Nav: Home

Too many Bambi are bad for the forest

January 30, 2017

Overabundant deer can spell trouble for people, including frequent car collisions and the spread of zoonotic diseases. But deer can also disrupt wildlife communities -- such as forest songbirds -- by eating away their habitat. In a new study published in Landscape and Urban Planning, researchers show that areas in the eastern U.S. with high deer numbers tend to have fewer birds that need forest shrubs. These species use low-lying foliage to hide their nests from predators and to hunt for insect prey. Unfortunately, these plants are also on the menu of the white-tailed deer.

And there are a lot of deer. In the past, deer numbers were relatively low, held in check by native predators such as black bears, mountain lions, and red wolves. Now, bears are largely restricted to the Appalachians, mountain lion range has retreated far west, and the red wolf is at the brink of extinction. Deer have fared much better under heavy human settlement in the east -- aside from predator removal, roads and housing slice the forest into pieces, providing forage at sunlit edges and cover in the woods. Virginia, where the study was conducted, may contain as many as one million deer. That's a 36-fold increase in the last 80 years.

While hunters partly filled the role of the departed predators, urban areas are largely off limits to deer harvest. Folks with high-power rifles will usually not prowl the local city park, and so deer mow down nearby gardens relatively undisturbed.

But overabundant deer don't stop at daffodils. As more deer pack suburban forest fragments, they denude understory greenery and with it songbird habitat. The authors found that study sites with many deer were virtually devoid of species like the Hooded Warbler, White-eyed Vireo, and the Prairie Warbler -- species that rely on the forest undergrowth. Most of these birds are already in trouble due to habitat loss. The Prairie Warbler, for instance, a perky yellow bird with streaked sides, has been designated a species of conservation concern following range-wide population declines.

Counting deer and woodland birds was tricky. Adequate assessment of bird numbers required knowledge of their vocalizations, repeated visits to study areas early in the morning when birds were most active, and lots of statistical modeling. Deer are skittish and active at night, but they do leave tangible evidence of their presence - poop (this evidence is especially copious after a bellyful of warbler habitat). As though counting droppings wasn't fun enough, estimating deer numbers also required lots of statistical work.

Researchers estimated bird and deer numbers at two regions of Virginia - one on the coast and one inland. Coastal Virginia is more urbanized than the rural inland, and correspondingly the study found more than twice as much forest fragmentation there. The coastal region - with as many as twenty-eight thousand droppings per hectare - is where the study found significant correlations between deer and birds. "There were a lot of deer" says Vitek Jirinec, a coauthor of the study. "One of our vehicles was hit by a deer while going out for surveys - it ran into the side of the car and dented the door. Maybe the deer were onto us."

The fact that humans affect wildlife populations is not new, but sometimes the story is more complicated. This study suggests our land use practices that promote high deer numbers might be changing local ecosystems - with implications for declining songbirds and the people who enjoy them.
-end-
Article reference:

Vitek Jirinec, Daniel A. Cristol, and Matthias Leu. "Songbird community varies with deer use in a fragmented landscape." Landscape and Urban Planning 161 (May 2017): 1-9. http://dx.doi.org/10.1016/j.landurbplan.2017.01.003

American Ornithological Society Publications Office

Related Predators Articles:

Marine predators: Bigger in size with an appetite to match
The size of marine invertebrate predators has increased over the past 500 million years, while the size of their prey has not, a new study reveals.
Predators are real lowlifes
By deploying green clay caterpillar models across six continents, researchers unmasked an important global pattern.
Fish step up to lead when predators are near
Researchers from the University of Bristol have discovered that some fish within a shoal take on the responsibilities of leader when they are under threat from predators.
Restoring predators and prey together speeds recovery
Restoring predator and prey species together helps accelerate ecosystem recovery efforts compared to pursuing restoration of one species at a time, new research concludes.
Recovering predators and prey
Researchers show how simultaneously restoring predators and prey is much faster and more effective than doing so one at a time.
Reducing pressure on predators, prey simultaneously is best for species' recovery
Reducing human pressure on exploited predators and prey at the same time is the best way to help their populations recover, a new study indicates.
When it comes to predators, size matters
When it comes to predators, scientists find larger sheephead that consume bigger urchins help keep that population under control.
Birds of a feather flock together to confuse potential predators
Scientists from the universities of Bristol and Groningen, in The Netherlands, have created a computer game style experiment which sheds new light on the reasons why starlings flock in massive swirling groups over wintering grounds.
For viral predators of bacteria, sensitivity can be contagious
Scientists have shown for the first time how bacteria with resistance to a viral predator can become susceptible to it after spending time in the company of other susceptible or 'sensitive' bacteria.
How miniature predators get their favorite soil bacteria
Tiny predators in the soil can literally sniff out their prey: soil bacteria, which communicate with each other using scent.

Related Predators Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...