American Bird Conservancy News
Humans Stress Birds… & Marbled Murrelet Plea…New Study Says Stress from Human Activity Can Cause Urban Birds to Abandon Nests Ten Times More Often
(Washington, D.C., May 13, 2013) A new study from scientists at Boise State University shows that even bird species considered “tolerant” of human activity, such as American Kestrels, may be adversely impacted by human disturbance to a far greater degree than many had believed.
The study, authored by Erin H. Strasser and Julie A. Heath of Boise State University, was just published in the British Ecological Society’s Journal of Applied Ecology.
A key finding of the study was that American Kestrels nesting in close proximity to roads and developed areas had elevated stress hormones and high rates of nest abandonment – about ten times higher than kestrels in less-developed areas. American Kestrels are small, colorful falcons often seen perched along roadways and are abundant in urban and agricultural areas.
“In the case of the kestrel, the bird is possibly drawn into the urban environment by the abundant nesting and perching opportunities that environment provides and by the improved prey visibility provided by shorter grass. Unfortunately, this dynamic creates an ecological trap as ultimately the stresses caused by human activity lead the bird to abandon nests far more frequently,” said Heath.
The study involved the monitoring of 89 nest boxes along Idaho’s Interstate 84 (28 nests) as well as on posts and trees along secondary roads in other areas such as suburban (10 nests), rural-residential (24 nests), agricultural (22 nests) and shrubland (15 nests) in the breeding seasons of 2008 and 2009. Most (23 nests, 88%) of the nests that failed did so during incubation. Only three nests failed during the nestling stage. Sixteen of the 26 failed nests (62%) were abandoned.
The study says that cavity nesting birds, such as kestrels, who inhabit noisy environments may compensate for decreased auditory cues by increasing vigilance behaviour, such as visual scans from the nest entrance or flushing from the nest, leading to changes in energy allocation or extended periods away from the nest during incubation. This behavior appears to be followed, at a high rate, by nest abandonment.The researchers looked at corticosterone levels, which indicate degrees of stress – the equivalent of cortisol in humans. Corticosterone can lead to behavioral and physiological changes that enable individuals to cope with stressful situations, while suppressing other activities such as reproduction.
The data showed that female kestrels nesting in areas with high human activity, such as along noisy roadways, have higher corticosterone levels, but males do not. This could be because females spend more time in the nesting box and thus are exposed more often to stressors such as vehicle noise. These effects lessened the further a nest was from the road.
“Birds evolved in an environment that was not dominated by humans,” Heath noted. “In recent history, human roads and structures have left few areas untouched. We’re just starting to understand the real consequences.”
Given that the vast majority of land in the continental United States is within a mile of a road, wildlife increasingly are exposed to chronic levels of road noise. The resulting increase in stress levels could cause fundamental changes in physiology and behavior across species inhabiting human-dominated environments, which over time could lead to population declines.
As scientists continue to connect the dots between human disturbances and the resulting long-term effects on wildlife, changes already are yielding positive results. Research conducted in preserve areas, such as state parks, has led to reduced speeds and attempts to limit noise, although noise mitigation, while locally effective, may not protect widespread populations such as kestrels from the pervasive threat of traffic noise.
The study concludes that until regulations or economic incentives are developed to encourage engineering innovations that result in quieter roads, projects in areas of human activity with favorable habitat should be discouraged in order to decrease the risk of ecological traps.
According to Dr. George Fenwick, President of American Bird Conservancy, one of the leading U.S. bird conservation organizations, “Many people think that since they see certain species of birds in urban environments, that they must have adapted to those unnatural surroundings. This study certainly suggests that at least in some circumstances, the exact opposite is true. Birds are being lured away from their more natural environment, into areas where their ability to reproduce is clearly being compromised.”
Conservation Groups Call for Increased Protections for Rapidly Declining Seabird
(Washington, D.C., May 13, 2013) In a letter sent today, over 100 conservation and scientific organizations are calling on the Obama administration to provide new protective measures for the Marbled Murrelet, a federally listed bird species whose population is rapidly declining.
The letter asserts that the “accelerated decline of this species is an indication that current protections for its old-growth forest habitat need to be augmented, benefitting clean air, clean water, wild salmon runs, carbon sequestration, and other ecosystem services uniquely provided by these irreplaceable forests.”
A recent peer-reviewed study by the U.S. Fish and Wildlife Service and U.S.D.A. Forest Service found that the Marbled Murrelet’s population in California, Oregon, and Washington State had declined by 29 percent over the last decade. This trend is consistent with the government’s 2009 five-year status review of the species, which concluded the population could be extinct outside of the Puget Sound area within 100 years.
“More needs to be done. These findings indicate that current efforts to eliminate threats and protect habitat are not enough to bring this species back,” said Steve Holmer, senior policy advisor for American Bird Conservancy, a leading bird conservation group. “Additional habitat protection, acquisition of new forest reserves, and improved recreation management offer hope for its eventual recovery.”
Murrelet habitat on state and private lands continues to be lost to logging. One study (Falxa et al) documented a 30 percent loss of murrelet habitat on nonfederal lands within the tri-state range between 1996 and 2006. That same study recognized timber harvest as the primary cause of habitat loss on nonfederal lands.
Proposed changes to the Northwest Forest Plan have also left the species’ habitat more vulnerable to disturbance. The final 2012 Northern Spotted Owl critical habitat rule encourages logging in owl-critical habitat, which, in part, overlaps with that of the murrelet. Agency analysis included in the owl rule’s draft environmental assessment indicates that such management practices would likely be harmful to the Marbled Murrelet. Logging—both clearcutting and commercial thinning—increases fragmentation, opening the forests to nest predators such as crows, ravens, and jays.
“To conserve the murrelet, a plan is needed that will protect the remaining habitat and prevent fragmentation in nearby forests to minimize predation and nest disturbance,” said Holmer. “These steps would offer hope for the Marbled Murrelet, and help to preserve an ancient forest legacy for the benefit and enjoyment of current and future generations of Americans.”
4th July 2014