Solitary sandpiper (Tringa solitaria) unlike other sandpipers and other migratory birds, do not migrate in large flocks and can be found along the banks of shady creeks. PC: Alex Wiebe

Movement is an essential part of our day-to-day lives. However, this is not only true for us; most species are constant on the move. For some, this is due to continuous changes in their surroundings and others because of their ecology. Most of these movements go unnoticed by us, however, there is one that does not: Bird migration. If you look up into the sky at this time of the year, you may notice the unusually high number of birds flying around. For birds that migrate, they do so twice a year, between their breeding homes habitats and their nonbreeding grounds. Some migrations are large-scale like the Artic tern (Sterna paradisaea) which incredibly manages an annual round-trip of 70 000 km. Others are much shorter, such as altitudinal gradient migration along the Andes.

Migration is the seasonal movement from one region to another influenced by a series of factors. Specifically, bird migration is strongly influenced by the availability of nesting sites and food. In temperate zones, the hours of increased light during the summer allows birds to forage for longer periods. Additionally, because of the lower biodiversity, competition for resources and nesting sites is not as intense. These are appealing conditions to use temperate zones as breeding sites. Yet, as the season ends, food availability and the hours of light decrease, and birds have to find suitable grounds for the rest of the year. The tropics, despite the food abundance throughout the year, are not attractive to some species as breeding grounds because of the intense competition for resources and nesting sites due to the great biodiversity. However, most of these species become temporary residents of the tropics until is time to breed again.

Out of all the bird species in the world 40%, or around 4 000, are regular migrants. However, they are unevenly distributed around the world. In countries in the far north like Canada and Scandinavia, birds migrate southwards during the boreal winter to flee the harsh winter and will only go back until the following spring.

Chivi Vireo  (Vireo chivi) is one of the most widespread and common passerines of South America. This species consists of a complex mosaic of resident and migratory populations. During the austral and boreal winter, there is a seasonal overlap between the resident population and wintering population from the temperate zones.  PC: Alex Wiebe

Migration can take several weeks. Because of this, birds enter a state called hyperphagia before their journey. During this state, they will ingest as much food as possible to build up the fat reserves that will provide them with the energy needed for their journey. Once the migration has started, birds use a combination of senses and cues that are not fully understood, to reach their destination. They can orientate themselves by sensing the Earth´s magnetic field, and by the position of the sun, stars, and landmarks seen during the day. Species do not migrate all at once or in the same way. This is why you can see migrating flocks or individuals at different times of the day and for several months. Each species starts its migration at a specific time and some vary their migration year to year depending on food availability. The beginning of migration is also influenced by changes in the length of daylight. First-time migrators often make the journey on their own, despite the fact that they have never been to their winter home before. Impressively they are able to find them.

To avoid exhaustion and starvation during the thousands of kilometers flight, birds stop to recharge their energy along the way. However, by doing so, they are vulnerable to fall victim to predators. While enduring their journey, migratory birds face further threats like wildfires and storms, which appear to be intensifying due to our changing climate; shortages of resting areas, due to human encroachment; disorientation by city lights; and obstacles such as tall buildings. In 1971, The Ramsar Convention on wetland was agreed as a measure to protect migratory birds. However, each year the population of migratory birds decreases due to habitat loss and degradation in the tropics. By protecting the tropical forests, we are ensuring the well-being of migratory birds and ensure that future generations have the opportunity to this spectacle.

For further reading:

• Salewski, V. & Bruderer, B. (2007) The evolution of bird migration-a synthesis. Naturwissenschaften 94:268-279.
• Robbins, C., Sauer, J., Greenberg, R. and Droege, S. (1989) Population declines in North American birds that migrate to the neotropics. Population Biology Vol. 86, pp. 7658-7662.

