Don’t hike so close to me: How the presence of humans can disturb wildlife up to half a mile away


What are you looking at? Greg Shine, BLM/Flickr, CC BY

Jeremy Dertien, Clemson University ; Courtney Larson, University of Wyoming, and Sarah Reed, Colorado State University

Millions of Americans are traveling this summer as pandemic restrictions wind down. Rental bookings and crowds in national parks show that many people are headed for the great outdoors.

Seeing animals and birds is one of the main draws of spending time in nature. But as researchers who study conservation, wildlife and human impacts on wild places, we believe it’s important to know that you can have major effects on wildlife just by being nearby.

In a recent review of hundreds of studies covering many species, we found that the presence of humans can alter wild animal and bird behavior patterns at much greater distances than most people may think. Small mammals and birds may change their behavior when hikers or birders come within 300 feet (100 meters) – the length of a football field. Large birds like eagles and hawks can be affected when humans are over 1,300 feet (400 meters) away – roughly a quarter of a mile. And large mammals like elk and moose can be affected by humans up to 3,300 feet (1,000 meters) away – more than half a mile.

Elk viewed over a hiker's shoulder.
A hiker about 75 feet from a bull elk in Yellowstone National Park. Jacob W. Frank, NPS/Flickr

Many recent studies and reports have shown that the world is facing a biodiversity crisis. Over the past 50 years, Earth has lost so many species that many scientists believe the planet is experiencing its sixth mass extinction – due mainly to human activities.

Protected areas, from local open spaces to national parks, are vital for conserving plants and animals. They also are places where people like to spend time in nature. We believe that everyone who uses the outdoors should understand and respect this balance between outdoor recreation, sustainable use and conservation.

How human presence affects wildlife

Pandemic lockdowns in 2020 confined many people indoors – and wildlife responded. In Istanbul, dolphins ventured much closer to shore than usual. Penguins explored quiet South African Streets. Nubian ibex grazed on Israeli playgrounds. The fact that animals moved so freely without people present shows how wild species change their behavior in response to human activities.

Decades of research have shown that outdoor recreation, whether it’s hiking, cross-country skiing or riding all-terrain vehicles, has negative effects on wildlife. The most obvious signs are behavioral changes: Animals may flee from nearby people, decrease the time they feed and abandon nests or dens.

Other effects are harder to see, but can have serious consequences for animals’ health and survival. Wild animals that detect humans can experience physiological changes, such as increased heart rates and elevated levels of stress hormones.

And humans’ outdoor activities can degrade habitat that wild species depend on for food, shelter and reproduction. Human voices, off-leash dogs and campsite overuse all have harmful effects that make habitat unusable for many wild species.

Disturbing shorebirds can cause them to stop eating, stop feeding their young or flee their nests, leaving chicks vulnerable.

Effects of human presence vary for different species

For our study we examined 330 peer-reviewed articles spanning 38 years to locate thresholds at which recreation activities negatively affected wild animals and birds. The main thresholds we found were related to distances between wildlife and people or trails. But we also found other important factors, including the number of daily park visitors and the decibel levels of people’s conversations.

The studies that we reviewed covered over a dozen different types of motorized and nonmotorized recreation. While it might seem that motorized activities would have a bigger impact, some studies have found that dispersed “quiet” activities, such as day hiking, biking and wildlife viewing, can also affect which wild species will use a protected area.

Put another way, many species may be disturbed by humans nearby, even if those people are not using motorboats or all-terrain vehicles. It’s harder for animals to detect quiet humans, so there’s a better chance that they’ll be surprised by a cross-country skier than a snowmobile, for instance. In addition, some species that have been historically hunted are more likely to recognize – and flee from – a person walking than a person in a motorized vehicle.

Generally, larger animals need more distance, though the relationship is clearer for birds than mammals. We found that for birds, as bird size increased, so did the threshold distance. The smallest birds could tolerate humans within 65 feet (20 meters), while the largest birds had thresholds of roughly 2,000 feet (600 meters). Previous research has found a similar relationship. We did not find that this relationship existed as clearly for mammals.

We found little research on impact thresholds for amphibians and reptiles, such as lizards, frogs, turtles and snakes. A growing body of evidence shows that amphibians and reptiles are disturbed and negatively affected by recreation. So far, however, it’s unclear whether those effects reflect mainly the distance to people, the number of visitors or other factors.

