Ecological indicators are useful tools for measuring changes over time, and provide valuable insights into how and why the environment is changing. We can measure the changing status of the environment, such as biodiversity – fewer species, more species, and/or different species; the reasons for these changes (habitat destruction or degradation, pollution, climate change, introduced species, etc.), and the response to those threats – conservation, revegetation, new laws or policies, and public knowledge. By monitoring ecological indicators over time, baselines can be established from which trends can be quantified and addressed.
Birds are excellent indicators because we know so much about their biology and life histories. Birds are found almost everywhere in the world and in almost every habitat. They eat a variety of foods and as a ground have a broad range of niche requirements. We have lots of information about birds because they are more easily studied than almost any other large animal and they are easy to observe and they are primarily diurnal (active during the day.) As a result, we have long term information about their population sizes and ranges.
An example is the House Sparrow, native to Europe, was once common in Britain. Its numbers have dropped there by 68% and it is now considered a species of concern. What could be happening? It’s complicated, but basically House Sparrows are city and farm dwellers and insects are disappearing from cities and farms due to pesticide use, the introduction of non-native shrubs, and the paving of front yards for parking spaces. The same is true in India where heavy use of fertilizers is also having an impact.
The Western Meadowlark, although still fairly abundant, has been declining due to habitat loss and pesticide use.
The American Dipper requires a habitat of clear, mountain streams, but has declined due to the siltation of streams caused by land development and forest fire runoff. The Gray Jay has become less common in southerly parts of its range, apparently because its food supply has been affected by rising temperatures due to global warming. Greater Scaup and other tundra-breeding birds are declining as the permafrost melts earlier and more temperate predators move north in response to global warming. Earlier I cited many examples of birds around the world changing their ranges due to global warming. You can read a detailed report on birds and climate change at the American Bird Conservancy.
In the over 40 years I have been in my home town of Chico, CA, I have seen bird populations change. There are more Northern Mockingbirds – I blogged about them earlier, and a lot of the new invader, the Eurasian Collared Dove, but a lot less of other species. I used to see Yellow-headed Blackbirds in the wetlands on the outskirts of Chico; no more. Burrowing owls were common, nearly every pile of tires sporting a burrow. I haven’t seen a Lewis’ Woodpecker, Yellow-breasted Chat or Blue-gray Gnatcatcher in many years. The growth of California is largely responsible as it destroys habitat and puts more people into the remaining habitat. To say nothing of climate change, windows, and cats. And it is happening all over the world.
As we enter the new decade, let’s keep a continually close eye on the birds because they are trying to tell us something.