Identifying minimum patch sizes for breeding success in birds

A new study illustrates the importance of understanding the minimum patch size that an at-risk bird needs to reproduce. Jerrod Butcher and fellow researchers from Texas A&M University looked at the effect of habitat patch size on two songbirds in north-central Texas.

For the federally endangered golden-cheeked warbler, they found that birds did not successfully breed in patches smaller than 15-20 hectares indicating that a threshold exists at that size below which the birds do not reproduce. However, the study also found that the warblers established territories in patch sizes as small as 2.9 hectares (the smallest studied) and paired in patches as small as 4.1 hectares.

From a conservation perspective, this study shows that research looking at just the presence-absence of the warblers (or even bird pairings) would substantially underestimate the minimum habitat patch size needed to sustain a viable population.

The researchers also looked at white-eyed vireos, a habitat generalist, and as predicted found no evidence of a minimum patch size threshold for breeding success - the vireos successfully reproduced in patches as small as 4.1 hectares.

One of the benefits of identifying patch size thresholds is that by looking at how different environmental variables change when you cross the threshold, you can get clues on what factors are influencing the bird behavior. In this vein, the researchers looked at two variables along the patch size gradient: 1) brown-headed cowbird parasitism; and 2) abundance of arthropods - the food source for the birds.

However, the researchers found no relationship between either variable and patch size, which means they likely are not explanations for the threshold. So more research is needed to figure out why golden-cheeked warblers do not breed in patches smaller than 15-20 hectares.

This study also raises the issue of whether small patches act as ecological traps for the golden-cheeked warblers resulting in population sinks that further threaten the species. This could occur if small patches are attractive to the warblers leading to numerous small territories where the birds are not able to reproduce. However, the study authors warn against jumping to that conclusion. They write,

"Patches of habitat less than 20 hectares in area may not be large enough to sustain a viable population of golden-cheeked warbler in the long-term; however, such patches may benefit populations if the patches can sustain breeding pairs in the short term."

Nevertheless, they advise that managers across the distribution range of golden-cheeked warbler be cautious about decreasing vegetation patches below 20 hectares. Similar research on minimum patch-size thresholds for breeding success could be important for the conservation of other at-risk birds.

--Reviewed by Rob Goldstein--Conservation Maven

Butcher, J., Morrison, M., Ransom, D., Slack, R., & Wilkins, R. (2010). Evidence of a Minimum Patch Size Threshold of Reproductive Success in an Endangered Songbird Journal of Wildlife Management, 74 (1), 133-139 DOI: 10.2193/2008-533

State endangered-species lists are failing to protect species that need help the most

A new analysis of birds on state endangered species lists suggests that some species receive insufficient protection while others are receiving protection unnecessarily.

This may be attributable to the fact that state endangered species lists are composed by policy process rather than by scientific process.

Birder's World has a good article highlighting the new analysis.

You can also find the analysis, by Jeff Wells of the Boreal Songbird Initiative, at PLoS ONE.

In Ohio, the following species are listed as endangered (e) or threatened (t) though their listing could be considered questionable based on the new analysis. Many of the species on these lists are based on local rarity and rarity is prioritized, however rarity may be detrimental to conservation efforts.

-Yellow-bellied Sapsucker(e): Primarily migratory(2) through Ohio with a resident population estimate in the state of about 400 birds, while the global population estimate is 9,000,000 individuals (1).

-Loggerhead Shrike (e): The global population for this species is estimated at 4,200,000 individuals while Ohio's estimated population is roughly 300 individuals(1). Loggerhead Shrikes invaded Ohio in the mid-1800's as deciduous forests were replaced by agricultural fields and then declined by the 1930's (2).

-Lark Sparrow (e): a species that spread into Ohio in the 19th century as land use became primarily agricultural. Their occurrence in the state was sparse and varied from place-to-place until in the 1960's they were restricted to the Oak Openings preserve near Toledo, Ohio (2). Peterjohn suggests that at most Ohio hosted about 12 breeding pairs in the Oak Openings region (2), while the global population estimate is 9,900,000 individuals (1).

-Dark-eyed Junco (t): The global population estimate for this species is 260,000,000 whereas(1) the Ohio breeding population is roughly 30-50 individuals(2).

