Panamanian Cloud Forest Hummingbirds

During the Fall of 2022, I attended a semester program in Tropical Ecology, Marine Ecosystems, and Biodiversity Conservation through the School for International Training (SIT) in Panama. At the end of this program, we were able to spend a month conducting independent research on any topic we wanted. I chose to study hummingbirds and the plants they feed from at a forest reserve named Mount Totumas and in the adjacent Parque Internacional La Amistad. These sites are located in Western Panama on the border of Costa Rica, in a volcanic mountain range called the Talamanca Mountains. This region of Panama hosts immense biodiversity of both hummingbirds and plants, and is poorly studied. During this time in November, I found a deep passion for tropical ecology and learned a lot about hummingbirds at Mount Totumas. After talking with my advisor, Dr. Chelina Batista Mojica, we decided that a single sampling effort was not sufficient to try to publish these results, as tropical ecosystems are alive and active year round. Additionally, my data from a single sampling effort would not reveal the nuanced differences between the wet and dry season resulting from hummingbird migration and plant flowering patterns. This Venture Grant served as a follow-up to this original project, allowing me to collect data in March of 2023 during the dry season.

Hummingbirds (Trochilidae) are a large bird family of 362 species distributed across North and South America (Gill et al., 2022). Hummingbirds are easily recognizable by their small sizes, bright coloration, hovering flight, and nectivorous foraging on flowers. Hummingbirds and flowering plants have evolved mutualistic interactions in which hummingbirds pollinate flowers while feeding (Rodríguez-Flores et al., 2019). Avian pollination is most common in tropical regions, and is especially crucial for plants in cool, wet, montane forests (Dalsgaard et al., 2009). These montane cloud forests also host the world’s highest diversity of hummingbirds (McGuire et al., 2007), and are threatened by climate change and habitat destruction (Hofstede & Ojeda, 2013). Consequently, understanding patterns in hummingbird diversity and feeding interactions in tropical montane forests is essential. To gain a thorough understanding of these dynamics, observations during different seasons is essential. Seasonal differences may arise from monthly patterns in flowering (Sheldon & Nadkarni, 2015) and hummingbird migration (López-Segoviano et al., 2018).

• Repeated sampling in November 2022 and March 2023
• In both months, I sampled plots in three habitats:
  • Cloud Forest: 1800-2000 meters, 10 plots
  • Oak Forest: 2100-2300 meters, 10 plots
  • Garden: 1900 meters, 5 plots
• Three days of sampling in each habitat per month
  • 40 hours of observation total per month

• Repeated point-counts (timed observations) in plots
  • Counted and IDed hummingbird species within 25m radius for 20 minutes in each plot
  • Surveyed each plot 4 times (3 mornings and 1 afternoon)
  • Also noted the number of hummingbird visits to flowering plant species

• Compared sites with Kruskal-Wallis tests
• Compared seasons with Mann Whitney U tests
• Created hummingbird-plant visitor networks to visualize and describe plant-bird interactions using the bipartite package in R Studio

• 15 Hummingbird species observed in both seasons
  • 14 in November, 14 in March

Hummingbird abundance, richness, and visitation rates were significantly higher in the Garden than in the Cloud Forest or Oak Forest (p<0.05). The forest sites did not differ. This increased abundance is likely due to high floral density in the Garden compared to the forest sites.

Hummingbird abundance, richness, and visitation rate did not significantly differ between the November and March sampling effort across all three sites. However, there was significantly higher hummingbird abundance in the Cloud Forest and Oak Forest in the month of March compared to November.

Hummingbird-plant interactions differed between months. Network specialization, which highlights how many plants each species of hummingbird visits and how many hummingbirds visit each plant, was higher in November (rainy season) than in March (dry season).

