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Nesting Instinct: When Birds Change (Genetically-Coded) Flight Plans

A Kirtland’s warbler. Source: U.S. Fish and Wildlife Service Midwest Region

From northern Illinois to southern Europe, birds are feeling the effects of climate change. People are seeing new guests at backyard bird feeders, or their absence as insect pests hit crops. Chris Whelan, an ecologist at the University of Illinois at Chicago and co-editor of Why Birds Matter, has tracked these changes closely. Below, Whelan shares his insights on how birds are adapting — and not — to a warming planet. This interview has been edited for length and clarity.


My colleagues and I are studying nesting, comparing the behavior of northeastern Illinois birds with their counterparts from the late 1800s. We’re matching historic Field Museum nests and their notes with more than 14,000 modern nests.

At the most extreme, one species is nesting an average of 30 days earlier than it did in the late 1800s. For others, the impact is much less pronounced. Some species have not shifted at all. Keep in mind there are more than 10,000 bird species. Some are responding to a changing climate. Some are not.

One worry with climate change is that the timing for bird breeding may not match the availability of edible insects and plants. Even if they eat seeds or fruit at other times, when breeding, many birds eat insects. Without them, they cannot raise their young.

Caterpillars are an indispensable source of food for birds. Source: Pexels

Consider caterpillars. In the fall, a female moth lays eggs that overwinter on the bark of a tree. The following spring, the tree leafs out and the eggs hatch, the caterpillars move out to the leaves, consume them, and then pupate to later emerge as adults. That is their life cycle. For some birds, reproduction is timed for when caterpillars are abundant.

By the time a bird claims a territory, attracts a mate, builds a nest, lays eggs, and the eggs hatch, there needs to be food to feed the young. With a mismatch, there may be too few insects and the young may die of starvation. That’s the big fear. Some bird species are already shifting nesting to the earlier dates — but others are not. So, over the long haul, there may be winners and losers.

In Europe, research is showing that, as temperatures warm, some bird species are changing migratory patterns. There’s evidence that the routes are pre-programmed genetically — they’re inherited — and there’s evidence that heritable navigation skills are evolving with climate change.

This is rather extraordinary. On the plus side, species can potentially evolve quickly — pretty much in real time. While that’s a positive finding, it’s by no means universal. Other traits may not evolve so quickly, and one concern is there won’t be enough food for some birds to reproduce. If they’re not reproducing, they can’t evolve.

Birds eat insects that damage apple trees. Source: Pexels

Also, in Europe, research is showing some avian predators are shifting north. If the ranges are shifting, pest control may shift north with them — insect pests in forests and vineyards, rodents that attack maize and grains. If the ranges of predators shift, northern Europe may benefit, and southern Europe may be hurt. Changes are not going to happen uniformly across the globe.

Some of the biggest impacts from range changes may come from how birds handle pests. Many of the insects that birds eat damage plants we rely on, whether for commodities, like lumber, or food products, like soy and corn. When birds are present, apple orchards are more productive. Birds consume the insects that damage trees — fewer leaves means fewer resources to produce apples. They also consume the insects that infest the apples. If you don’t want to bite into an apple and find half a worm in your mouth, you want birds around.

Another impact of climate change on birds will impact people directly: the pastime of birding will change. More people engage in bird-watching and feeding birds than in hunting or fishing. It’s a huge industry. People will be both delighted and disappointed as the ranges shift around. Some favorite backyard birds may not be favorite backyard birds 20 years from now. But for other locations, birds that had been few and far between may start to show up.

Blackberries depend on birds to disperse their seeds. Source: Pixabay

It’s also important to consider pollination in agriculture and horticulture, as well as in nature. In some parts of the world, the role of birds is huge. If that disappears, some plant species disappear. For example, consider black cherry trees. Their successful reproduction depends upon successful distribution by birds. The same is true for blackberries and raspberries. We cultivate them, but they also occur in nature. I grew up in southwest Wisconsin, and growing up out in the country, my friends and I knew every patch in two or three valleys. They are dependent on bird species for dispersal.

Finally, there’s the issue of scavenging. There are tremendous numbers of animals that die around the world, and if those carcasses aren’t consumed by something, you would be surprised how quickly they’d build up. Much of that scavenging is done by birds. In fact, the only obligate vertebrate scavengers are birds — vultures and condors. Many people think scavenging is gross. Many people think vultures are ugly, but they provide a huge, huge service.

A vulture, nature’s Miss Congeniality. Source: Pixabay

Scavengers’ impact became apparent a few years ago in south Asia when four species of large vulture went almost extinct. The cause was a veterinary chemical called diclofenac, an anti-inflammatory used in livestock. It remains in the tissue of an animal, say a cow, after it dies. Traditionally, farmers would take dead animals far out in a field and let the vultures take care of them. Diclofenac kills vultures quickly, so the region experienced a more than 90 percent vulture population decline in an alarmingly short number of years, and the carcasses just kept building up. That led to a profusion of feral dogs, rats and other vermin, and the net result was a greater transmission of disease. It led to tens of millions of dollars in medical expenses, with rabies and other conditions. Birds provide an absolutely critical regulating service for human disease.

In North America, research suggests turkey vultures and black vultures may actually benefit from climate change, along with northern mockingbirds, American robins, and northern cardinals. However, the species ecologists believe may fare poorly include trumpeter swans, three-toed woodpeckers, gray jays, Clark’s nutcracker, Kirtland’s warbler, Bicknell’s thrush, sage thrasher, greater sage grouse and Bell’s sparrow, among hundreds of others.

It depends on the scale at which you look at it. If you look globally, we’re seeing some species already impacted. The effects of climate change vary geographically.


Chris Whelan is an avian ecologist at the University of Illinois at Chicago and research associate at the Field Museum. This interview was conducted by Josh Chamot, who writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.