Birds Of A Feather Vanish Together
The passenger pigeon used to be one of the most common bird species in North America with an estimated population of 3-5 billion in the early 19th century. Yet in 1914, Martha, the last known living passenger pigeon on the planet, died of old age. Martha has since become a symbol of the threat of extinction of bird species all over the world.
Even though species extinction has been happening for millions of years, the rate at which it is happening today is unprecedented. However, extinction is only the last stage in a process that we tend to ignore: loss of species abundance, or the number of individuals that belong to a species. Large declines in those numbers are harmful because they interfere with ecosystem services, many of which we mistakenly take for granted. Without a healthy ecosystem, drinkable water, the production of food, and climate stability are all at risk.
This study, which charted 529 species in the U.S. and Canada, found that there has been a net loss of 2.9 billion birds (or avifauna) since 1970. That is about 29% fewer birds than five decades ago, across a wide range of species and habitats.
The researchers used two independent methods to estimate the number of birds throughout the years studied. Firstly, they consulted multiple standardized bird-watching records to estimate the change in avifauna size. Birds are relatively easy to identify and count, and as a result, reliable records have been collected, some of which go back fifty years. Secondly, they consulted a weather radar (NEXRAD) which recorded the presence of nocturnal migrating birds at 143 stations throughout the U.S. between 2007 and 2017.
The bird-monitoring records showed that 57% (303 out of 529) of the surveyed species exhibited declines, and it was not only rare species who were affected. Common species such as sparrows, blackbirds, and swallows also suffered large losses. All in all, only 12 bird families, out of 67 surveyed accounted for 90% of the total loss.
Out of the ten breeding biomes that the study looked at (such as coasts, arctic tundra, and boreal forest), grassland had the steepest declines in bird population sizes. Of all grassland species 74% of them have been in decline, losing a total of 700 million individuals. Only wetland birds have gained a stronger presence with a 13% increase in population size. Waterfowl, such as ducks and geese, have increased in number by 56% in the last fifty years.
The weather-radar showed a steep decline in the movement of migratory birds, a reduction of about 14% in the last 10 years. This number conforms to the bird-watching data, strengthening the estimates of the study.
Human activities such as habitat destruction, intensive agricultural activity, and widespread use of pesticides are considered predominant drivers for this change.
Looking at the results overall, first we must acknowledge the bad news: bird-watching records suggest that if we do not act fast the declines will likely continue. This change is happening quickly, and not only in North America. Numbers of bird populations are also declining in Europe. Moreover, birds are one of the animal groups which we can monitor easily, but these losses potentially indicate declines in animal groups that we cannot measure as confidently.
And now the good news: firstly, as we so often remind our readers, data is important and powerful. We can, and must keep monitoring these changes in population sizes as they will alert us before it’s too late. Secondly, history shows us that conservation initiatives and legislation can work. Species that were endangered can recover, and we have prevented extinctions in the past. One example of effective legislation is the Migratory Bird Treaty Act which protects over 800 species.
As animal advocates, we need to pay attention to the loss of species abundance and take it as seriously, if not more, than species extinction. This study also underlines the need for vigilant data collection and analysis to help identify areas of concern, so that action can be taken as quickly as possible and potential disasters can be averted.