Bluish-fronted jacamar (Galbula cyanescens) located in bamboo at LABO. PC: Tom Matia

At the time of my encounter, I did not realize the rarity of the event. I was walking across an old channel of the Los Amigos River that is in its early successional stages. There are no tall trees, instead, there are many shrubs covered in vines. Bordering this channel are the towering trees of the floodplain forest, making this edge habitat an ideal location for a Tiny hawk (Accipiter superciliosus) (Global Raptor). I had just walked past a resting bluish-fronted jacamar (Galbula cyanescens) when my eye caught a glimpse of a bird careening through the vegetation. I followed the shadow through the vegetation and, in the clearing that the trail made behind me, watched a small flying raptor raise its feet forward and pin the bluish-fronted jacamar to its perch.

A photo taken through binoculars of the Tiny Hawk after pinning the jacamar to its perch. PC: Tom Matia

The small raptor (22-28cm/8-11in) is known to be a specialist at predating on avifauna and had the jacamar in its grip (Global Raptor). It seemed the attack would prove fatal as there was hardly a fight from the jacamar. The hawk soon took notice of my presence and, not wanting to disrupt its natural behavior and its success, I walked away from the scene. A few hours passed by the time I returned to investigate the scene; there was not a feather or scrap to be found. This could mean two things, the jacamar made it out the talons of the tiny hawk, however, due to the elongated nature of their talons, I choose to believe that the later, the jacamar left the scene in the grasp of the hawk.

When I returned to eat dinner, I learned that little is known about this species of raptor and that the sighting was very rare! Looking further into this species, I discovered that there is hardly any information on their populations. With the help of citizen science, specifically from eBird by Cornell University, I found that only 130 observations have been recorded in Peru over the past ten years. With such little documentation on this uncommon bird, it is alarming that they are estimated to lose 19-24% of suitable habitat in the next twenty-two years (BirdLife).

The Tiny hawk has an assumed population of 670-6,700 individuals and is currently listed as ‘least concern’ by the IUCN, and BirdLife, due to its expansive range (BirdLife). Hearing these statistics shocked me and I immediately searched population sizes of species that are rare to see. The jaguar (Panthera onca), an animal that is incredibly elusive, yet possibly more likely to be encountered, has roughly 15,000 individuals according to the WWF (Quigley). And so I thought, “a tiny hawk is not something you see every day”.

References:

Global Raptor Information Network. 2018. Species account: Tiny Hawk Accipiter superciliosus. Downloaded from http://www.globalraptors.org on 15 Sep. 2018
BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/09/2018.
Quigley, H., Foster, R., Petracca, L., Payan, E., Salom, R. & Harmsen, B. 2017. Panthera onca(errata version published in 2018). The IUCN Red List of Threatened Species 2017. Downloaded on 15 September 2018.

If you find yourself in the rainforest, it is almost impossible to miss the endless organized columns that army ants form. This group of ants are carnivorous and forage in swarms, raiding everything in their way. If you are not fast enough, you will fall prey to these voracious predators no matter how big you are. If you do outrun them, there are different predators waiting to trap you. Even if you are not an expert birder you probably have heard of Antbirds. This insectivorous group of birds belongs to the family Formicariidae and forage by following army ants. Eciton burchelli and less often Labidus praedator are the species of army ants that Antbirds follow. As simple as this may seem, the relationship is more complex than it sounds, as not all Antbirds are obliged to follow ants.

Hairy-crested Antbird (Rhegmatorhina melanosticta) perched above an army ant swarm | Photo by Will Sweet

This foraging behavior has no counterpart outside the tropics but within them, you can find ant-followers in different altitudes and elevations. Different species attend the raids with different frequencies. The species that regularly attend them and that in some cases depend entirely on the raiding to find their food are known as obligate, or true, Antbirds. A different name is given to the birds that follow the swarms but are also capable of foraging independently of them, they are referred to as regular followers. Lastly are the opportunistic followers, the species that are only seen foraging when the swarm crosses their territory, for which up to 70 species have been identified. In this grouping, there are some non-insectivorous species that opportunistically take advantage of the raid.

