By:

Monteverde Institute Interns (2022): Garrett Higgins, Jordan Slayden, and Annie Hageman

Roberto Vargas, Bioacoustic Sound Researcher, University for Peace, UNED

Debra Hamilton, Principal Investigator, Monteverde Institute Research Affiliate

The Central American endemic Three-wattled Bellbird (Procnias tricarunculatus; hereafter bellbird) is a promiscuous, migratory frugivore. Currently listed as “Vulnerable” on the IUCN Red List, bellbirds travel to the Monteverde region to follow the fruiting of trees in the Lauraceae family. Their migration cycle brings them from the Caribbean region of southeastern Nicaragua to the Pacific coast of Costa Rica, to the Atlantic Slope of the Tilarán Mountains, and across the continental divide to the cliff edge region of Monteverde during their breeding and post-reproduction season (Powell & Bjork 2004). In Monteverde, males claim and defend territories by calling three to four times a minute for most of the daylight hours with blaring calls that can be heard extensively from distinct high or under-canopy perches.

Not only do bellbirds play a crucial role in their ecosystem as key seed dispersers of wild avocados, but they also help to support Monteverde’s community. In 2005, 28% of the area’s annual income from tourism was derived from ecotourists arriving to see quetzals and bellbirds, totaling approximately $17,539,200 (Allen et al. 2008).

Past research

Since Barbara Snow’s groundbreaking study in 1974, there has been a rich history of bellbird research in the Monteverde region (Snow 1977). Local researchers George Powell and Michael Fogden first perceived a decline in bellbird calls near the Monteverde Cloud Forest Preserve in the late 1980’s. Powell, a key leader of conservation in the Monteverde zone, formed the first bellbird investigative group including Carlos Guindon, Robin Bjork, Vicente Espinoza, Danilo Brenes, Debra Hamilton, Victorino Molina, Koki Porras, Pedro Bosques, and volunteers. They sought to learn about the bellbird’s local habitat use and migration patterns. Carlos Guindon documented bellbird activity throughout forests of the region to show the importance of these fragmented habitats in a mosaic of farmland (C. Guindon dissertation).

In 1997, Hamilton, Molina, Bosques, and Powell completed a thorough investigation of the species’ status in Costa Rica and Panama (Hamilton et al. 2003) and concluded that the lack of habitat on the Pacific slopes of both countries was the cause of the bird’s decline. This finding led to the formation of the Fundación Conservacionista Costarricense in 1998, an organization that protects and restores habitat. Organized censuses (Figure 1) were led by the team and carried out with the collaboration of interns (McCullogh, Duca, Hageman, Higgins, and Slayden: 2013, 2016, 2022), guides from the Asociación de Guias de Monteverde (Table 1 -1997-2010), and volunteers. The Tropical Science Center and Unión de Ornitólogos have regional census data post 2010 which was not incorporated into this study but merits attention regarding long-term population trends. Hamilton, Rhine Singleton, and J. Deveraux Joslin further investigated the tracking of fruit resources for the bellbird in a six-year study and concluded that no single species of tree provides sufficient forage consistently for bellbirds since these species don’t produce fruit each year (Hamilton et al. 2018). Four of the more than 36 fruits eaten by the bellbirds during the months of June to August are of special importance: Ocotea monteverdensis, O. floribunda, Damburneya salicina, and Myrsianthes “black fruit”.

Figure 1. Results of annual bellbird census, Monteverde (see participant list in Appendix A).

2022 Research

We researched bellbirds from May to August in the Monteverde region to document male bellbird territories and to analyze patterns and longevity of site use. We compared our findings to those sites documented by Barbara Snow (1974 results) and the censuses of 1997-2010. Using standardized census methods that followed the previous work, we surveyed four routes amounting to 12 transects in the upper Monteverde sector (11.5 km2) that included the Snow study area (underestimated in her article, we believe, as 5 km2). We recorded visual and auditory observations of individual bellbirds, including sex, age (adult, juvenile, or immature), percentage of adult plumage, calls per minute, dialect, presence of bands, perch height, and behavior. We analyzed the full collection of census data to discern patterns in bellbird use of transect area, determine territory locations, and study the staging of adult and non-adult bellbirds from April to July in order to define post-reproductive shifts in habitat use and territory infringement. We described known territories using a variety of detailed physical measurements including territory area, topographic information, forest strata, fruit availability, and perch characteristics. These measurements confirmed many of Barbara Snow’s territory descriptions from 1974 and added further detail.

