Never Too Old to Be a Junior Park Ranger

Blog Post by Hilary Brumberg, River Health Program Coordinator

It was a windy fall day when I joined a group of budding field researchers and nature enthusiasts to visit the Rocky Mountain National Park for the first time. As we hiked the trails, I was in constant awe of the breathtaking front-range views and the abundant wildlife, ranging from elk to butterflies to marmots to hummingbirds. But it wasn’t just the wildlife that left an impression on me.

As I was browsing the gift shop before leaving, I happened upon a Junior National Park Ranger induction ceremony that was taking place. As the middle schoolers received their badges, I could see how proud and excited they were, and imagined how happy I would have been if, at age 11, I could help protect the incredible ecosystem I had just walked through.

Flash forward, I’m at another Junior National Park Ranger induction ceremony. This time, however, the students are Costa Rican, and they are joining the Guardaparque Junior program. Modeled after the U.S. Junior National Park Ranger program, Costa Rica’s Guardaparque Juniors program teaches students to “Explore, Learn, and Protect!” national parks and reserves in Costa Rica. The program aims to form the next generation of community leaders and conservationists by educating them on the complex interactions between society and the environment. The National System of Conservation Areas (SINAC) is spearheading this pilot program with the support of local non-profits, including Osa Conservation.

Hilary teaches Guardaparque Junior students to identify macroinvertebrates, mini might-beasts whose diversity indicate river health, in the river that provides most of the water for the La Palma aqueduct system.

The first workshop for Guardaparque Juniors from La Palma High School focused on freshwater, from montane forest streams to home taps. Because freshwater conservation incorporates ecological study with social, economic and political factors, we at Osa Conservation thought it would be a good way to introduce the students to complex conversations about conservation. To illustrate how freshwater conservation affects their lives, administrators of ASADA La Palma (local aqueduct administration organization), SINAC and I took the students to the source of the stream that provides water for most of the La Palma area. I felt like a Junior Park Ranger myself as we trekked through lush old growth forest to reach where the stream fed into holding tanks and an automated chlorination system—the source of the water whenever the students turn on the taps of their kitchen sinks at home.

Guardaparque Junior students, ASADA La Palma administrators and SINAC environmental educators identify macroinvertebrates they collected from the river.


Guardaparque Junior students performed a pH test and found that the river water chemistry was neutral, which is in the healthy range.

To confirm the health of the stream, the students and I worked together to analyze the water chemistry and searched the rocks and leaf litter for macroinvertebrates, insect larvae and shrimp whose diversity indicate the health of the river. Then we followed the river downstream as it passed through cattle pasture and the bustling center of La Palma, where we repeated our mini-experiment. We found significantly lower macroinvertebrate species richness, which demonstrated how the river is adversely affected by deforestation and urbanization.

Renowned Osa botanist Reinaldo Aguilar explains that healthy forests are essential to river health because they provide nutrients, prevent erosion, regulate temperature and filters toxins.

Programs like the Guardaparques Junior and the Junior National Park Rangers are essential to nurturing the next generation of conservationists because they engage students and bring them outside. By the end of our workshop, the Guardaparque Juniors had a new perspective of how the health of the river and the health of La Palma’s residents are inextricably linked. The next time they turned on the tap, it would be with the understanding that they have a part to play in keeping their town’s water clean and preserving the health of the forest that provides it.


Mangrove Restoration Actions in the Térraba Sierpe National Wetland

Blog Post by Luis Carlos Solis, Mangrove Restoration Coordinator

The Térraba Sierpe National Wetland encompasses the largest mangrove forest in Costa Rica with an area greater than 16,000 hectares which, due to its biological importance, was declared of international importance by the International Convention on Ramsar Wetlands. In this protected area, mangrove resources have been used since pre-Columbian times when indigenous communities extracted dye from the bark of the red mangrove (Rhizophora mangle) to dye their clothing.