Obligate Antbirds, exclusively found in the Amazon region, are limited to the family Thamnophilidae, also known as typical Antbirds. 16 species have been recorded that completely depend on army ant swarms. They depend on army ant raiding swarms to such a degree that in patches of isolated forest where army ants disappear, the Antbirds are gone within a short period of time.  The hairy-crested Antbird (Rhegmatorhina melanosticta), a not easily seen Los Amigos resident, is an example of an obligate Antbird that depends solely on army ants year-round and can be seen in Terra Firme perching low to the ground feasting at the army ants expense.

Following the raids can provide more food than one individual can eat. But for obligate Antbirds, having developed such specialized foraging behavior has its shortcoming. The frequency, abundance, and distance away from their meals depend on the life cycle of army ants. Their life cycle alternates between periods of mobility and stillness, which makes their presence and location in a forest patch unpredictable. Due to army ants’ mobility, their nests are not as you may imagine. They don’t build a nest to live in; rather they sleep in bivouacs. Bivouacs are living ball-shaped nest made out of the workers that protect the queen and her brood.  They alternate between periods of low food ingestion needs and periods of activity every three-weeks, raiding to meet the food requirements of newly born larvae Because of the periods of ants’ stillness, obligate Antbirds have to wander off outside their home range looking for swarms to follow, as a result, they haven’t developed a strict territorial behaviour. In this case, evolution has favored birders; within a swarm raid you can observe several individuals of the same and different species. Make notice that individuals will defend their place along the raid, the closer to the front and the center they get the better the prey they could trap.

If you’re interested in birds, the next time you come to the tropics you might want to go for an early hike and look for the columns of army ants. If you wait patiently, you will be amazed by one of the greatest performances in the rainforest and see several species of highly adapted birds along the way.

In 2018, four exceptional students and/or professionals were chosen as our Franzen Fellows.  Jointly, their passion for birds has led them to pursue work in the Amazon rainforest in order to protect this great frontier.  Currently, the Los Amigos Bird Observatory (LABO) is hosting two of its fellows, Alex Wiebe and Will Sweet.  In this post we will become acquainted with the work that these two are doing and their achievements along the way.

Will Sweet arrived to LABO on May 17^th, 2018, and got right to work.  He is examining how different stages of succession around oxbow lakes impact the avifauna communities in the Los Amigos Conservation Concession. To avoid waiting for succession to unfold in real-time, Sweet has set up an observation pattern around three oxbow lakes that are already in different successional phases, from relatively new to almost totally grown over. He conducts point counts along these lakes to assess which birds inhabit which successional level.  In his pursuit, Will strives to understand the contribution of oxbow lakes to the Amazon basins’ high bird diversity, furthering our knowledge of changing landscapes’ effect on avian diversity. Will aims to attend a graduate program next fall while continuing to pursue his passion for birds.

Will Sweet conducting his morning point counts at Cocho Raya | Photo by Zander Nassikas

Finishing his last year of undergraduate studies at Cornell University, Alex Wiebe is spending his summer collecting data on one of the least understood family of birds: tinamous. They are secretive and skittish, which makes them difficult study subjects. Wiebe’s interest in patterns of avian geographic distribution in the Amazon, as well as the factors that affect their distributions, has led him to Los Amigos.  Tinamous are a natural choice for Wiebe’s work. They reach their highest density in the area around Los Amigos with 11 out of the 47 species represented, and since little is known about them, his work stands to have impact. Wiebe will be using his background in statistics to create a spatial distribution model of the tinamous of LABO and across South America. In order to collect his data, Wiebe conducts point counts in a variety of terrestrial habitats, while also recording the locations of rare species as they are heard.  With his results he will build a better understanding of this enigmatic family of birds.

Alex and Will have had an incredible summer thus far and have reached numerous achievements along the way.  Recently, Alex broke the world record for an on-foot Big Day with 347 species. A Big Day is a competitive birding ‘race,’ in which the contestant attempts to see or hear as many different bird species as they can in one 24-hour period. And Will was able to identify a species that is new to LABO: the rusty-margined flycatcher. The work that is being completed by these two fellows will undoubtedly help conserve the Amazon rainforest and the avian species that call it home.

