The Garden Professors™

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. 

 

It’s ‘Wildlife week’ on the Garden Professors.  One of the most common questions that we get when speaking to garden groups is, “What can I do around my home to promote wildlife?”   My stock answer used to be, “Throw a party!”, but only a handful of people ever got it so I’ve backed off of that one.  Anyway, since the subject of gardening and wildlife comes up so often we’ve decided to dedicate a week to the topic.

Questions about wildlife (the animal kind) always take me back to my undergraduate forestry days at Washington State University and Dr. Zamora’s Wildlife Management course.  Even though I’ve always been more of a plant person than and an animal person, I found this to be a fascinating course.  In fact, assembling the winter browse twig ID collection was one of my proudest undergraduate achievements.  Doesn’t seem like much; but try wandering the Palouse hills in the dead of winter and see if you can indentify 50 browse species without the benefit of leaves, you’d be proud too!  In addtion to a notebook full of mounted twigs and a mild case of frostbite, I took away from the course several key principles of wildlife management that have stayed with me over the years.

What do wildlife need? In general, all wildlife need four basic elements: food, cover, water, and space.  The specific types and amounts of these elements, of course, will depend on the type of wildlife you wish at attract.  Homeowners can provide or enhance these elements through plants or through other, non-living means.   Important non-living components include feeders, bird-baths or other water features, piles of rocks or sticks (provide cover for small animals), salt, and standing or fallen dead trees (provide habitat for cavity-nesting birds and mammals).  Plants can provide both food and cover.  Important plant components in designing for wildlife include evergreen conifers for cover, summer fruits and berries, fall fruits and seeds, winter fruits and seeds, flowers that provide nectar, and trees that provide nuts and acorns.

At this point the questions often turn to the importance natives versus exotics.  In light of Doug Tallamy’s book, Bringing Nature Home, many people assume that only native plants can serve these functions.  But there are several factors to consider here.  First, Tallamy’s discussion is largely focused on co-evolutionary relationships between native plants and native insects, and even here some of the reasoning is stretched thin (see Linda’s Feb. 12 post).  There is more to supporting wildlife on a broad scale than insect/herbivore interactions.  Non-invasive exotic conifers, for example, can certainly contribute winter cover, vertical structure, and edge effects.  And, while some animals have evolved very specific diets (think koalas and eucalyptus), many herbivores are generalists and in some cases even prefer to feed on exotics.  So, in thinking about wildlife it’s important to consider function and providing the elements animals need than to simply fixate on whether plants are native or exotic.  This is especially true on tough, disturbed sites where natives may be poorly adapted and unable to survive.  Habitat provided by an exotic will be preferable to no habitat at all.

Lastly, another factor to consider is whether attracting wildlife around your home is always a good idea.  Along with the wildlife we’d like to see, improving habitat may increase the likelihood of running into critters (skunks, raccoons, possums) that we’d rather not encounter on the way to take the trash out late at night. Also, in many parts of the country, people and their pets are encountering large predators such as cougars and bears with increasing frequency.  Obviously a lot of this is due to human encroachment into the predators’ habitat, but it may be prudent to consider a ‘defensible space’ strategy as we do for wildfires. Keep the elements that are likely to attract larger animals a safe distance from the house.  Stay tuned for more as ‘Wildlife week continues’.

NOTE: Thanks to my high school choir-mate and college soccer team-mate, Tim Schlender for the timely wildlife habitat cartoon.