Tuesday, August 22, 2017

The Hoatzin; strange bird becomes even stranger.

Birdwatching abroad is more than just returning home with a large checklist, it is also about observing bird behavior and recalling special moments. One moment in particular, though not recognized at the time as being significant, was the inspiration of today’s post.      

After four hours of canoeing the backwaters of the Napo River in Ecuador, our group decided to break for lunch along the banks of a picturesque lagoon. The location was a small hideaway where native Kichwa people often catch and prepare fish. Before pushing off from shore, I noticed a pile of large black bird feathers on the ground, which I picked up and placed into my field guide. I was told by my Kichwa friend that local people sometimes kill birds such as guan and hoatzin and use them as fish bait. A brief examination of the feathers by our elder guide mentioned that they were most likely from a Hoatzin.

Hoatzin
Ecuador
Photo Credit: Paul Cianfaglione
The Hoatzin (Opisthocomus hoazin), also known as the stink-bird, is a species of tropical bird found in swamps, riparian forests, and mangroves of the Amazon and the Orinoco Delta in South America. It is notable for having chicks that possess claws on two of their wing digits. The Hoatzin is an herbivore, eating leaves and fruit, and has an unusual digestive system with an enlarged crop used for fermentation of vegetable matter, in a manner broadly analogous to the digestive system of mammalian ruminants. The alternative name of "stink-bird" is derived from the bird's foul odor, which is caused by the fermentation of food in its digestive system (Source: Wikipedia). 

I took the feathers back home to the states with plans of adding them into my ever-expanding feather collection. An in-hand inspection prior to storage revealed something I’ve never seen before. Located on a few of the feathers were these peculiar protrusions on the underside of their rachis. At first, I thought the growths were caused by an outside source, but as I turned the feather on its side (under a microscope), it became clear that the protrusion had grown from the rachis itself (the black coloration of the rachis appears to bleed onto the side of the protuberance). I also thought the swellings may have been some kind of unusual deformity, except that I collected three feathers like this, all with nearly identical growth patterns and starting location near the calamus.


Hoatzin Feather no.1
Photo Credit: Paul Cianfaglione
 
Hoatzin Feather no. 2
Photo Credit: Paul Cianfaglione
Hoatzin Feather Rachis
Photo Credit: Paul Cianfaglione
Dumbfounded, I turned to Professor Alan Brush, an authority on feathers, who in the past has thoughtfully answered many of my past questions. 

Knowing that this would be an out-of-the-ordinary request, I decided to simply ask Professor Brush if these protrusions on the feather rachis were familiar to him, and if so, could he speculate on whether these growths play any significant role by being there? His response;

“either this is a recently molted feather, and the structure has not dried completely or there is some mechanical damage to the base that has opened the calamus. The problem is that all the material should be the same color. Plus, the inside doesn't look right. Could some extraneous materials have deposited in there?”


Hoatzin Feather Rachis
Photo Credit: Paul Cianfaglione
Obviously, this type of unusual growth is not normally found during feather development. I agree, the material should still be the same color. But as I mentioned earlier, the black coloration of the rachis, bleeding onto the lower half of the protuberance still bothered me. Despite this lack of uniformity in color, I still believe the black coloration, from rachis to protuberance, is proof that it actually grew from the feather itself, not once, but on three separate occasions.


Degraded Hoatzin Feathers
Two with rachis protuberance, one without
Photo Credit: Paul Cianfaglione
Could I speculate on why something like this would have grown from a rachis? No, not me, there is nothing I know of that would logically explain why three feather rachises would identically grow this way. 

Let us remember that these feathers are most likely from a Hoatzin, a bird with already many quirks of its own. So, growing a few bizarre feather rachises is not beyond the realms of possibility for this species. 

Feathers featured in this posting could possibly be highly degraded secondary feathers. See video below; 

https://www.youtube.com/watch?v=qlV4ypyvkW8&list=PL3RvdwOqyVvgA2lO4pT5RX1d-Hnpvauk_

The only way to truly find out if these rachis growths are normal is by a direct comparison with other museum feathers. Since I don’t see this happening any time soon, the odd-looking feather rachises will remain a mystery for now. 

During my online search for feather information, I was sidetracked by an unusual article on Hoatzin conservation titled; Sound the stressor: how Hoatzins (Opisthocomus hoazin) react to ecotourist conversation (Daniel S. KarpEmail authorTerry L. Root, 2009).


