According to the American Bird Conservancy, birds are changing territories by the droves due to rising temperatures, expanding into new areas and even abandoning old ones.
Most of these changes appear to have a northern bias to them; as temperatures on average increase, birds are driven north seeking cooler summer climates. This influx means whole new mouths to feed in areas that never before had to feed them. As a result, there is more competition for existing resources, and something inevitably has to give. The ecosystems being left behind are also losing key parts of themselves when the birds depart, leaving niches unoccupied. In some cases, this can have catastrophic effects: endangered species that are dependent upon specialized habitats to survive could wind up decimated or even destroyed outright if climate changes rob them of their homes.
Migration itself is becoming a challenged notion. An increasing number of birds are deciding to forgo migrating altogether, usually because an increase in temperature renders the journey moot. Milder temperatures might mean more prey as well, allowing larger populations to stay put rather than fly south. While this may sound beneficial, even convenient for some birds, there are definitely downsides. If fewer birds are leaving, that means more animals competing for resources than there were before. Can numbers hold? Some birds still migrate but now stay later or return earlier, depending upon the situation. The American robin has been seen returning to their breeding grounds in the Rockies earlier and earlier each year as a result of rising temperatures. They are coming so early now, in fact, that they are arriving before the annual spike in the insect population that traditionally fuels their breeding period. The food they require to nourish themselves and their offspring isn’t available when they need it. In such ways, entire systems go into a tailspin.
A 2003 report by National Geographic documented an unexpected event for U.K. owls: they were breeding in the middle of winter, a time when they traditionally had to focus on survival. Rising temperatures delayed the arrival of normal winter conditions, and as a result, there had been a boom in the rodent population, allowing the owls to clutch well ahead of schedule. Without the changes in temperature, the rodents wouldn’t have flourished and the owls would have had to wait until later to lay their eggs. In this specific case, perhaps, climate change worked in their favor. But what about the robin going home to roost, only to get there before there are enough insects to feed her and her young? What about local species that suddenly have an influx of outside animals competing with them for an in-demand food supply that can only feed so many mouths? What about the rodents who find themselves under increasing pressure every winter by more and more hawks who have decided to stop migrating?
The world is constantly in flux, but as changes like these accelerate, more and more species, more and more environments, are pressured into adapting. In the short term, a family of owls may prosper, even if in the long term the entire ecosystem they belong to will have to rework itself from the ground up in order to support its changing demographics.
Robins may find themselves and their babies going hungry. The world may find itself a very different place.