Have you ever stepped outside and found a swarm of hummingbirds that seems to have materialized with the flowers? Or seen a bright orange oriole and thought that wasn’t here yesterday? Birds signal spring—or rather, they’re better than us at timing its arrival. Rather than checking the TV groundhog’s shadow, these birds estimate the arrival of spring from hundreds, sometimes thousands, of miles away.
Who are these birds? Neotropical migrants. Birds who spend the winter in the American tropics (think Mexico, Central America, South America), keeping warm and building up fat for the trip back. And then, in the summer, migrate to higher latitudes (the US and Canada) to breed. And if you’ve noticed that in the spring there are just more types of birds, you would be right. Neotropical migrants give us a taste of an ecological latitudinal gradient where the closer you get to the equator, the higher species richness (the number of species) there is.
These migrants defy our human-imposed borders and the more objective measure of geographical distance. They migrate incredible distances to travel north in the summer and south in the winter. Sometimes, these migrations happen overnight. The ruby-throated hummingbird makes a nonstop flight of 600 miles twice each year. For a bird that weighs less than a nickel that’s quite a feat! But it’s not just hummingbirds that migrate, there are 386 of these birds according to the Neotropical Migratory Bird Conservation Act. These include orioles, sandpipers, herons, flycatchers, swallows, and almost all warblers.
These feathered migrants demonstrate the interconnectedness of nature. Many of the birds we see in our backyard also call Haiti, Mexico, Honduras, the Cayman Islands, etc. home. Thus, though they might seem unrelated, the events and laws of all these other countries affect the US as well. For example, dichlorodiphenyltrichloroethane (DDT) was banned in the US in 1972 due to its negative effect on animal health and development (e.g., egg-thinning in bird species such as the bald eagle, which are then unable to reproduce) and some potential harm to human health.
However, in Mexico, the decisions to fully regulate DDT didn’t happen until 1996 (this was largely due to DDT’s role in controlling malaria, a disease whose transmission rate was higher in Mexico than in the US and Canada). Eventually, these laws resulted in a global treaty, the Stockholm Convention, to protect worldwide human health and the global environment from persistent organic pollutants, including DDT. It is worldwide policies like these that are most effective in protecting these migrants who have no concept of human politics.
In addition to protecting species from pollutants, we must protect habitats in all areas where migrants live. It’s not enough to protect a species’ breeding range in North America if they won’t have anywhere to stay in the winter. In the winter, the birds build up stores of fat to sustain the long migration back up north to breed. If they struggle to find food in their winter habitat due to deforestation, then less of them will be able to survive the difficult migration. The third type of habitat that needs to be protected is stopover habitats. They are, essentially, rest stops along migration routes, areas where birds rest and refuel before continuing their journey.
One of the most relevant neotropical conservation issues to the American consumer is coffee. Not all coffee beans are grown the same. And this has significant impacts on birds. Traditionally, all coffee was shade-grown. Trees provided shade for the coffee beans, the fallen leaves served as mulch, and the birds living in the trees provided natural insect control.
Nowadays, for the sake of maximizing space and therefore profit, shade-grown coffee has been replaced with plantations of “sun” coffee. Growing coffee in this way requires the use of fertilizers and pesticides and significant deforestation. This coffee is grown in monocultures in the tropics, removing ideal living spaces for neotropical migrants to spend the winter. (Here’s a link on shade-grown coffee if you’re interested in switching.)
Through their impressive aerodynamic feats, neotropical migrant birds remind us that we live on a planet that’s interconnected – a world where the tides affect the climate of deserts and where volcanic eruptions can change atmospheric circulation patterns. We are a planet where our choices affect the conservation of a rainforest 5,000 miles away. Most of us are stationary beings living in one city, so it’s hard to conceptualize the world as such an interconnected web. But neotropical migrant birds can be that bridge, that reminder for us. Next time you look out at the snow and notice all the hummingbirds have gone, remember, they haven’t disappeared. They’re off in their winter homes, already preparing to fly back to your backyard.
