A female ruby-throated hummingbird (Archilochus colubris) plays with the strands of a spiderweb on an old stem. Many hummingbirds are known to incorporate silk into the outermost layer of their cupped nests, binding lichen and plant fibers together for camouflage. Females will alone construct the nest and provide care for the eggs and chicks.
Although hummingbirds are not the first birds to come to mind when thinking of latitudinal migrations, they can be adept long-distance fliers. Ruby-throated hummingbirds migrate to escape frigid temperatures, wintering in the southern U.S. and Central America before returning to their breeding grounds in the spring. Some individuals of this species travel 1500 kilometers without stopping. Assuming a flight speed of about 30 kilometers per hour, and underestimating their wingbeats per second to around 50, this would come out to an astonishing 9 million wing beats in a single flight! However, not all migrants follow this non-stop trajectory, acquiring food resources again in the Gulf Coast before continuing their journey. To deal with such high energetic costs during travel, hummingbirds prepare by gorging themselves to the point of doubling their fat deposits.
With urbanization and human encroachment on natural habitats, the vast majority of native species do not fare well. Some may prove themselves as adaptable or simply capable of weathering the new conditions, in some cases even thriving due to drastic declines of other species that compete for the same resources. But most are ill-equipped for the urban jungle. In the case of hummingbirds, one study from the cities of southeastern Brazil has shown that hummingbird species relying on specialized diets (e.g. feeding from the flowers of particular plant species) were unable to persist in urban environments. Co-occurring hummingbird species that instead have generalist diets benefit from artificial nectar stations in cities, and also exclude other species through aggressive interactions at feeding sites.
Apart from changes in hummingbird community structure, another extremely common cause of bird declines in cities is from collisions with windows. In fact, second to habitat loss, window collisions are estimated to be the greatest human source of avian mortality— with conservative estimates of up to one billion birds killed every year in the U.S.. Pictured above is one of the unlucky survivors, a juvenile ruby-throated hummingbird I found today panting with its eyes closed on the concrete. In its state of health, I thought it was a goner, but after some emergency gatorade (later sugar water) and two hours of recovery time, the hummingbird’s heart rate reduced dramatically and it finally opened its eyes. About three more hours and the hummingbird was only able to fly about five meters outside, so I’m keeping it overnight to regain more strength. There’s no telling how long the bird was stressed and overheated after hitting the window, but I’m hopeful at the possibility of its return to the wild.
I’m glad to have happened upon this tiny green iridescent speck on the ground, especially before ants had found it, but this hummingbird is just one of thousands and thousands to strike windows on that same building. If you remember my earlier posts of releasing a mourning dove and cardinal, it’s at that same spot. So what are some solutions? Much research is going into developing window coatings that are detectable by birds (particularly through reflectance in the UV or due to nanostructures) but invisible to humans. Alternatively, effective and easily implemented options are the use of physical barriers in front of windows or opaque objects placed on the window’s outer surface. For example, screens, stickers, and visible patterns can substantially reduce collision rates with smaller windows in your own home.