Like more songbirds? Eat more deer.
That somewhat startling directive comes from a study published in the British Journal of Applied Ecology, wherein University of Nottingham ecologist Markus Eichhorn explored why woodland birds were disappearing.
His team used lasers to build 3-D maps of English woods, and discovered that places with high deer populations had less than one-third the shrubbery under two meters tall that deer-free forests enjoyed.
“It is clear from our research that if we want to encourage more woodland birds, then we need to take action to restore the woodland structures they require,” Eichhorn said in a press release. “But in many areas it will need a drastic reduction in deer to have any real impact.
"We should not think of it in terms of a cull. We already eat venison in Britain but a large proportion of that is farmed meat. If wild-caught deer appeared on our menus or in the local butcher’s, it would encourage people to eat venison as readily as beef or lamb and would help conservation in our woodland areas.”
The United Kingdom has considerably more deer challenges than Western Montana. Eichhorn contends with roe deer and red deer, fallow deer, Reeves’ muntjac, Chinese water deer and sika deer. Those herbivores in turn drive down populations of nightingale, marsh tit, willow tit and lesser spotted woodpeckers, among other avian species.
Deer eat the bushes and saplings birds need for cover, forage and nesting material. And when concentrated in urban areas, safe from natural predators, they can become an ecological pest. That’s a problem any Missoula gardener knows too well.
“Deer are killing more of our plants than lack of water,” Missoula City Conservation Lands Manager Morgan Valliant said. “They’re our No. 1 cause of mortality for planted material in our parks and open space.”
While he hadn’t heard of the songbird connection, Valliant said he was very familiar with ungulate impact on the city’s river corridor, Rattlesnake Creek and other neighborhoods on the edge of deer country. An exclosure fence set up around a five-acre plot next to the PEAS Farm in the upper Rattlesnake Valley showed remarkable results this spring.
“Just by excluding the deer, we got thigh-high and waist-high trees coming in after one year,” Valliant said. “This summer we’ll be installing some more grazing exclosures and wildlife cameras to monitor the impact of deer on forest recruitment. We’re trying to get a feel for the differences across the valley floor.”
Urban deer became such a problem in Helena, the city sought and got special permission to kill them within the city limits in 2003. That program continues, with a quota of up to 250 kills a year to keep the density down around 25 deer per square mile.
Missoulians can’t legally kill deer within the city limits, and Montanans generally can’t either outside the annual big-game hunting seasons. The notable exception is the state’s road-kill permit system, which allows the collection of deer, elk and moose accidentally killed by vehicles on roadways. While the program issued almost 1,300 permits in 2015, Montana Fish, Wildlife and Park spokesman Ron Aasheim said no statistics are available for how many were applied to carcasses found within urban areas.
One unexpected finding of the British study was what happened to the surviving trees in deer-munched urban forests. The 3-D images showed those trees tended to be an average 5 meters taller than places with low deer populations – something the researchers had no explanation for. But the grazing impact on young trees was clear.
“This strong effect of the deer population demonstrates that we are not going to solve the problem by forestry management alone, which we found to have relatively minor effects on woodland structures,” Eichhorn said. “We still need to do more work to determine what levels of deer density are required to restore complex forest understory habitats, and the best ways to maintain these in the long term.
“There is no such thing as natural woodland in the UK,” Eichhorn added. “They are managed and shaped by human activity and if we want more woodland birds in our forest then we need to take action to achieve that aim. Anything which has a benefit for one species is likely to come at the cost of another.”