Why some bird flocks are fleeing the Phoenix area

Don’t be surprised if you start seeing fewer feathered friends in Phoenix.

Both local and migratory birds are spending less time in the Valley due to climate change and urbanization, according to a new study conducted by Arizona State University researchers.

They’ve discovered these flocks are fleeing the desert-city ecosystem for places with more friendly temperatures and less asphalt and concrete.

But they’re not fleeing forever. Researchers have also found that some bird species respond positively to changing landscape conditions and suggest that future land management practices may incorporate the benefits that city-dwelling wildlife provide to people.

It’s all spelled out in a recent article published by the Ecological Society of America in the journal Ecological Applications.

Jeffrey D. Haight, a member of Central Arizona-Phoenix Long-Term Ecological Research and a postdoctoral researcher with ASU’s Global Institute of Sustainability and Innovation, co-authored the new study with four other scholarsThey include Kelli L. Larson, ASU School of Geographical Sciences and Urban Planning; Fabio S. de Albuquerque, ASU College of Integrative Sciences and Arts; Heather L. Bateman, ASU College of Integrative Sciences and Arts; and Amy E. Frazier, Department of Geography, University of California, Santa Barbara.. He recently spoke to ASU News about the study, how birds are reacting to heat and urbanization, and what it means for the Valley’s ecosystem.

Note: Answers have been edited for length and/or clarity.

Question: What was the impetus of the project?

Answer: Our overall intent for this project was to contribute to much broader efforts to improve our understanding of the diverse ways in which people relate to their environment — to nature — within cities and how those relationships can evolve as the environment changes, with the ultimate goal of envisioning and building more sustainable futures for cities as they continue to grow in a changing climate. 

Our first goal was to look back and get a better picture of how the environment of metro Phoenix has changed over the last few decades. So we took advantage of some recent advancements in satellite imagery to build a series of snapshots of how rapidly the city has expanded out into the Sonoran Desert and the Valley’s farmlands, and how the city has generally gotten hotter and drier. 

Then, considering that new information, we set out to look at how combinations of those environmental conditions make the city habitable for different types of wildlife, leveraging decades' worth of records that CAP has collected about the diversity of birds that live among us here in the Valley. 

In particular, we were most interested in what’s going on with the birds that are known to have significant relationships with people and with the overall health of the ecosystem, which is why we take a closer look at certain groups of birds, such as those that can pollinate flowers, those that can disperse native plants, and those that can eat some of the insects that we consider pests.

Q: What was your most interesting or surprising finding in your research?

A: Well, one of the more important — but least surprising — things that we found is that the bird community has generally not responded well to the growth of the city. In areas that are more built, more urbanized, fewer species tend to stick around, and usually in smaller numbers. At the same time as the region has been urbanizing, the diversity and abundance of birds has declined. 

However, perhaps more interesting is that we saw that those negative impacts of urbanization were often not independent from the effects of other environmental conditions, such as climate and vegetation. When and where the weather is cooler, and the grasses and other plants are greener, you can find more birds in the city; but as it gets hotter and drier, species seem to spend less time in the city and are more likely to be seen out in the more natural desert habitats.

But where I think it really gets the most interesting is when findings diverge from those general patterns. While many bird species and groups of birds really strongly avoid the city altogether, some are relatively adapted to urban areas, and others have mixed responses. 

Some birds like places with more vegetation, while others like the drier areas with more natural desert vegetation. Some seem to handle the heat well, while others seem to be driven out of the city by it. Birds are different in what habitats they like and what kinds of stresses they can handle. 

Q: Your study essentially states that not all birds are the same — some can take the heat and some cannot. Can you tell us some of the factors in why some flocks stay and why others leave sooner because of climate change?

A: We can certainly make some educated guesses, especially when it comes to heat. For one, like us humans, birds have physiological limits to how much heat they can tolerate, especially when dealing with some of the other stresses of living in an urban environment. We and many other researchers have found there are indeed certain characteristics of different bird species, and even different individuals, that are associated with their responses to their environment, including the ability to “take the heat.” 

To use an example from another ongoing study of ours, we have found that the birds that seem to avoid urban areas when it’s hotter are larger-bodied species, especially waterbirds like the great blue heron, and native desert species like the cactus wren. The birds that were more common when it was hotter in our study seem to be those that already spend time in the city, perhaps because those species can more effectively take advantage of shade and irrigation, and other resources that the city has to offer.

As the climate warms, one might expect that the birds that are less heat-adapted, for one reason or another, might be the first to leave, while the species that are relatively tolerant of the heat might even become more common. That said, we are at a bit of an extreme end here in Phoenix when it comes to heat, so it is not hard to imagine that we could reach the limit of what even the most heat-tolerant species are accustomed to.

Q: What makes for a good habitat for these different types of birds?

A: Each species has its own habitat needs, but there are certainly some general patterns we can consider. Some species are specialists to a particular habitat — such as desert uplands or riparian forest — that provides them with the specific resources that they need to thrive. Several of the birds that are in greatest need of conservation are habitat specialists, in part because once that specific habitat is lost, it might not be so easy — or even possible — to restore it. 

Other birds are more of generalists, they can be found in a wider variety of habitat types, but they still generally need spaces that provide them with those key resources: food, water and shelter. 

Q: What can decision-makers/policymakers do to make the Valley more hospitable for wildlife?

A: For one, I think decision-makers can start by looking more toward the cases where policies and management actions have mutual benefits for people and wildlife. Extreme heat, for instance, is clearly a huge challenge for those of us living here in metro Phoenix, one faced by both us humans and by the critters. If it is the case that actions to mitigate the harm that heat causes to human health and safety also benefit the wildlife that people most appreciate and value, then I think it is worth knowing and acknowledging those broader impacts.

I think it’s also key to recognize that making places more hospitable for wildlife isn’t just about making sure species have all their habitat needs met. It’s also about ensuring that the people living in and near these spaces where the wildlife are spending time are willing to tolerate, accept or even encourage that wildlife being there. For anyone making decisions on how to create or maintain wildlife habitat, we may find it vital to confront how those decisions may lead to interactions between people and wildlife that can lead to both benefits and risks. 

Q: Is there more research to be done in this area? What are the next steps?

A: There is always more work to be done. With urban ecology research like this, the next important step is often to bring it back to the people, to work more directly with communities, to build better understandings of how different people interact with changing wildlife communities and how those interactions can both benefit and hurt the well-being of both the people and the wildlife. 

What do people think about the wildlife in their neighborhoods? Which types of wildlife do they like and support conserving and which do they dislike and regard as nuisances? Exciting work on these types of questions has been done through CAP LTER and its long-term research efforts — including the Phoenix Area Social Survey, led by my co-author and faculty co-mentor Kelli Larson.

I am looking forward to seeing where research on these topics is going next. These days, there is a lot of great new research being done around the world that examines the more human dimensions of wildlife in cities, and we will need a lot more of it if we are to build sustainable cities in which people and wildlife coexist.