Some species should probably be given greater priority given that Ohio hosts a relatively large portion of the global population of these species.

-Cerulean Warbler is considered a species of concern in Ohio, however the global population for this species is estimated at 560,000 individuals (1). Ohio hosts an esitimated 70,000 breeding Cerulean Warblers, or ~13% fo the total population(1). Ohio's role in the management of this species is potentially great and proper habitat management may bolster global population numbers.

-Henslow's Sparrow, an Ohio species of concern, hosts an estimated population of 6,000 individuals or ~7.5% of the global population of 80,000.

While some birders and state naturalists may be inclined to disagree with this new analysis, because it may impact their state lists, the proposal of species listing and management based on a more scientific process should result in more efficient and cost-effective management practices.


1 Partner in Flight Landbird Population Estimates Database, Version 2004

2 Peterjohn, B. G. 2001. The Birds Of Ohio. The Wooster Book Company. Wooster, Ohio.

Arctic Terns Longest Migrants....Still

By HENRY FOUNTAIN
NY TIMES

To reach elite status in many airline frequent-flier programs, you have to log at least 50,000 miles in the air in a year.

Somewhere in Greenland there’s an Arctic tern that could qualify.

Arctic terns have a reputation as long-distance travelers, migrating to the Southern Ocean from breeding grounds in the Arctic. Researchers have suggested the round-trip distance might be as much as 25,000 miles.

But those were only estimates. While location-tracking tags have been used with large birds like albatrosses, Arctic terns, at less than four ounces, were too small to carry them.

Now Carsten Egevang of the Greenland Institute of Natural Resources and colleagues have devised a miniature data logger that, at 1/20th of an ounce, is light enough. It records light intensity, using the timing of sunrise, sunset and length of twilight to determine latitude and longitude.

In The Proceedings of the National Academy of Sciences, the researchers report on the journeys of 11 terns fitted with the devices. The birds, which began their trips in Greenland or Iceland in August, took two routes south, some hugging the African coast and others crossing from West Africa to Brazil to follow the South American coast. They stopped for about three weeks in the mid-Atlantic east of Newfoundland, a rich feeding zone.

Once they reached the Southern Ocean, they spent four months flying primarily east and west, again in areas that are rich in food. They returned in May and June having traveled, on average, about 44,000 miles. One tern totaled 50,700 miles, which is the longest animal migration ever recorded electronically.

Can restoration be too small? Negative effects on avian behavior...

Many conservation practitioners operate with a common assumption that all ecosystem restoration is good no mater the size of the project area. A new study in the Journal of Applied Ecology contradicts this notion by showing that when it comes to tropical reforestation and the effect on birds, bigger is better and too small may be bad.

The work by Emily Morrison and fellow researchers is groundbreaking not just because it shows the importance of patch size in restoration but because it looks at animal behavior to reach its conclusions. Most studies evaluate restoration success with birds by looking at metrics like species diversity.

This study though looked at just four birds - cherrie’s tanagers, rufous-capped warbler, common tody-flycatcher and plain wren - and compared their insect foraging behavior across restored forest patches of different sizes.

They found that in the smaller patches the birds attacked insects at a lower rate (i.e fewer attacks per minute) and exerted more effort while foraging (i.e more jumping around). They also found that arthropod density was nearly twice as great in larger reforestations (greater than 3500 square meters) than smaller ones (less than 350 square meters).

Together these results indicate that birds in the smaller patches are having a more difficult time foraging for food which may have negative consequences for their fitness. This in turn may impede restoration success given that birds in the tropics play an important role in a number of ecosystem processes such as pollination and seed dispersal. Interestingly, a more conventional assessment looking at just species diversity likely would not have picked up on this problem.

These results have practical applicability because conservationists - whether in the tropics or elsewhere - are constantly weighing restoration size against project cost. Obviously, much more research is needed to determine how widely these results translate to other settings. In the case of tropical forests the authors recommend,

"Thus, forest restoration efforts using a patch-based planting scheme should consider patch size as an important factor that is likely to affect the quality of the patches as habitat for birds that use woody habitat. We recommend that small patches be avoided and that patches of at least a few thousand square metres be planted when resources are available."