• Clear differences between habitat types could relate to floral availability and habitat space
  • Forests have more dispersed floral resources and lower floral density
  • Garden has high floral density and thus can support more hummingbirds
• No clear significant differences in hummingbird abundance and richness between November (rainy season) and March (dry season)
  • Hummingbird presence at Mount Totumas seems to be stable over time
  • Community composition changed between seasons (which species were most abundant)
• Hummingbird-plant interactions were more specialized during the rainy season
  • Decreased floral resources in the dry season may have increased hummingbird generalization

• As plant species composition changes over small spatial scales in the tropics, increasing the scale of this study will provide more valuable results.
• Future study could investigate how hummingbird diversity and feeding interactions differs over a larger altitudinal gradient, from sea-level to high-elevation Paramo.
• Future study could also investigate how habitat destruction impacts hummingbirds and the plants they pollinate, especially hummingbird foraging specialization

This project represents a tangible step towards my goals of studying tropical ecology. Spending the Fall of 2022 in Panama changed my perspective on the world and ignited a fire of curiosity, and returning for this venture grant helped me pursue these questions and gain valuable field research experience. I hope to continue to analyze these data and write the results into a scientific paper. Publishing this paper will hopefully increase my experience and help me pursue similar questions in a PhD program starting in 2024! On a personal note, this venture grant also helped me pursue a new passion of wildlife photography, which I hope will allow my research to resonate with a larger audience. I also got to see many beautiful species other than hummingbirds, including the famous Resplendent Quetzal.

Thank you so much to the Keller Family Venture Grant and CC Department of Organismal Biology and Ecology for supporting the March sampling effort for this project. Additionally, I would like to thank Aly Dagang, Chelina Batista Mojica, and the School for International Training for supporting the November sampling effort. Finally, this work could not be possible without the kindness and hospitality of Jeff and Alma Dietrich at Mount Totumas, as well as everyone who works there.

Dalsgaard, B., González, A. M. M., Olesen, J. M., Ollerton, J., Timmermann, A., Andersen, L. H., & Tossas, A. G. (2009). Plant-Hummingbird Interactions in the West Indies: Floral Specialisation Gradients Associated with Environment and  Hummingbird Size.  Oecologia, 159(4), 757–766.  https://doi.org/10.1007/s00442-008-1255-z  

Gill, F., Donsker, D., Rasmussen, P., eds. (2022, August 11). Hummingbirds. IOC World Bird List. v 12.2.  https://www.worldbirdnames.org/new/bow/hummingbirds/  . 

Hofstede, R., & Ojeda, M.R. (2013). Report on the reactive monitoring mission to Talamanca Range La Amistad Reserves/La Amistad National Park – Costa Rica and Panamá from 17 to 24 January 2013. Report to the UNESCO World Heritage Committee, 37th  session, Phnom Penh, Cambodia, 16-27 June 2013, 1-20 p.

López-Segoviano, G., Arenas-Navarro, M., Vega, E., & Arizmendi, M.D.C. (2018). Hummingbird migration and flowering synchrony in the temperate forests of  northwestern Mexico. PeerJ, 6(6). E6131. https://doi.org/10.7717/peerj.5131

McGuire, J.A., Witt, C.C., Altshuler, D.L., & Remsen, J.V. (2007). Phylogenetic systematics and biogeography of hummingbirds: Bayesian and maximum likelihood analyses of partitioned data and selection of an appropriate partitioning strategy. Systematic  Biology, 56(5), 837-856.  https://doi.org/10.1080/10635150701656360 

Rodríguez-Flores, C.I., Ornelas, J.F., Wethington, S., & Arizmendi, M.D.C. (2019) Are hummingbirds generalists or specialists? Using network analysis to explore the mechanisms influencing their interaction with nectar resources. PLoS ONE, 14(2).   https://doi.org/10.1371/journal.pone.0211855  

Sheldon, K. S., & Nadkarni, N. M. (2015). Reproductive phenology of epiphytes in Monteverde, Costa Rica. Revista De Biología Tropical, 63(4), 1119–1126.  https://doi.org/10.15517/rbt.v63i4.1658