We conducted three behavioral studies at three known territories for approximately four continuous hours each where we noted perch changes, calls, interactions, and other behaviors. In addition, the research team utilized bioacoustics to better understand the impact of bellbird auditory boundaries and the role they play in holding territories. We recorded audio of four individual calling bellbirds using a Zoom H5 recorder with a directional capsule and windshield at 0, 20, 100, 200, and 300 m from the advertising perch. We then analyzed the recordings using Raven Sound Analysis to obtain the approximated maximum distance bellbird calls (both Talamancan and Monteverde dialects) carry in forested and open landscapes.

Results of the 2022 Research

In total, we confirmed 19 actively held territories in the approximately 11.5 km2 study area in the southwestern end of Monteverde (Figure 2). We confirmed previous evidence that eight territories have been occupied since 1974 (>48 years!) and an additional nine bellbird territories have been in use since at least 1999, when they were first documented in the 1997-1999 census work. At least five territories have been abandoned since 1997 or 2010.

The size of this study was restricted for comparison purposes with Snow’s 1974 work. We believe that there are several more territories that merit further study in this region, as well in other sectors of Monteverde, which we plan to revisit in 2023.

Figure 2. Map depicting Three-Wattled Bellbird territories in the Monteverde Region.

The March-May season is followed by an intense post-reproduction period where juveniles and non-territory holding males exert enormous challenges to territory holding males. This activity may serve as a key training opportunity for immature bellbird calling, elaborate territory defense routines, as well as dialect establishment. For promiscuous and lekking bird species, post-reproductive behavior may provide important insights regarding their reproductive strategies and the corresponding conservation measures to direct appropriate habitat restoration, linkages, and protections.

We are reporting our findings and those of almost 30 years of research. The 2023 season will provide the opportunity to finalize this work by answering the few specific questions that remain unanswered. We look forward to sending our next report.

Literature Cited (articles available at the MVI digital library or by request to debrahamiltonmv@gmail.com)

Allen, B., L. Lines, D. Hamilton. 2008. The economic importance of extending habitat protection beyond park boundaries: a case study from Costa Rica. The George Wright Forum, Vol .25, No. 1: 30-35.

Guindon, C. 1997. The importance of forest fragments to the maintenance of regional

biodiversity surrounding a tropical montane reserve, Costa Rica. PhD Dissertation, Yale

University, New Haven, Connecticut.

Hamilton, D., V. Molina, P.Bosques and G. Powell. 2003. El estatus del pájaro campana (Procnias tricarunculata): Un ave en peligro de extinción Zeledonia 7: 15-24.

Hamilton, D., R. Singleton, and J.D. Joslin. 2018. Resource tracking and its conservation implications for an obligate frugivore (Procnias tricarunculatus, the tree-wattled bellbird). Biotropica. 1-11 2018 DOI: 10.1111/btp.12502

Kroodsma, D., D. Hamilton, J. Sanchez, B.Byers, G.Fandino, D.Stemple, J.Trainor, G.Powell. 2012. Behavioral evidence for song learning in the Suboscine bellbirds (Procnias spp.; Cotingidae). Wilson Journal of Ornithology 125: 1-14. DOI: 10.2307/41932830 *Edward’s Prize 2013

Powell G.V.N., Bjork, R.D. 2004. Habitat Linkages and the Conservation of Tropical Biodiversity as Indicated by Seasonal migration of Three-wattled bellbirds. Conservation Biology 18:500-509.

Saranathan V., D. Hamilton, G.V.N. Powell, D. Kroodsma, R. Prum. 2007. Genetic evidence supports song learning in the three-wattled bellbird Procnias tricarunculata (Cotingidae). Molecular Ecology. DOI:10.1111/j.1365-294X.2007.03415.x

Appendix A. List of bellbird census workers 1997 – 2009

Three-wattled Bellbirds (Procnias tricarunculatus): Research Updates