A section of land cleared of invasive ferns

Currently, the inhabitants of the wetland base their economy on various activities such as the extraction of the “piangua” mollusk (Anadara tuberculosa), artisanal fishing, and the isolated production of various crops and livestock; however, in the past, the local economy was based on the extraction of wood for the production of coal, firewood and construction materials, which decimated the mangrove forest. As a result of this deforestation, the “negraforra” fern (Acrostichum aureum) has dominated the wetland, which is an opportunistic species that is difficult to eradicate. Due to its high density, it acts as a barrier to the natural growth of the mangrove.

A pianguero working on planting mangroves


A pianguero in a Mangrove Nursery

As a result of this barrier in forest regeneration, Osa Conservation is carrying out mangrove restoration actions through the project “Effective strengthening of mangrove ecosystems in Costa Rica and improvement of the quality of life of the local coastal population” with funding from ALDI SÜD and KfW-DEG. Osa Conservation is pursuing this project in conjunction with the Association of Piangueros and Marine Resources of Ajuntaderas (APREMAA) in order to promote the health, integrity and sustainability of a degraded ecosystem.

The Osa Conservation Team out in the field

These restoration actions are based on active management, a technique that uses human intervention to remove the barriers that prevent the natural regeneration of the mangrove. This involves removing the fern in order create a more favorable environment for mangroves at restoration sites. The project is also establishing mangrove tree nurseries in order to accelerate the recovery processes of the ecosystem. All these tasks are carried out in conjunction by different institutions and national and international organizations such as the Osa Conservation Area, the Osa Municipality, the National University through its Applied Tropical Ecology Laboratory, Bluesensus, Shore-Rainbow Export Processing Group, ICE Group-El Diquís Hydroelectric Project, and GIZ Agency, among others.

Cutting the ferns in a restoration plot

These efforts are part of a government policy for the conservation and recovery of wetlands as a fundamental element in the sustainable development of the communities that depend on them as a way of life. For Osa Conservation, it is a privilege to be a part of these efforts and to safeguard the fundamental services the wetlands offer.

The Universidad Nacional team


The Association of Piangueros members working to plant mangroves

To find out more about our work with mangrove conservation, click here.


Building our Marine Program: Connecting in the Osa

Blog post by Mónica Espinoza Miralles, Marine Conservation Scientist

For those passionate about the underwater world it is amazing to see how extraordinarily different the seas are around the world. This was the case for us:  Noelia Hernández, an oceanographer from Spain and Osa Conservation’s new Marine Program Coordinator, and myself, Mónica Espinoza, a marine biologist from Costa Rica and Osa Conservation’s new Marine Conservation Scientist. We had the opportunity to meet for the first time at Saladero Ecolodge, and from that moment, we realized that we both have a great affinity, passion and curiosity towards the sea. For this reason, we are extremely excited to be the new members of the Marine Conservation Program at Osa Conservation, to build on the local partnerships, and to protect this unique and special marine landscape.

The experience at Saladero Ecolodge started by taking a canoe and navigating through the calm waters of Golfo Dulce. Once across this incomparable tropical fjord with a depth of around 200 meters, you can see the Piedras Blancas National Park. Saladero is located right at the foot of this protected area, a site that immediately exhibits that special interaction between the sea and the land.

Saladero EcoLodge view from the sea

When we arrived, we had the opportunity to explore the primary and secondary forests that surround this beautiful hidden corner of the South Pacific, and to suddenly find the flow of the river that crosses and bathes the beautiful lands of the tropical forest and converges in the waters of the blue sea of Golfo Dulce. That is when we decided to venture in kayaks to be one with the river, to flow through its channels and be surrounded by nature. At the mouth of the Esquinas River, we found the complex mangrove ecosystem, a place of great diversity in flora and fauna and a refuge for future generations of hammerheads, also known as the guardians of Isla del Coco.

