needs of the chicks with their own hunger.”

The team noted other unusual behaviours, particularly mounting, which was preceded by a conspicuous solicitation display.

“The male birds mounted the female (as if trying to copulate) multiple times a day, even though their nest already held two fast-growing chicks,” said Ms. Dzielski.

They also observed that individuals of the same sex would mount each other, a social behaviour familiar to dog owners, that apparently is designed to establish dominance and to maintain social cohesion in these birds.

“The males also mounted one another on different occasions, involving both the adult male mounting a younger male and one younger male mounting the other. This type of same-sex mounting is unusual in birds, but when it occurs it is often associated with social dominance,” Ms. Dzielski explained.

When feeding their growing chicks, the adults and their helpers often appeared at the nest in rapid succession, before disappearing for as long as 45 minutes at a time. Whilst collecting food for the chicks, the birds were either silent or out of earshot — probably foraging in mixed-species flocks.

Despite living in the Neotropics for millions of years, the Sapayoa still recalls its Old World roots with its behaviours. This field study highlights that many of the Sapayoa’s natural history traits — diet, nest structure, breeding system, and parental care — are basically unchanged from its temporally and geographically distant Old World relatives, the eurylaimid broadbills — and these behaviours contrast sharply with those of its neotropical neighbours.

The Sapayoa: STILL a riddle wrapped in a mystery inside an enigma

“The sapayoa has long been a mystery bird,” said Jon Fjeldså, a professor in biodiversity at the University of Copenhagen and curator of the bird collections at the Natural History Museum of Denmark, who first identified the bird’s unusual origins in 2003 (ref).

“When we identified it as the only Old World suboscine in the New World, it only became more mysterious,” Professor Fjeldså added.

Many of the Sapayoa’s closest relatives, the broadbills in the genus Eurylaimus, are cooperative breeders, and many are known to build pear-shaped hanging nests — just like the Sapayoa. But the Eurylaimus species are confined to tropical regions around the Indian Ocean, and no other member of the group has been found elsewhere.

“How did it arrive in South America?” asked Professor Fjeldså.

Although we still don’t know the answer to this question, it has been proposed that the Sapayoa is the last surviving member of an ancient New World lineage that originally evolved in Australia-New Guinea when Gondwana was in the process of splitting apart (55 million years ago) and sea levels were rising (between 8,000 and 6,500 BC), thereby separating Australia from New Guinea. The current hypothesis is that the Sapayoa’s ancestors may have reached South America by traveling along the Western Antarctic Peninsula.

“Why does it resemble a manakin?” Professor Fjeldså wondered aloud. “And does it still behave like an Old World suboscine? I am excited to learn that it indeed does!”

Source:

Sarah A Dzielski, Benjamin M Van Doren, Jack P Hruska and Justin M Hite (2016). “Reproductive Biology of the Sapayoa (Sapayoa aenigma), the ‘Old World Suboscine’ of the New World,” The Auk: Ornithological Advances 133:347–363 doi:10.1642/AUK-16-5.1

Also mentioned:

Jon Fjeldså, Dario Zuccon, Martin Irestedt, Ulf S Johansson, and Per GP Ericson (2003).

“Sapayoa aenigma: A New World representative of ‘Old World Suboscines'”, Proceedings of the Royal Society of London, Series B, Biological Sciences 270(2):S238–S241 | doi:10.1098/rsbl.2003.0075

Moyle, RG, RT Chesser, RO Prum, P Schikler, and J Cracraft (2006). “Phylogeny and Evolutionary History of Old World Suboscine Birds (Aves: Eurylaimides),” American Museum Novitates 3544:1–22 | doi:10.1206/0003-0082(2006)3544[1:PAEHOO]2.0.CO;2

Santiago Claramunt and Joel Cracraft (2015). “A New Time Tree Reveals Earth History’s Imprint on the Evolution of Modern Birds,” Science Advances 1(11):e1501005 | doi:10.1126/sciadv.1501005

Martin Irestedt, Jan I Ohlson, Dario Zuccon, Mari Källersjö, and Per GP Ericson (2006). “Nuclear DNA From Old Collections of Avian Study Skins Reveals the Evolutionary History of the Old World Suboscines (Aves, Passeriformes),” Zoologica Scripta, 35(6):567–580 | doi:10.1111/j.1463-6409.2006.00249.x

Per GP Ericson, Seraina Klopfstein, Martin Irestedt, Jacqueline MT Nguyen and Johan AA Nylander (2014). “Dating the Diversification of the Major Lineages of Passeriformes (Aves),” BMC Evolutionary Biology 14:8 | doi:10.1186/1471-2148-14-8