Graphic showing distances at which human presence affects animals' behavior.
Human recreation starts to affect wild creatures’ behavior and physical state at different distances. Small mammals and birds tolerate closer recreation than do larger birds of prey and large mammals. Sarah Markes, CC BY-ND

How to reduce your impact on wildlife

While there’s much still to learn, we know enough to identify some simple actions people can take to minimize their impacts on wildlife. First, keep your distance. Although some species or individual animals will become used to human presence at close range, many others won’t. And it can be hard to tell when you are stressing an animal and potentially endangering both it and yourself.

Second, respect closed areas and stay on trails. For example, in Jackson Hole, Wyoming, wildlife managers seasonally close some backcountry ski areas to protect critical habitat for bighorn sheep and reduce stress on other species like moose, elk and mule deer. And rangers in Maine’s Acadia National Park close several trails annually near peregrine falcon nests. This reduces stress to nesting birds and has helped this formerly endangered species recover.

 

 

 

Getting involved with educational or volunteer programs is a great way to learn about wildlife and help maintain undisturbed areas. As our research shows, balancing recreation with conservation means opening some areas to human use and keeping others entirely or mostly undisturbed.

As development fragments wild habitat and climate change forces many species to shift their ranges, movement corridors between protected areas become even more important. Our research suggests that creating recreation-free wildlife corridors of at least 3,300 feet (1,000 meters) wide can enable most species to move between protected areas without disturbance. Seeing wildlife can be part of a fun outdoor experience – but for the animals’ sake, you may need binoculars or a zoom lens for your camera.

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Jeremy Dertien, PhD Candidate in Forestry and Environmental Conservation, Clemson University ; Courtney Larson, Adjunct Assistant Professor, University of Wyoming, and Sarah Reed, Affiliate Faculty in Fish, Wildlife and Conservation Biology, Colorado State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Headphones, saw blades, coat hangers: how human trash in Australian bird nests changed over 195 years


This, if you can believe it, is part of a magpie nest.
Kathy Townsend, Author provided

Kathy Ann Townsend, University of the Sunshine Coast and Dominique Potvin, University of the Sunshine CoastEnvironmental scientists see flora, fauna and phenomena the rest of us rarely do. In this series, we’ve invited them to share their unique photos from the field.


When we opened a box supplied by museum curators, our research team audibly gasped. Inside was a huge Australian magpie nest from 2018.

It was more than a metre wide and made up of the strangest assortment of items, including wire coat hangers, headphones, saw blades and plastic 3D glasses — a mix of detritus reflecting our modern lifestyle.

This was one of almost 900 Australian nest specimens dating back over 195 years that we inspected for our recent, world-first study.

We estimate that today, around 30% of Australian bird nests incorporate human-made materials (primarily plastics). We also noted a steady increase in nest parasites over this period.

It’s clear the types of debris the birds use has reflected changes in society over time. They highlight the unexpected and far-reaching ways Australians impact their environment, and put birds in danger.

The full magpie nest from 2018 that was collected outside a construction site.
Kathy Townsend, Author provided

The first synthetic item

Birds and humans have been sharing spaces and habitats throughout history.

It’s well known birds incorporate material from their environment into their nests, making them ideal indicators of environmental changes and human activity. It’s also well known, particularly among scientists, that museum collections can provide unique insight into environmental changes through time and space.

Compare the magpie nest above to this natural butcherbird nest from 1894. Butcherbirds are in the same family as magpies.
Dominique Potvin, Author provided

With this in mind, our international team investigated Australian museum bird nest specimens collected between 1823 and 2018. Sourced from Museums Victoria and CSIRO’s Crace Site in Canberra, we inspected a total of 892 nests from 224 different bird species.

Australian birds generate an amazing array of nest types. Rufous fantails, for example, build delicately woven structures made of fine grass and spiderwebs, while welcome swallows and white-winged choughs create nests out of mud, which dry incredibly hard and can be used year after year.

A woven egg cup nest from 1870, made of grass and spiderwebs, by the rufous fantail.
Kathy Townsend, Author provided
Fabiola Opitz, a member of our research team, measuring mudnest collected circ. 1933 of a whitewinged chough. These mudnests can last for years.
Dominique Potvin, Author provided

Before the 1950s, human-made debris found in the nests consisted of degradable items such as cotton thread and paper.

