Songbirds Impacted by Elk?

Joint research conducted by the US Geological Survey and the University of Montana has shown a decline in trees and their songbirds in mountainous Arizona but also reduced songbird habitat quality due to prolonged plant eating by elk. Climate change has reduced snowfall in these mountain habitats, which allows elk to consume new tree shoots there when they normally wouldn’t be present, thus reducing songbird habitat.

What follows is an interview with one of the researchers, Thomas E. Martin, a University of Montana senior scientist and professor.

How much longer are elk staying in high elevations than they normally do?

It varies from year to year depending on snow, but in many recent years they stay all winter.

How do you track elk as they move around at various elevations, and seasonally?

This is work done by other biologists with Arizona Game and Fish dept historically using radio-collars.

How much of the plants at higher elevations are elk consuming, and why is it a problem?

Elk are consuming 90-95 percent of all new ramets (recruits) of some species like aspen and maple.

Have songbirds in Arizona mountains been declining for 22 years straight because of climate change reducing the snowpack there, which protects mountain plants from being eaten by elk?

Nothing in ecology is ever “straight.”  They have had a general decline with variation within this broader trend across the 22 years.  The decline in birds is caused by the decline in plant abundance – the fencing, which allowed plants to recover, verified that when the plants become available, the birds recover as well.

Does the declining snowpack in the mountains mean a significant loss of water when it melts for plants at elevation?

It can for some plant species because melting snow provides deep soil water that is not provided by rain, which is largely a runoff event.  Some plants rely on this deep soil water based on work by plant physiologists.

What can be done to preserve the plant life there and the songbirds?

Continued reductions in elk herd size and periodic fencing.

What impact does the loss of songbirds have on the local ecology – does it increase insect populations, and decrease the other  animals that eat birds, and their eggs?

One of the important results of the study is to show that ecosystems represent complex interactions among many members.  Birds provide food for other animals.  For example, red squirrels are one of the major predators on bird eggs and nestlings.  Red squirrels often are calcium and protein limited in their reproduction and contents of bird nests provide an important source.  As you say, birds have an impact on insect populations (several studies have shown this).  In short, birds are an important part of the ecosystem and loss of any such important parts affect other parts of the ecosystem.

How would you explain the concept of the ecological cascade effect to a lay audience?

Ecosystems represent a wide range of organisms that depend on each other. Affecting one component can affect more than one other component because of this inter-dependency.  For example, by affecting elk populations or presence, plants are affected because of browsing.  The cascade then occurs because plants alone are not affected, but instead the change in plants,  in turn, affect birds, mammals, and insects that depend on those plants.

Could re-introducing wolves, help reduce the elk population so the mountain plants can be rejuvenated?

The influence of wolves remains an open question.  Work in Yellowstone in recent years has begun questioning the importance of wolves on elk browsing impacts there.  Instead, work there too is finding that snow is actually driving elk browsing pressure (see the paper that is in press and online Brodie, J., Post, E., Watson, F. & Berger, J.  Climate change intensification of herbivore impacts on tree recruitment. Proc.Roy. Soc. Lond. B or the paper by Kauffman et al. in Ecology)

Image Credit: MONGO/Public Domain

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