--Reviewed by Rob Goldstein

Morrison, E., Lindell, C., Holl, K., & Zahawi, R. (2009). Patch size effects on avian foraging behaviour: implications for tropical forest restoration design Journal of Applied Ecology

Birdsongs provide population clues

Microphone array improves estimate of Ovenbird density.
Emma Marris

Published online 27 November 2009 Nature doi:10.1038/news.2009.1112

As any birder will tell you, most birds in the forest are easier heard than seen. Now two scientists have figured out a way to estimate bird population densities by recording their songs with an array of microphones.

The method offers an alternative to a common way to estimate population densities: the human ear. Humans listeners are often used in bird studies, but people are far from perfect, says Murray Efford of the University of Otago in Dunedin, New Zealand. In particular, "we aren't good at telling how far away sounds are," he says.

Efford and Deanna Dawson of the United States Geological Survey in Laurel, Maryland, have come up with a method that uses multiple microphones scattered through the woods. By recording in several places simultaneously, researchers can estimate each bird's acoustic 'footprint' — the area around it where it can be heard.

The size of the footprint depends on parameters such as the loudness of the birds and the acoustic properties of the forest. So Efford and Dawson must try different values for such parameters until they find a good match with the data recorded by the microphones. When all is done, the duo can estimate bird density without knowing the birds' locations or the size of the forest.

Twitter tweet!

They tried out their method on ovenbirds (Seiurus aurocapilla) at the Patuxent Research Refuge near Laurel, Maryland. Only male ovenbirds sing, and the technique estimated their density at around one male bird per every five hectares (click here to hear the ovenbird's song). The findings matched well with estimates gleaned from catching the little songbirds in nets. What's more, the researchers found that the new technique was more precise than estimates based on netting. The work is published online in the Journal of Applied Ecology1.

The researchers say that the method could be used to estimate densities of other hard-to-spot animals, including whales and dolphins. Len Thomas, a statistical ecologist at the University of St Andrews, UK, for instance, is already using a similar method as part of an effort to monitor Minke whales (Balaenoptera acutorostrata) by their sounds. Sightings of these whales in the Pacific can be counted on one hand, but males make a distinctive "boy-yoy-yoing" sound, so hydrophones can measure their song footprints, just like the ovenbirds.

However, Thomas says that Efford and Dawson's method only provides part of the picture for Minke populations. The method estimates only the densities of sounds, not of animals, and in the case of the whales, uncertainty about what percentage of males call and how often they do so make it hard to extrapolate to an estimation of the population density.

Efford adds that the new technique will work best with animals that make repetitive sounds at constant loudness. That means it could be especially useful for estimating population densities of other kinds of birds. "A lot of birds are blurting out the same thing over and over again, persistently and monotonously," he says.

The monotony may have gotten to Efford, after listening to ovenbird songs over and over for the study. "It is a particularly irritating and insistent call," he admits.

References
Dawson, D. K. & Efford, M. G. J. Appl. Ecol. 46, 1201-1209 (2009).

Native Garden Workshop--3.28.09 @ Aullwood Audubon Center & Farm

When I was child I watched an old black-and-white horror film called “The Day of the Triffids.” It was about deadly alien plants from outer space, called triffids, which come to earth to kill humans; most of who were blinded by the lights of a meteor shower that brought the triffids to our planet and could not see the approaching threat until it was too late. That movie terrified me back then.

Imagine my surprise then when I grew up and learned that there were real invading, killer plants spreading across our world; their spread being blindly aided by humans who helped move the plants from place-to-place and habitat-to-habitat, and in many cases were intentionally planting them.

Of course the real invaders are not aliens from a different planet, but from right here on earth, and while these alien invasive plants are not necessarily chasing down and killing humans they are causing the deaths of many plant and animal communities around the globe.

Many common invasive plants started out innocently enough as beautiful ornamental plants used for landscaping, or as potential food and medicinal purposes. In many cases, the U.S. Government was responsible for the spread of many of invasive plants in the U.S.