Mangrove forest perspective from the kayak

After that wonderful experience in this important carbon sink, the desire to enter the underwater world increased. So, we took our snorkeling equipment and dove to find the submerged paradise that many seek. The world below the sea surface is a place that captivates you, takes you out of everyday life and makes you live in the present where the connection with nature is magnified. This is where we had a magical encounter with a curious hawksbill sea turtle, which seemed to stop us in time and show us how magnificent these creatures are in their own way. Sea turtles are not only beautiful animals, but also show incredible perseverance and endurance. After all, they have nested on beaches for millions of years.

Noelia exploring a hard-coral formation

At the end of our little adventure we headed back to Saladero Ecolodge completely unaware of the encounter that awaited us. In a moment of rest on the kayak, we were appreciating the horizon and suddenly we observed a splash of water in the distance. We looked at each other excitedly, and when we looked closely we could distinguish around five dorsal fins that broke the surface tension of the water; they were bottlenose dolphins. Seeing one of the resident species of marine mammals in the Golfo Dulce feeding from our kayak was nothing short of spectacular. At the end of the day, this confirmed what we had read and heard about the Golfo Dulce, a home to many species, both resident and migratory, and a key site of essential ecosystems. Such an experience only reconfirmed our excitement and dedication to helping Osa Conservation expand a Marine Conservation Program to protect these incredible habitats. We look forward to sharing more information with you in the near future about this new program.

Monica kayaking on the way back to Saladero EcoLodge after sighting bottlenose dolphins

Sometimes it is difficult to imagine the amount of life that congregates right on the coast, but after this experience in Saladero, we are extremely enthusiastic about the new opportunities that await us. Even more important is to fulfill our mission to preserve what we are so passionate about and that we now call our new home.

If you too are interested in participating in the marine exploration of the Golfo Dulce and the Osa, check out our travel package offered here—join us for a few days exploring the rainforests, the mangroves, and waters of the Golfo Dulce. We hope to see you soon!


Osa Big Day 2018

Blog Post and Photos by Patrick Newcombe

Osa Conservation’s landscape is a mosaic of terrestrial habitats including grasslands, palm forests, reforested areas, secondary and primary forests, as well as aquatic habitats such as a ponds, rivers, lagoons and ocean. Elevation ranges from sea level to 1,083 feet (330 meters). This habitat and elevation range result in phenomenal bird diversity and illustrate the importance of the habitat conservation and restoration occurring at Osa Conservation.

June 25 was the first Big Day at Osa Conservation! In birding circles, a Big Day is a twenty-four-hour time period from midnight to midnight where a team tries to identify as many species as possible by sight or sound, in compliance with the American Birding Association’s official rules. Adding to the challenge, we planned a carbon-free Big Day without motorized vehicles. We found 135 bird species despite a three-hour downpour in prime birding hours! We would love to do a Big Day again during migration to include migrating species such as warblers and shorebirds, and we feel that we could break a much higher benchmark.

The Big Day Team

Our team consists of Thomas, Zac and Patrick from Osa Conservation, as well as Henry, a local resident, and Nito, a Costa Rican birding expert and owner of Surcos Tours. The excitement mounts the evening before as we discuss strategies and plans over dinner. “What do you think a realistic goal is? …80? …90?” “What time should we look for the crested owl?” “What do you think of walking up the river?”

The alarm goes off at 3:45 a.m. and we quickly pick up Crested Owl and Common Pauraque calls around the clearing around the Biological Station. And we are off!

We walk down to Osa Verde where we bird the farm fields interspersed with hedgerows and trees along with the reforestation arboretum.


Then, we continue along the former air strip reclaimed by marsh and grassland and along the ocean before heading back down the driveway to the entrance of Osa Verde.

Here we stop to enjoy Emilie’s delicious field breakfast of gallo pinto, fried eggs, and plantain (Emilie was awake even earlier than us to prepare our field breakfasts!). It’s still not 9:00 a.m. and we have birded an amazing seventy-four species, far surpassing our expectations! Nito comments that it’s a good thing that Osa Conservation has worked so hard to conserve this land and the wide variety of habitats, allowing us to find such a wide range of species.