This changed in 1956, when we found the first synthetic item in a bird nest from Melbourne: a piece of polyester string. This appearance correlates with the increased availability of plastic polymers across Australian society, seven years after the end of the second world war.

Australian magpies earn their name

We also determined, based on collection date and using historical maps, whether the nests came from natural, rural or urban landscapes. And it turns out the nest’s location, when it was built, and the species that made it largely determined whether human-made materials were present.

Brown nest with blue string
The nest of a noisy miner found on the Sunshine Coast, Queensland, in 2020 with plastic string.
Kathy Townsend, Author provided

Our study found nests built close to urban areas or farmland after the 1950s by birds from the families Craticidae (Australian magpies and butcherbirds), Passeridae (old world or “true” sparrows) and Pycnonotidae (bulbuls) had significantly more human-made debris.

Familiar to many an urban bird enthusiast, these species tend to adapt quickly to new environments. The incorporation of human materials in nests is likely one example of this behavioural flexibility.

The research team also had access to ten bowerbird bowers from the family Ptilonorhynchidae, spanning more than 100 years. Male bowerbirds are known for creating elaborate structures, decorated with a range of colourful items to attract a mate.

A silvereye or gerygong nest from 2019.
Kathy Townsend, Author provided

In the 1890s, the birds decorated their bowers with natural items such as flowers and berries. Newspaper scraps were the only human-produced items we identified.

This changed dramatically 100 years later, where the most sought-after items included brightly coloured plastics, such as straws, pen lids and bottle caps.

A satin bowerbird collecting blue junk. Video: BBC Wildlife.

But there are tragic consequences

When birds weave non-biodegradable materials — such as fishing line and polymer rope — into their nests, it increases the risk of entanglement, amputation and even accumulation of plastics in the gut of nestlings.

For example, we found evidence of one pallid cuckoo juvenile dying in 1981 after it was entangled in plastic twine used by its adoptive bell miner parents.

This is the bell miner nest with twine that caused the cuckoo chick to die, according to the museum notes.
Dominique Potvin, Author provided

Plastic was not the only issue. We found the prevalence of nest parasites that attack the young chicks also increased by about 25% over the last 195 years.

Nest parasites can kill huge numbers of nestlings. Recent research into the forty-spotted pardalote in Tasmania, a threatened species, has shown nest parasites kill up to 81% of its nestlings.

What has caused this increase isn’t clear. However, the team determined it wasn’t directly linked to urban or rural habitat type, or the presence of human-made materials in the nest. This goes against the findings of other studies, which show a decrease of parasites in nests that incorporated items such as cigarettes.

Interestingly, we did find eucalyptus leaves might deter parasites, as nests that incorporated them were less likely to show evidence of parasitism.

An eastern yellow robin nest from 2003, with eucalyptus leaves, lichen, spider webs and no parasites. Eastern yellow robins are specialist nest builders that don’t tend to stray from using specific natural items.
Kathy Townsend, Author provided
This nest from 1932 is from an Australian magpie, using eucalyptus leaves.
Kathy Townsend, Author provided

It may be, therefore, that sticking with certain natural materials is not only better for the safety of nest inhabitants, but also may have an added effect of pest control.

Stop littering, please

While most are aware of how plastics harm sea life, our study is one of the first to show the impact goes further to harm animals living in our own backyard. If the trend continues, the future for Australian birds looks bleak.

However, we can all do something about it.

A weebill or mistletoe bird’s woven nest from 1941, with tufts of spider webs and plant fluff.
Kathy Townsend, Author provided

It is as simple as being responsible for our rubbish and supporting proposed legislation and campaigns for moving away from single-use plastics.

The team had access to nests from 224 different species, which equates to only about a quarter of Australia’s total of 830 bird species.

There is still plenty more to discover.




Read more:
Birds on beaches are under attack from dogs, photographers and four-wheel drives. Here’s how you can help them


The Conversation


Kathy Ann Townsend, Senior Lecturer in Animal Ecology, University of the Sunshine Coast and Dominique Potvin, Lecturer in Animal Ecology, University of the Sunshine Coast

This article is republished from The Conversation under a Creative Commons license. Read the original article.