When “The Day of the Triffids” was released in 1962 it had been almost thirty years since the severe drought and the resulting great dust storms had spread beyond the Dust Bowl region of the country resulting in the collapse of the U.S. agriculture system and economic hardship for much of the country. The U.S. government stepped in with innovative programs to stabilize both agriculture and the economy. One of those programs was the Soil Erosion Service, which transformed into the Soil Conservation Service, and is known today as the U.S. Department of Agriculture’s Natural Resource Conservation Service. The Soil Conservation Service, like its name suggests, was tasked with revising agricultural practices at the time to conserve and prevent the further loss of top soil in Midwestern farm states like Wisconsin. The Service developed a variety of beneficial farming practices to reduce erosion, like terracing and contour cropping. Another practice the Service developed was the creation of wind rows and plantings for wildlife food and cover, which were comprised of fast-growing plants with spreading roots to hold soil in place, and potential food crops, like berries, that might benefit a variety of wildlife. Some of these plants that were promoted included Multiflora Rose (Rosa multiflora), honeysuckles (Lonicera spp.), and privets (Ligustrum spp.).

Today, we are paying the price for the decisions of our past, both economically and ecologically. Researchers with Cornell University estimate that $120 billion are spent annually on economic losses and environmental impacts due to all invasive animals, plants, and microorganisms in the U.S.

There are an estimated 17,000 native plant species in the U.S., and many many more that are considered introduced. Of the introduced plant species in the U.S. approximately 5,000 have escaped and become invasive in natural habitats. $100 million/yr is spent on controlling these invasive plants in the U.S. In agricultural systems invasive weed plants contribute to nearly $24 billion in crop losses every year, another $1 billion annually on forage losses in pastures, and ranchers spend an estimated $5 billion/yr controlling weeds that may be toxic to cattle in pastures and ranges. In residential areas it’s estimated that $500 million are spent annually by homeowners to control invasive weed species in lawns and landscaping, and $1 billion is spent on weed control management on golf courses.

While there has been much research on the impact of invasive plants on native plant communities, we are beginning to gain a better understanding of how invasive plants are impacting animal communities. Birds, which share close relationships with plants, may face the greatest danger posed by invasive plants.

To learn why and how you can start using native plants in your landscaping projects consider attending the Native Gardens Workshop at Aullwood Audubon Center & Farm on March 28th, 2009. You can get more details and register for the workshop by contacting Aullwood directly.

Protecting Habitats While Fighting Climate Change

A new statement issued by the National Audubon Society reports that over the last 40 years 177 bird species have experienced range shifts northward during the winter, potentially as a result of climate change. On average, ranges have shifted by at least 35 miles, however at least 60 species are reported to have experienced range shifts of over 100 miles or more. The study is based on citizen science data collected during the organization’s annual Christmas Bird Count.

This report comes only weeks after another report issued by the National Oceanic and Atmospheric Administration (NOAA) that concluded that climate change will be largely irreversible for at least 1000 years after all carbon emissions are completely halted, based on current emission projections.

While many are promoting legislative action to reduce carbon emissions, the question remains whether legislation will be enough to truly make a difference. While there is no doubt that there is need to regulate the reduction of carbon emissions, achieving meaningful permanent regulation will be difficult.

Competing interests between environmentalists, agencies, energy producers, and other stakeholders will make it difficult to reach an agreement that is mutually beneficial environmentally and economically. Additionally, as we’ve seen with the weakening of many important environmental policies in the past several years, legislation is prone to short lifetimes as political administrations come and go.

Fortunately, there are possible solutions that may actually help. Preservation and creation of green spaces, like forests and grasslands, may help sequester atmospheric carbon and act as carbon sinks while also serving as habitat for birds and other wildlife.

Likewise, understanding how birds utilize different areas will be important for understanding how to prioritize efforts to protect and restore critical habitats that can also serve as carbon sinks.

A report that appeared in Science this week brings new hope to conservationists about the possibility of understanding bird movements during migration. Researchers with York University have used mini tracking devices have been able to track the movements of Purple Martins and Wood Thrushes throughout their migration. While the sample size was small, what they found was that stopover habitats for some species may be more critical than for others, especially for species experiencing dramatic population declines.