Ruddy-Breasted Seedeater

Our plan is to head off to the primary and secondary forest where we anticipate quickly adding many forest species. But, as birders know, the results of a Big Day are often influenced by the weather. Before entering the forest, the torrential downpour begins and we rush along the trail to reach a shelter overlooking the pond known for its “frog explosions” after rainy nights. We hang out on the platform for an hour with only a Purple Gallinule making an appearance. Although realizing that most species will be hiding quietly in the rain, we decide to head out in the downpour and, luckily, spot a Green Heron as we leave the pond area on Discovery Trail. Just before, we had hiked the second half of Discovery Trail in the morning and seen twenty-three species but, disappointingly, now the birds are in hiding.

Reaching Piro River, we find the water level has risen significantly, but we decide to stick to our plan to head up through the river to look for an occupied Band-tailed Barbthroat’s nest, staked out by Patrick and Zac the day before. Piro River raises our spirits as we also spot a Fasciated Tiger-Heron.

The rain continues steadily and we head back along Discovery Trail. When we reach the Biological Station, everyone is gathering for lunch and eagerly questioning us about the Big Day.

After lunch, we head up Tangara Trail in hopes of seeing the Spectacled Owl that Patrick and Eduardo had found on Saturday. Our hopes are also set on finding a flock. Rainforest birding is tough because we often go long distances with few birds until meeting a flock where we have to pick out as many species as possible before it moves off.

The forest is quiet except for the Scarlet Macaws and Orange-chinned Parakeets making a racket. It is not until high up Ajo Trail that we encounter our first flock. What a reward: about fifteen species, including a Gray-headed Kite, fly in.

Nito suggests heading up towards Cerra Osa in hopes of spotting some birds of prey. Cerra Osa is at 1,083 feet (330 meters) above sea-level and consists of a reforested area where the tree cover is not as dense. We are rewarded by a Northern Bentbill and White-necked Puffbird, two very unexpected species, while also finishing out our honeycreeper sweep with a Green Honeycreeper.


White-Necked Puffbird

After checking out Cerro Osa, we head back down to the research station to reassess our list. Since we usually see Amazon Kingfishers and a Ringed Kingfisher lower down Piro River, we head down to explore the river some more, quickly snagging a few more species including kingfishers as well as the Scarlet-rumped Cacique and Golden-naped Woodpecker. Night is approaching, and Nito and Henry have to return to Puerto Jimenez. Osa Conservation’s first Big Day has come to an end.

An endangered Black-Cheeked Ant Tanager

It’s been a fulfilling day. Before coming to the Osa Peninsula I had participated in some Big Days as well as the World Series of Birding and was very curious to see what we could accomplish during a Big Day on Osa Conservation’s property. One hundred and thirty-five species far surpassed my expectations. Our list can be found here. (If you’re interested, here is a description of a Big Day during the World Series of Birding in New Jersey.)

More important than the overall number, the Big Day illustrated to me the engaged and motivated community at Osa Conservation. At lunch and dinner, many people asked questions about the Big Day and the birds, often wishing us luck during our search. We worked as a team in partnership with local guides, Nito and Henry, continuing our friendship. It is the comradeship within the team and at Osa Conservation that I will remember most.

Hopefully, there will be more Big Days at Osa Conservation to illustrate its amazing bird diversity and the importance of the conservation being done.


Bird Acoustic Project: Changing their tune

Photos and Blog Post by Thomas Meinzen, Restoration and Rewilding Intern and Birder

At the Osa Conservation Biological Station, mornings in the rainforest are full of sound—birds, frogs, insects, and monkeys all chirping, singing, buzzing and howling in a unique concert. But not far away, where staff and volunteers are working to restore and rewild deforested pasture lands, the dawn chorus strikes a different tune. Many of the low whistles, creaks, and croaks of the forest are being replaced by new, often higher-pitched sounds. As a researcher and intern with Osa Conservation, I’m studying how changes in forest structure (both deforestation and regeneration) are affecting animal sounds, focusing particularly on bird acoustic communication.