Since I was just an involuntary participant in this type of study, an ecotourist in the company of Hoatzins, this was an article I couldn’t pass up. The abstract below; 

Exposure to ecotourists often disrupts animal behavior, which is known to contribute to heightened mortality rates. In the Amazon, the emblematic, communal nesting Hoatzin (Opisthocomus hoazin) is frequently pursued by tourists eager for close views. Such encounters may cause heightened stress levels, and egg or nestling predation due to decreased parental attendance to nests and nestlings. The effect of reducing conversational tourist noise near wildlife is poorly understood, but represents one potential mechanism of mitigating the impacts of ecotourists on wildlife. In this study, we approached Hoatzins by canoe, playing recorded tourist conversations at different volumes. Both the distances from which we observed Hoatzins becoming agitated (e.g., clucking, defecation, etc.) and flush (e.g., flight or climbing away) were positively correlated with volume. Within 10 weeks Hoatzins began to habituate to silent approaches. Tourist conversations, however, continued to elicit the same heightened disturbance responses throughout data collection. Therefore, to have the best chance of seeing Hoatzins at a short distance and minimizing potentially negative disturbances, ecotourists should cease all conversation. Although not tested, silence is probably the best strategy when looking for many wildlife species. (End of abstract.)

My first reaction to this article was; do we really need a scientific paper to prove that a canoe filled with loud-mouthed ecotourists are a detriment to Hoatzin reproductive success?? To the authors credit, there probably were a few instances where guides and ecotourists should have been quieter, especially around active Hoatzin nests. However, when you look at the bigger picture here, the continual presence of Hoatzins around ecolodges and protected areas is a clear sign of avian acclimatization. 


Hoatzin on a nest
Ecuador
Photo Credit: Paul Cianfaglione
Personally, I find it almost hard to believe this bird continues to exist. Hoatzin are large, slow and not very aggressive. They nest in the open along the edge of lagoons where monkeys, snakes and eagles opportunistically hunt, as well as where piranha swim patiently below. 


Silver Piranha caught near Hoatzin nest
Ecuador
Photo Credit: Paul Cianfaglione
But if I had to think of a larger problem facing the Hoatzins today (and other large birds) it would have to be from the local hunters. The discovery of a pile of feathers at a fishing station and the admittance by native elders that Hoatzins are used as fish-bait is a sure sign of negative disturbance and higher levels of stress. 

Are native hunters really a problem to Hoatzins and other wildlife?? I was told by our guides that ecolodges actually pay (or cut deals with) the local communities to not hunt or fish their protected areas. In one instance, the lagoon where I was staying was once severely depleted of fish due to a few years of unregulated use. Actually, I believe ecotourists could be a benefit to the Hoatzins future nesting success by keeping protected areas honest.  

Saturday, August 5, 2017

Avian Nectar Robbers


Last month, I had the pleasure of traveling to Ecuador for two weeks with my wife and three kids. We birded in delightful places such as the Cloud Forest near Mindo and the Amazon Rainforest along the Napo River. Sandwiched between our stays in Mindo and Napo, was a trek up into the Andes to a region known as the paramo. 

The paramo is an ecosystem described as being situated above the continuous forest line, yet below the permanent snowline. Even near the equator, morning temperatures can be very cold in the High-Andes, a sharp contrast from our other two Ecuadorian destinations.



The Paramo in Cotopaxi National Park, Ecuador
Photo Credit: Paul Cianfaglione

In addition to the sightings of Andean Condor (Vultur gryphus), the most remarkable birds present in the paramo were the hummingbirds. Situated at an elevation of over 11,000 feet, our hacienda featured a small selection of birds, mostly attracted to the grounds artificial plantings. Yet hummingbirds, which were one of only a few species to inhabit the property, were not encountered every day.



Hacienda Porvenir, Ecuador
Photo Credit: Paul Cianfaglione

A species of bird that we did encounter daily was the Black Flowerpiercer (Diglossa humeralis). Flowerpiercers have upturned bills with a hooked upper mandible and pointed lower mandible. As its name implies, the Black Flowerpiercer pierces the base of flowers with its unique bill and extracts the nectar through the hole with its brush-like tongue.

 
Black Flowerpiercer, Ecuador
Photo Credit: Paul Cianfaglione

A nectar robber, which the flowerpiercer clearly is, avoids contact with the floral reproductive structures, and therefore do not facilitate plant reproduction via pollination. Because many species that act as pollinators also act as nectar robbers, nectar robbing is considered to be a form of exploitation of plant-pollinator mutualism (Source: Wikipedia).

Pollination systems are mostly mutualistic, meaning that the plant benefits from the pollinator's transport of male gametes and the pollinator benefits from a reward, such as pollen or nectar. As nectar robbers receive the rewards without direct contact with the reproductive parts of the flower, their behavior is easily assumed to be cheating (Source: Wikipedia).