Normally when you go out looking for birds, you look for the most colorful ones, or listen for those with the most beautiful songs. We often forget that cryptic birds have a beauty of their own. Vultures are not terribly eye-catching but they serve an important role in the ecosystem as the clean-up crew.

Vultures are scavengers, which means they eat dead meat. They are more efficient at finding carrion compared to other scavengers. You can see them soaring all around in their search for food. Their soaring behavior takes advantage of thermals, air currents warmed by the sun that allows them to reach great altitudes without beating their wings. Once they have found their meal, their extremely acidic stomach destroys any bacteria or viruses established in the carrion. This prevents diseases from proliferating and spreading to other animals and humans. Don’t think that because they are the ecosystem cleaners they are dirty birds; on the contrary, their featherless heads are an adaptation to stay clean while eating.

Turkey Vulture (Cathartes aura) soaring around in search of food. | Photo by Alex Wiebe

Although the many species of vultures all over the world serve the same role and have similar appearances, they are divided into two unrelated guilds: The Old World Vultures (Accipitridae) and The New World Vultures (Cathartidae). Los Amigos is home to four of the seven species in the Cathartidae family. The Black Vulture (Coragyps atratus), Turkey Vulture (Cathartes aura) and King Vulture (Sarcoramphus papa) are widely distributed in tropical forests, open savannahs, and grassland, while the Greater Yellow-headed Vulture (Cathartes melambrotus) is restricted to tropical forests. These four species are often seen interacting during lunchtime.

Due to their highly developed olfactory sense, finding carrion is easy for the Turkey and Greater Yellow-headed vultures. They can find their meal as early as an hour after it has been disposed. You may think that this gives them an enormous advantage over our other vulture residents, but the King and Black Vulture have found a way of benefiting from their neighbors’ awesome sense of smell. Since they themselves cannot track carcasses through their smell, they rely on reaching altitudes of 100 feet or more to be able to follow the Turkey and the Greater Yellow-headed vultures to the food source. This behavior is especially apparent in undisturbed forests where the latter is solely responsible for locating carrion and serving as a guide for the other species. This could be due to an even more developed sense of smell than the Turkey vulture or because its wing structure allows them to maneuver better over the tree canopy.

The Black Vulture (Coragyps atratus) waiting for its neighbors to find the meal. | Photo by Alex Wiebe

But what happens when all these species come together for lunchtime? Although a dominance hierarchy between species does exist, most of the time there is not a direct aggression between them. The interaction could result in different species feeding at the same time from the same resource or in individuals leaving when a more dominant species is approaching. More intense aggression has been identified between individuals of the same species. Furthermore, the differences between species in size and bill length and the postures they adopt while eating could be a factor allowing the presence of more than one species at a time. These differences enable them to forage from different tissues of the carcass simultaneously, which may reduce direct competition.

Close to Los Amigos, the main threats that vultures seem to face are the misperception of people. People believe they attack their cattle ranch or that they are dirty birds. But as described here, they feed on dead meat and they even prevent diseases from spreading. Despite their unattractive appearances, vultures are interesting and important birds in our ecosystem. Here at Los Amigos we are excited to have this array of species taking care of the health of our forest.

If you see the King Vulture (Sarcoramphus papa) and Greater Yellow-headed Vulture (Cathartes melambrotus) from far, you can tell them apart based on the color of their breast plumage. | Photos by Alex Wiebe

For more references:

• Gomez, L.G., Houston, D. C., Cotton, P. and Tye, A. 2008. The role of Greater Yellow-headed Vultures Cathartes melambrotus as scavengers in neotropical forest. IBIS Journal 136: 193-196
• Houston, D.C. 1987. Competition for food between Neotropical vultures in forest. IBIS Journal 130: 402-417