Butterflies and birds
Their routes are less impeded by topographical features like hills and valleys, and traveling through human cities and over human roads carries less risk if they can pass from a safe height well above people and vehicles. Despite these advantages, migration still remains a perilous journey for most.
Recently, scientists determined that millions of birds in North America are shifting their spring migrations earlier, at an average rate of 2 days per year. But as researchers note, bird migrations are influenced by a complex combination of factors, and there's concern that the migratory patterns of birds and the seasonal cycles of the plants and insects they depend on may respond differently to rapid environmental changes and fall out of sync, a phenomenon scientists call "phenological mismatch."
Monarch butterflies make one of the most incredible migratory journeys on earth. The tiny but iconic orange and black butterflies, each weighing about as much as a paperclip, travel up to 3,000 miles each way.
In the spring, multiple successive generations make their way north over a period of about 5 months. In the fall a single, long-lived "super generation" is born and makes the entire return trip to southern overwintering sites in one generation.
Their arrival in each landscape along the way must be perfectly timed to the blooming of nectar plants they rely on to refuel. Researchers worry that if monarchs' migration instinct is primarily driven by temperature cues, and flowers bloom primarily in response to light cues, climate change (which has not been accompanied by changes in light) could result in monarchs reaching an area too early or too late to find food.
Monarch migration appears to provide the butterflies with some level of protection against the parasite Ophryocystis elektroscirrha (OE). Because infected individuals are left behind during migration, their ability to infect subsequent generations of butterflies is reduced. In recent years, scientists who study monarch butterflies have recorded an increase in once-rare sedentary, non-migratory populations that have significantly higher rates of OE infection.
Become a citizen scientist!Report sightings of monarch butterflies and other wildlife to help scientists gather crucial conservation data.
The ruby-throated hummingbird's migration follows a route that closely mirrors that of eastern population of monarch butterflies, delighting bird lovers from Mexico and Central America all the way to the U.S. and Canada as they stop to sip critically important, high-calorie nectar or sugar solutions from backyard nectar plants and feeders.
But while the first eastern monarchs don't typically reach the United States until late March or early April, starting out for home in October, ruby-throated hummingbirds follow a different schedule, with reported first sightings in the U.S. as early as January and staying only until August or September before returning south.
One of the most prominent effects of climate change that we see today is the increase in extreme weather events. Warmer oceans produce more frequent and more intense storm systems, and the autumn hurricane season is a particularly dangerous time to be flying over water and coastal areas.
In 2005, Category 5 Hurricane Wilma blew thousands of migratory birds off course, flinging them even further from their southern destinations into northeastern Canada and even western Europe! The following summer, bird counts in Quebec revealed that the chimney swift population had been decimated by 50%.
In nature, healthy animal populations can often withstand an occasional devastating event like this, if given enough time to recover before disaster strikes again. The increasing frequency of destructive superstorms increases the risk of multiple severe storms wiping out populations faster than they can recover.
Destructive storms also put migrating birds at risk indirectly, when winds devastate key stopover habitat that birds use to rest and refuel on their journey.
In 1989 another Category 5 storm, Hurricane Hugo, obliterated three-fourths of the trees in Francis Marion National Forest near the South Carolina coast, devastating not only resident birds like the endangered red-cockaded woodpecker (whose eventual rebound from the tragedy is, happily, a conservation success story), but also depriving tropic-bound migratory birds of critical seeds, berries, and insects to fuel long journeys over open water.
And in 2008, the eye of Category 4 Hurricane Ike made landfall less than 150 miles from the winter habitat of the world's only natural flock of whooping cranes, narrowly avoiding tragedy for an endangered population of migratory birds that had only just begun to come back from the brink of extinction as a result of decades of painstaking conservation efforts.