Birds play important roles in forest regeneration by pollinating flowers and dispersing seeds, helping rainforest plants to colonize disturbed areas. At the Biological Station, the White-necked Jacobin (left) is a key pollinator, and the Scarlet Macaw is an important seed disperser.

Birds have key roles in pollinating and dispersing the seeds of rainforest trees, and so are an especially important group for understanding the effects of forest loss and promoting forest recovery. Deforestation can alter bird communities in surprising ways. My research tests a theory called the “acoustic adaptation hypothesis,” which proposes that birds evolve their songs with characteristics that help them travel most efficiently through particular habitats. Because low pitches, which have longer wavelengths, can bend more easily around obstructions like trees, bird species adapted to forest loss may sing higher pitches in open pastureland than birds living in intact forests.

Birds of intact forests tend to have lower-pitched vocalizations with a narrower range of pitches, which can transmit better through forest understory vegetation. Here we can see this exemplified in the spectrograms (song pictures) of two species of tanagers common on the Osa. The Gray-headed Tanager, a forest understory species, has lower-pitched calls than the Cherrie’s Tanager, a species adapted to open habitats and edge.

To test this, I will head out into the beautiful primary forest to record the wide variety of birds that live there. I will be comparing their vocalizations with those of the birds living in the neighboring grasslands, where Osa Conservation is planting trees to restore these abandoned pasturelands. This research will help show how birds may adapt acoustically to changes in habitat, examining one way in which humans are impacting the sounds of the forest. Recording natural sounds and studying bird bioacoustics offers an exciting new way to assess wildlife populations for conservation on the global biodiversity hotspot, the Osa Peninsula.

Intern Thomas Meinzen in the field



Rare Encounters: Finding the Wrinkle-face Bat

Blogpost by Manuel Sanchez, Sea Turtle Program Coordinator and Wildlife Photographer

There are more than 114 species of bats, and around 80 of these can be found in the Osa Peninsula. Some are so common that they practically live in our houses, while others are so difficult to spot that when you encounter one, you are caught off guard and can’t help but think that no animal more incredible exists. It is said that the Osa contains more species of bats than the rest of Costa Rica, and I believe it to be true, because it has the best sites and resources. If I were a bat, I would of course choose to stay in the Osa.

I have had the opportunity to hold a bat in my hands, and to have helped on many investigations to identify bats and attempt to understand their ecology. I have been familiar with bats since I was a kid, ever since I had an encounter with a vampire bat. In reality, my mother was more scared than I was at the time…

A close up of a wrinkle-face bat; Photo by Manuel Snachez

But the bat that has always had my attention is called the wrinkle-face bat, or the “old bat.” One night I was working late at Osa Conservation Biological Station. It had rained for the first two hours of the night, and typically after such a rain many animals come out, especially the bats. Walking the coyunda river toward my house, there is a guava branch about three meters above the water. While searching for snakes and frogs there with my flashlight, I saw two eyes that didn’t belong to a frog, much less a snake. I approached very slowly as to not scare the animal, but in truth I was more scared of it than it was of me. I stayed with the bat for what felt like hours, watching how it ate a fichus fruit. It was a truly incredible experience: to think we have such beautiful and surprising animals in the Osa! I couldn’t wait for the excitement of successfully identifying the species, and I returned to the station to ask bat researcher Gloriana Chaverri, who happened to be staying with us at the time. Of course, she already knew the species from her years of work with bats. That was the only night I have seen the wrinkle-face bat in this giant forest, but the Osa continues to surprise me every day!


National Jaguar Initiative

Blog Post by Juan Carlos Cruz Díaz, Feline Program Coordinator

When we talk about the jaguar, it is difficult to distinguish the many vital roles this iconic species plays. All throughout Latin America, the jaguar is deeply rooted in the indigenous culture. From a cultural point of view, it has been part of many artistic and cinematic works. From a conservationist point of view, it has been considered everything that a species can be: an umbrella species, a flagship species, a keystone species, an indicator species, and an apex predator.

In spite of its huge importance, however, we know very little about the species’ ecology and what is necessary for its conservation.