In the paramo, the sole focus of the Black Flowerpiercer was the shrub Datura, otherwise known as angel trumpet. Datura grows fast, upright, and often forms an umbrella-like canopy, under which huge 10-inch trumpet shaped flowers descend. The flower opening can easily be 5 inches wide.

 
Black Flowerpiercer and Datura Flower
Photo Credit: Paul Cianfaglione

Given the size of both the flowerpiercer and flower, it wasn’t unusual to observe the bird hard at work creating holes and feeding on nectar. What was unusual however was seeing those same flowers and holes being used for nectar extraction by one of the local hummingbirds.

 
Hummingbird Secondary Robbing a Datura Flower
Ecuador
Photo Credit: Paul Cianfaglione

Wow, this was very interesting! Did the hummingbird learn how to feed from the created holes (base of the flower) by watching the Black Flowerpiercers behavior? Had the hummingbird exploited the flower and flowerpiercer, and become a nectar robber itself?


Hummingbird Secondary Robbing a Datura Flower
Ecuador
Photo Credit: Paul Cianfaglione

In other Central and South American settings, flowerpiercers are known to be attacked by territorial hummingbirds defending their feeding areas. Did the paramos harsh environment and limited resources create a more mutualistic relationship between the two species?   

There are two main types of nectar robbing: primary robbing, which requires that the nectar forager perforates the floral tissues itself, and secondary robbing, which is foraging from a robbing hole created by a primary robber (Source: Wikipedia).


Hummingbird Secondary Robbing a Datura Flower
Ecuador
Photo Credit: Paul Cianfaglione
But there is a slight twist to this fascinating story. In an online paper published in 1994 titled Serrate Tomia: An Adaptation for Nectar Robbing in Hummingbirds? author Juan Francisco Ornelas suggests that some hummingbirds may in fact pierce the base of flowers themselves with their short, serrate, hooked bill.


Yes, some hummingbirds do have bill serrations, but those were thought to be more of a function to facilitate the holding of insect prey, rather than that of a cutting tool. As luck would have it, I also had the opportunity to observe a Black-throated Hermit (Phaethornis atrimentalis) hover and gorge on a hatching of flying insects during this very same trip.

Some hermits show bill serrations like Androdon, although less pronounced. These corresponding anatomical features between hermits and Androdon probably reflect convergent adaptations to spider-catching and not a common ancestry. https://www.researchgate.net/profile/Karl_L_Schuchmann/publication/275089338_Taxonomy_and_Biology_of_the_Tooth-billed_Hummingbird_Androdon_aequatorialis/links/5580128e08aec87640df2303/Taxonomy-and-Biology-of-the-Tooth-billed-Hummingbird-Androdon-aequatorialis.pdf

Even though the author points out some interesting morphological similarities between the bills of flowerpiercers and hummingbirds (serrated tomia), there seems to be little evidence, other than eyewitness accounts, that prove that hummingbirds make perforations at the base of flowers to extract nectar. Past observations may have been misinterpreted as primary robbing, instead of secondary robbing.

The paper also presents an alternative behavior (which I believe is more likely) of the mutualistic relationship of flowerpiercers and some hummingbirds. Here is what is generally known about this type of behavior;  

Since nectar robbing lets the nectar exploiter become essentially independent of floral morphology (Stiles 1985), some behavioral attributes should be associated with this behavior. For example, Stiles (1983) observed that Fiery-throated Hummingbirds (Panterpe insignis) utilize flowers perforated by flower-piercers and may follow the flower-piercer from flower to flower, using the flower-piercers' holes to extract the nectar. This observation suggests that an inherent difference in behavior should exist between this nectar robber and a non-nectar robbing species (Brian 1957). In contrast to most hummingbirds that visit flowers by the obvious and correct entrance, nectar robbers should be expected to have a more plastic and less stereotyped set of behaviors. In contrast to most legitimate visitors, nectar robbers need to keep track of the flowers that have been punc- tured by the flower-piercers and have to deal with, for example, flowers with well-protected nectaries such as most bromeliads. This suggests that nectar robbers should differ from legitimate visitors in their tenacity and observational skills when obtaining food. Another difference between these two groups of hummingbirds is that individuals of most nectar robbers forage alone, and rarely defend territories (Wetmore 1968, ffrench 1973, Meyer de Schauensee and Phelps 1978, Stiles 1985, Hilty and Brown 1986, Stiles and Skutch 1989). Typically, nectar robbers do not establish territories, but they are notably bellicose; they are able to withstand attacks of most territorial hummingbirds (Stiles 1985, Stiles and Skutch 1989).