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.
Looking Ahead: Soaring shearwaters use the international Important Bird Area of Stellwagen Bank National Marine Sanctuary as their feeding ground, traveling nearly 20,000 miles annually to do so. Another 52 seabird species are also supported by sanctuary waters. In exchange, these creatures support the ecosystem of the sanctuary as a whole and serve as vital indicators of environmental change.
These seabirds migrate up the eastern Atlantic coast in April in order to feed in the Gulf of Maine. They migrate in a “figure 8” pattern when they depart in the late summer or fall, traveling east across the Atlantic, south to the coast of North Africa, west across the equator to the Patagonia Shelf of South America, and then on to the South Atlantic’s Nightingale Island, Inaccessible Island, Tristan da Cunha, and Gough Island, where mature animals breed. The sand lance, which is the preferred food of these birds, grows in the sandy area beneath the waters of Stellwagen Bank. However, due to changes in prevailing wind patterns brought about by climate change, these birds may not be able to reach the productive waters of the sanctuary and other regions of the North Atlantic. Furthermore, these forage fish may become less productive and abundant in increasingly acidic waters, which would force great shearwaters to change their migration patterns in accordance with the areas where prey is still present in greater quantities.
The birds are excellent indicators of the health of the ecosystem and can even identify changes that may result from climate change because they are easier to see than species like sand lance, according to Wiley. We are able to monitor these changes in real time and gain additional insight into the abundance of prey species that sustain the ecosystem of the rest of the Stellwagen Bank National Marine Sanctuary by charting the annual migration of the predatory shearwaters, as Stellwagen Bank has done.
Scientists at Stellwagen Bank National Marine Sanctuary conducted their fourth cruise this summer since 2013 to record this well-known sand lance predator as part of an ongoing investigation into the birds’ flight patterns, feeding and foraging behaviors. Ten great shearwaters are tracked each year by scientists on board the sanctuary research vessel Auk using satellite tags. The tracking is done both inside and outside the sanctuary. This summer, in addition to the satellite tagging, great shearwaters had their breath, feathers, and blood sampled to find out what they had eaten in the previous days, weeks, and months, respectively. Additionally, the group collected samples from one manx shearwater and two sooty shearwaters, which were not previously part of the project.
Among the numerous seabird species that can be found in Stellwagen Bank National Marine Sanctuary are great shearwaters. They hunt for fish by diving underwater from the air or by snatching objects while swimming on the surface. In the sanctuary and other areas of the North Atlantic, the sand lance, also known as “sand eels,” is a major food source for the birds. These fish’s populations are dependent on oceanographic factors like water temperature, current flow, and nutrient availability; however, as the marine environment changes, these factors will probably change as well. For example, as the ocean surface warms, changes in upwelling currents may result in less nutrients being brought to the surface from deeper ocean waters, which would limit the amount of primary productivity of phytoplankton. Less primary productivity means less prey for sand lance, which translates to fewer sand lance available for shearwaters to feed on.
Throughout my more than 40 years in Chico, California, my hometown, I have witnessed changes in the bird population. There are a lot more of the recently arrived Eurasian Collared Dove and Northern Mockingbirds—I wrote about them in my previous blog post—but far fewer of the other species. In the wetlands outside of Chico, I used to see Yellow-headed Blackbirds, but they are no longer there. Owls that burrow were prevalent; almost every tire pile had one. Lewis’ Woodpecker, Yellow-breasted Chat, and Blue-gray Gnatcatcher are birds I haven’t seen in a long time. The main cause of this is California’s rapid growth, which is destroying habitat and packing more people into the habitat that is left. To say nothing of climate change, windows, and cats. And it is happening all over the world.
Because we have such a thorough understanding of their biology and life histories, birds make excellent indicators. Birds are present in nearly every habitat on Earth and almost everywhere in the world. They have a wide range of niche needs and consume a variety of foods. Because birds are mainly diurnal (active during the day), easily observable, and more easily studied than nearly any other large animal, we have a wealth of information about them. We thus have long-term data regarding their population sizes and ranges.
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.
For instance, the House Sparrow, a European native that was once widespread in Britain Its numbers have decreased by 268 percent, and as a result, it is currently regarded as a species of concern. It’s complicated, but basically, pesticide use, the introduction of non-native shrubs, and the paving of front yards for parking spaces are the reasons why House Sparrows are disappearing from cities and farms. This is also the case in India, where extensive fertilizer use is having negative effects.
Let’s continue to observe the birds closely as we go into the new decade, as they are attempting to communicate with us.
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