We’ve posted before about the native vs. nonnative conundrum, especially as it relates to invasive species. So let’s complicate the issue a bit more by considering how birds are affected by our landscape choices.
About 10 years ago my UW colleague Sarah Reichard and I collaborated on a literature review on the interaction between birds and non-native plants. While we know that invasive plants can displace native plants and create less biodiverse environments, the resulting impact on species like birds is not so cut and dried. And what about noninvasive, nonnative plant species? How do they affect bird populations? Here are some of the practical bits of information that we found:
1) Nonnative shrubs and trees are often chosen for their brightly colored fruits, especially those that produce them in a different season than native plants. Winter color is highly valued by gardeners.
2) Frugivorous birds (those that eat fruit) generally benefit from the introduction of fruiting species as an additional food source, even if the species is invasive.
3) Birds tend to prefer fruits that are red and/or black, or that have red arils or pseudoarils.
4) Birds tend to prefer fruits that offer the most pulp; interestingly, highly invasive plants species tend to have larger fruit displays and therefore higher bird usage than less invasive relatives.
5) Additional food sources can allow frugivorous and omnivorous birds to expand their ranges and/or their breeding seasons.
6) Nonnative shrubs and trees with structural features such as thorns and spikes can provide protection to small birds from predators.
It’s clear that birds are highly adaptive and will quickly learn to utilize new food resources – and in doing so, may contribute to their spread through seed dispersal. It’s enough to make your head spin.
Here’s what I recommend for choosing bird-friendly trees, shrubs and vines:
1) Use native species first if they are adaptable to your site conditions. (Note: many native species, especially those of forested environments, don’t like urban conditions.)
2) Be sure to provide structural diversity in your landscapes – groundcovers, small dense shrubs, larger open shrubs and small trees, big trees, and vines – to provide shelter and nesting habitat.
3) Before choosing nonnative species, check the web for information on invasiveness. The USDA Plants Database (http://plants.usda.gov/) has information on invasive species. If it’s invasive, please don’t plant it!
4) Birds see best in the red end of the color spectrum, so select plants with fruits and flowers that will attract them.