Due to the jaguar’s biological characteristics, research techniques necessitate much physical, economic, and logistical effort, and thus, it is no easy task to study them. However, when these efforts are realized, every result is significant and further augments our knowledge of biology and ecology.

This year in Costa Rica, Osa Conservation worked with partners to analyze the results of the first national jaguar initiative, which brought together jaguar researchers and studies throughout the country to synthesize what we know about this important species at the national level.

The larger initiative is called: “Jaguar conservation in Costa Rica throughout the integration of species registration data and habitat modeling.” It is a product of the Promotion of Participative Management for Biodiversity Project, led by the National System of Conservation Areas and the Japanese Agency of International Cooperation with the collaboration of Costa Rican jaguar researchers.

In over a year of gathering information from diverse jaguar studies (including research from camera traps, excrement studies, road presence, sightings, records of predation of cattle and sea turtles, tracking collars, and genetic material provided through excrement), meetings, seminars, map creations, and expert consultations, the initiative obtained results that widen our knowledge of the state of jaguar conservation.

An essential part of this initiative was being able to describe the current distribution of the species and modeling ideal habitat conditions, which established guidelines for determining conservation priorities for this endangered species going forward.

Utilizing current species distribution registries and variables (habitat, human impact, and climate) chosen by experts, the initiative predicted suitable habitats for the species throughout the continental territory of Costa Rica.

Map predicting suitable habitats for jaguars in Costa Rica.

Zones were identified with the best habitat conditions for the jaguar. They were delineated as focal areas with the principal objective being to evaluate the availability and characteristics of existing biological corridors at the national level in order to connect these areas.

The focal areas identified are located largely in the Talamanca Caribe and Amistad-Pacifico region, the Caribe-Norte, the Osa, and the Cuanacasta and Volcanic Mountain Ranges.

The findings of this study represent recent knowledge about the distribution of the species and its ideal habitats, based on registries of presence/absence, relying on the participation and evaluation of national and international experts studying the species. Bringing together this diverse array of studies and researchers is unprecedented in Costa Rica. It constitutes the starting point for developing a strategy that prioritizes medium-term conservation efforts for the sake of obtaining a better and more efficient response to the conservation needs of the species, based on biologically and scientifically supported information.


Restoring Mangroves & Managing the Mangrove Fern

Blogpost written by Luis Carlos Solis, Technical Assistant

The mangrove fern, an opportunist in disturbed environments

Mangroves are one of the most threatened ecosystems in the world. Unfortunately, mangroves in Costa Rica are no exception –  every day, mangroves around the country are devastated due to human activity, despite being declared protected areas . There are more than 80 protected mangroves identified in Costa Rica, representing approximately 41,002 hectares (101 318 acres), of which 99% are located in the Pacific. Just north of the Osa,  Térraba Sierpe National Wetland stands out as the most extensive mangrove in the country, with an area greater than 16,000 hectares (39 537 acres) – representing almost 40% of the mangroves reported for the entire country!

Terraba- Sierpe Wetland

Terraba- Sierpe Wetland from above by Frank Uhlig


The Térraba Sierpe National Wetland was declared internationally important  in 1995 by the International Convention on Ramsar Wetlands and through the Costa Rican Forestry Law. Through this designation, it became prohibited to cut or exploit the timber resources of this ecosystem. Prior to this in the 1970’s, timber was legally extracted in this area for the production of coal, firewood and construction materials, as well as bark for tannins and molluscs. This, combined with a large illegal extraction decimated much of this valuable mangrove forest.

In the 1980’s, the extraction and use of wood products from Térraba Sierpe Wetland led to a massive establishment of the mangrove fern Acrostichum aureum –  a native species that has a tendency to become overabundant with lots of light. In a healthy mangrove ecosystem, this mangrove fern coexists and is regulated by the shade of the large mangrove trees.  However, once mangrove trees are cut, the fern takes advantage of the light and space and becomes difficult to eradicate. High densities of this fern then prevent smaller mangrove saplings to grow and to establish healthy mangrove trees. Thus, in order to restore the mangrove ecosystem back to a more natural state, active restoration strategies must include removal of this aggressive fern.


mangrove fern

Mangrove fern is regulated by mangrove trees. In a healthy ecosystem, the fern is more easily managed and lives in balance.


mangrove fern

Without the presence of mangrove trees, the mangrove fern takes over. As an opportunistic species, this fern becomes overly abundant and grows very tall.


