Jamaican Hummingbird Study Reveals Secrets of Species Survival

Research conducted by ornithologist Gary Graves has uncovered critical insights into the survival of Jamaica’s two distinct species of hummingbirds, despite their ongoing hybridization. The study focuses on the red-billed and black-billed streamertail hummingbirds, which continue to maintain their unique identities even in close proximity along the Rio Grande River.

Over the past three decades, Graves has made numerous trips to Jamaica to investigate why these two species remain separate. The red-billed streamertail, known as Jamaica’s national bird, can be found across most of the island, while the black-billed streamertail is restricted to the eastern tip. Their coexistence along the narrow hybrid zone presents a unique opportunity to study speciation in real time.

Decades of Research Yield Insights

Graves’ journey began after a collaboration with Javier Piedra, a former financial advisor who facilitated a debt-swap agreement aimed at supporting environmental initiatives in Jamaica. This funding allowed Graves to begin his research, initially focusing on other bird species before delving into the streamertails.

After years of establishing relationships with Jamaican government and local ornithological communities, Graves and his team collected numerous hummingbird specimens from the Rio Grande Valley between 2003 and 2006. The collection included over 30 specimens gathered by Caroline Judy, a former research associate at the Smithsonian. These samples have become integral to understanding the physical and genetic characteristics of the hummingbirds.

Through baseline analysis, the team discovered notable differences in bill morphology between the two species. The red-billed streamertails possess wider and thicker bills compared to their black-billed counterparts. Despite these differences, the key question remained: why do the two species not interbreed more frequently?

Female Preferences Keep Species Distinct

In a paper published in PNAS Nexus earlier this year, Graves and his colleagues revealed that female preference for bill coloration plays a significant role in maintaining the separation between the two species. Males, known for their promiscuity, will mate with any receptive female. However, females display a strong preference for males with either bold red or shiny black bills, traits that indicate maturity.

Juvenile red-billed streamertails exhibit mottled red and black bills, similar to those of adult hybrids, making them less appealing to potential mates. This selective mating behavior acts as a natural barrier, preventing the two species from merging into a single population despite their ability to interbreed.

Graves emphasizes that understanding this selective mating process is crucial for comprehending the evolutionary dynamics at play. He believes that the ultimate explanation for females’ avoidance of juvenile look-alikes lies within the genetics of the streamertails. The research team is currently analyzing the entire genetic code of the specimens, which comprises over 1.2 billion base pairs of DNA per bird, to identify the specific genes influencing female preferences.

As Graves approaches retirement from his role as a research zoologist and curator at the National Museum of Natural History, he reflects on the journey that began three decades ago. He plans to continue his involvement with streamertail research as an emeritus, ensuring that the project carries on under the guidance of younger scientists passionate about these unique birds.

Graves has expressed satisfaction in knowing his research will continue beyond his career. “I’m determined not to let this project end with me,” he stated. “I’ve already passed the torch to young, eager scientists who are just as passionate about these hummingbirds as I am.”

In a world where hybridization is increasingly common, the distinct behaviors of female Jamaican hummingbirds highlight the intricate balance of nature and the ongoing quest to understand biodiversity.