In the cloud forests of northern Peru, a surprising behavior has emerged among tropical birds. According to a recent study, these birds are modifying their breeding calendars in an unprecedented way.
During five years of research, it has been observed that insectivorous species can delay their breeding by up to half a year, even varying between nearby mountains.
The main factor seems to be precipitation. Changes in rainfall alter the availability of insects, which in turn affects the reproductive decisions of the birds.
When the climate becomes unpredictable, the fluctuating food supply complicates the feeding of the chicks.
The study was led by Felicity Newell and Ian Ausprey, professors at Texas A&M University, with the collaboration of Scott Robinson from the Florida Museum of Natural History.
The team worked on eight mountains of the Andes, covering more than 100 kilometers, to understand the nesting patterns of the tropical birds.
Effects of climate change
Their approach included capturing birds using mist nets to look for signs of recent breeding. They also measured flora, fruits, precipitation, and insect biomass, linking these data with the birds’ reproductive cycle.
The exhaustive fieldwork resulted in the capture of more than 8,000 birds and the recording of nearly 4,000 reproductive events.
About 48,000 insects were collected, and 318 nests were located, demonstrating the importance of persistence and hard work in field ecology.
It was previously believed that in the tropics, reproduction could shift only a few weeks. However, this study suggests that variations could be much greater in areas with well-defined wet and dry seasons.
Most significantly, it’s not just one species changing, but entire segments of the community.
Particularly notable was the finding that insectivorous birds experienced an unforeseen variation, with communities out of sync by up to six months in areas separated by just 60 miles.
One community could breed in May and another in October, a phenomenon not documented near the equator.
The team determined that the tipping point for breeding in one season or another is closely linked to insect biomass, with a threshold of 43 milligrams per square meter.
Above this, birds could breed at the end of the dry season, but below it, they did so at the start of the rains.
This behavior is influenced by climatic fluctuations, where periods of drought or heavy rains reduced arthropod biomass by up to 50%.
However, moderate conditions favored an increase in biomass, indicating a crucial ecological balance.
The environmental repercussions are evident. The study does not imply that all birds will change their reproductive patterns, but it suggests they might if food levels drop.
With increasingly extreme and irregular rainfall, insects, and therefore the birds that depend on them, could be the first to be affected.
Additionally, the pressure does not only come from the climate. The Andes are a biodiversity hotspot with more than 1,500 bird species. Deforestation for agriculture has been linked to a decrease of up to 60% in the number of species.
Hope lies in local actions. Studies suggest that increasing tree cover in agricultural systems can improve biodiversity, increasing species richness by 18% to 20% by introducing more vegetation per hectare.