As Osa Conservation has been committed to protecting and restoring the Térraba Sierpe National Wetland, we plan to restore 50 hectares (20 acres) of mangroves that are currently occupied by the Acrostichum fern. As part of our new project called “Effective Strengthening of Mangrove Ecosystems in Costa Rica (Terraba Sierpe) and Improvement of the Quality of Life of the Local Coastal Population,” we aim to restore the structure and functions of this important mangrove ecosystem and help empower local communities  to responsibly manage the non-timber resources offered by the mangrove.

We had a wonderful time recently celebrating this project. Working a with a wonderful group of partners, we are grateful to all of the participants who came out to support the project and we look forward to continuing to collaborate on this important effort to protect and restore this vital ecosystem.




Rewilding Ants: Conserving Endangered Interactions

Blog by Ruthmery Pillco Huarcaya, Botanical Projects Coordinator
(Translated by Amaris Norwood, DC office intern)  

One of Osa Conservation’s objectives is to support the conservation of at-risk trees through the conservation ex-situ program  (such as the creation of a botanical garden) which is a supplement of the in-situ ecological restoration and rewilding program that we continue to pursue.

About the Cornizuelo

It has been more than a year since we planted the seeds of a Vachellia allenii tree, locally known as a cornizuelo (the tree of the horns).  This tree can be found growing abundantly in both primary and secondary forests and can reach heights of 25 meters. The cornizuelo, characterized by spines that grow in twos, looks like a pair of horns. This species is endemic to Costa Rica and is categorized as endangered (EN) by the International Union for the Conservation of Nature (IUCN). Its greatest risk is the loss of habitat, which is a common consequence of deforestation.  

 Arbol de cornizuelo (Vachellia allenii) creciendo en un bosque protegido (Saladero Ecolodge)

Cornizuelo tree (Vachellia allenii) growing in a protected forest (Saladero Ecolodge)

The Relationship Between The Tree and Ants

The tree coexists with a specific species of ant, the Pseudomyrmex sp., with whom it has established a very special relationship.  In this case, the cornizuelo brings refuge and food to the ants and their offspring. The large, hollow spines grow to become an ideal site for the ants to live, reproduce, and feed. The plant produces small, yellow bodies containing sugar and proteins that serve as abundant and delicious food sources.   

Hoja de un cornizuelo mostrando los cuerpos alimenticios que produce ara alimentar a sus hormigas (foliolulos modificados de color amarillo)

Cornizuelo leaves showing the alimentary bodies that produces ara to feed ants (modified yellow leaflets)

The ant by its part protects its host plant against the attack of herbivores, particularly insects, and further prevents other plants from becoming its competitors for sunlight, space, and nutrients.  When something touches the plant, hundreds of furious ants appear, dispersing to protect the plant from intruders. The
 furious ants produce a free space of vegetation around the cornizuelo by using their jaws to cut vines and eating seeds and seedlings that attempt to grow around them.  Living together has become a matter of survival as much for the plant as for the ants.

Our Rewilding Efforts

Over the course of 9 months, we noticed that our cornizuelos did not develop. They hadn’t been colonized by ants, and possibly, were never colonized. Such was the case with a cornizuelo we planted in the station after throwing away the previous flowers. We then undertook a trip through Saladeros Ecolodge in the National Park of Piedras Blancas, where we found an area with many cornizuelos. As a first attempt, we decided to bring a sample of a seedling with all of its ants.


Newly colonized cornice seedling. The horn-shaped spines show a hole recently made by an ant (Pseudomyrmex sp.).


One time in the nursery, we collected the plant with ants besides our cornizuelos. The ants immediately started to explore and eat from the yellow bodies.  After a few hours, they started to make holes in the thorns, and on the following day, all of the thorns had holes. Our cornizuelos started to grow rapidly, looking vigorous and filled with life.  However, the ants disappeared in a month, probably due to the absence of a queen ant, or because the ants got lost while leaving to explore.

When you destroy a forest, you also destroy the mutualistic interactions between plants and animals that have spent hundreds of years developing. These interactions are very delicate and are difficult to recuperate and restore.  Though our first attempt at rewilding this interaction did not do as well as we hoped, we continue to do more research so that the cornizuelos and their ants stay together.


Data Entry Company India


Ruth monitoring the newly colonized Cornizuelo seedlings



Blog Post by Marina Garrido, Restoration Research Field Assistant


Growing Trees in the Osa’s Forest Floor. Photo by Frank Uhlig

Recent Restoration Success at Osa Conservation

Over the past months, the Osa Verde Restoration Plots have been the liveliest place on our property. Wondering why? During this time, we have worked and successfully planted 14,000 trees! A large hard-working team is behind this incredible project. But one of the main pillars of our restoration success is Agustin Mendoza.  

Saplings in our Tree Nursery. Photo by Frank Uhlig

Agustin Mendoza has worked for Osa Conservation for 8 years as our reforestation manager. One of his roles is to collect the seeds that will make up our future forests. But this is not always an easy task. To collect a biodiverse range of seeds, he must gather them from all levels of the tropical rainforest.  This requires climbing trees to collect those hard to find seeds. Once gathered, he plants the seeds and cares for them until the saplings are strong and healthy.

A Conversation with Agustin Mendoza

Early Experiences with Forest Restoration

Variety of Trees, in Age and Size. Photo by Frank Uhlig

Agustin is someone I  have been amazed by since I joined the Osa Conservation family. Every time I talk with him, I learn something new about Osa’s forests. Thus, I couldn’t resist joining him for a cup of coffee:

  • When did you become interested in reforestation?

I was very young, when I was just seven years old. My father taught me how to plant and take care of trees. I used to plant different native fruiting tree species on my family’s farm. This is when I realized how beautiful and rewarding it was to plant a tree and watch it grow.

  • Your passion for reforestation started at a very young age: How did you come to join the Osa Conservation team?

Before Osa Conservation, I worked on reforesting Cerro Osa for the founder of Osa Conservation; Adrian Forsyth. Then I started working on every reforestation project I could, planting different native tree species across the Osa. One project took to another and then I began to lead the reforestation efforts at Osa Conservation. The first trees I planted for Osa Conservation are currently 30-40 meters tall.

Looking Forward

Diverse Species of Trees in the Osa. Photo by Frank Uhlig

Diverse Species Growing to Build the Canopy. Photo by Frank Uhlig


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  • This year, the reforestation project has taken on an innovative project with the balsa experiment. What do you think about this project? Do you like the idea of focusing restoration efforts on an experiment in hopes of future reforestation successes? 

    Augustin Mendoza with a Balsa Sapling.

    Augustin Mendoza with a Balsa Sapling.

I like it a lot.  I love the idea of trying new ways to speed up forest recovery and bringing back the ecological interactions you would normally find in a healthy forest. Also, with the species we have planted, they will require more care, and there is nothing I would love more than to help these little trees grow.

  • Do you have a particular project you would like to accomplish in the future?

I would love to share my knowledge with more local people. Give them seeds and show them how to grow them so they can reforest their farms.                                                                Then, everyone will see how beautiful reforestation is.

  • Would you like to send a message to everyone who is reading this?

Take care of the forest, it is our responsibility to protect it. The forest gives us everything we need without us asking; in exchange, we have to help, for nature’s well-being and our own. It’s easy, we just need to take the step and be conscious of our actions.

A Young Spider Monkey Exploring the Dense Forest of the Osa; Photo by Frank Uhlig

A Young Spider Monkey Exploring the Dense Forest of the Osa; Photo by Frank Uhlig