Conserving bird habitats and fighting climate change are not mutually exclusive activities, but it’s going to take more than just signing petitions and promoting legislation to make a substantial change. We will need to be more proactive in preserving and restoring habitats through efforts at many levels to protect the bird species that we love in the short term and to reduce the impacts of climate change in the long term.

Holiday Gift Ideas for Bird Conservationists

The onslaught of the holiday shopping season has begun and you might be wondering what gift is just right for a loved one. Save yourself some time and energy and use the American Avian Conservation Association’s holiday gift guide below to help you choose the perfect gift for the birdwatcher in your life.

•Bird-feeders and bags of bird-seed are always appreciated by novice and expert birdwatchers alike. A standard hopper feeder is always a safe bet, but if you're more familiar with feeder types you may want to try platform feeders for ground-feeding birds, like sparrows and dove, or more specialized feeders like those designed specifically for finches. Droll Yankee makes quality feeders. For a unique and whimsical gift, a bird-seed wreathe can be a great holiday gift. Pipestem Creek is one such company that makes some beautiful and functional wreaths that can provide a unique holiday accent to your home and feed the birds at the same time.

•Nest boxes can provide opportunities for entertainment and learning for birdwatchers; young and old alike. If your birdwatcher lives in a city or suburb you might try purchasing a wren or chickadee nest box for them. The smaller holes of these boxes make it difficult for non-native House Sparrows, which are often abundant in human habitats, to gain access to them. For more rural homes a bluebird box or even a Screech-owl box can make a wonderful gift.

•Books are valuable tools for people looking for tips and techniques on everything from choosing seed and feeder types, to building and installing bird houses, to choosing landscaping plants to attract birds. Look for them in your local bookstore.

•Gift memberships to bird conservation organizations can make a wonderful gift because the recipient can join a local and nationwide network of people who share their passion about the conservation of birds and other wildlife. You also have the satisfaction that your gift is going to support the work that these organizations do to protect birds and their habitats.

•A gift that is both an attractive piece of art and supports conservation is a habitat stamp. The Migratory Bird Hunting and Conservation Stamp (a.k.a. "The Duck Stamp") can make a wonderful gift for the birdwatcher in your life. $0.98 of every dollar spent on a "Duck Stamp" goes into leasing or purchasing land in the National Wildlife Refuge System, which provides critical habitat for many species of birds throughout the country. "Duck Stamps" are so named because they often depict species of waterfowl. Art for the stamps are chosen through a competitive contest. The stamps can be purchased in most post offices and outdoor sporting goods stores. You can get more information about how to purchase a stamp at 1-800-782-6724.

•Gift certificates to native plant nurseries can be a great gift for someone who likes to garden or landscape for birds, butterflies, or other wildlife. Native plants are better for birds for a variety of reasons, including as a more nutritious food source and safer nesting habitat.

•If your birdwatcher enjoys a good cup of coffee in the morning while checking out the birds on their feeders, you might want to consider purchasing some bird-friendly coffee for them. Bird-friendly coffee is grown in a manner that both preserves habitat for migratory and resident birds in central and South America, and does not involve pesticides and fertilizers. As a result the coffee is often certified as being organically grown. You can usually find bird-friendly coffee in the organic section of your local grocery store or your favorite local bird-specialty store. For a great-tasting bird-friendly coffee check out Good Migrations coffee. Learn more about bird-friendly coffee for birds by visiting the Coffee and Conservation web-site.

•For the high-tech birdwatcher an mp3 player with portable external speakers can be a good way of cataloging and condensing all of those bird song cds into one spot for quick reference. BirdJam customizes Apple iPod mp3 players with bird song cds and software already loaded and organized for quick and easy playback. These can be a great tool for helping someone learn their bird song identification.

•On those days when the weather is less than cooperative and the birds have sought shelter elsewhere, a good bird DVD might be in order. Popular movies like "Winged Migration," "March of the Penguins," "The Wild Parrots of Telegraph Hill," and “Happy Feet” can provide hours of learning and entertainment. Other movies like the 10-part documentary "The Life of Birds" by David Attenborough can be a great source of information about the ecology and identification of birds.

•For a truly unique and memorable gift for the birdwatcher in your life a bird-watching eco-tour vacation might be in order. Bird-watching eco-tours can be a great way to explore the world, see birds as well as other wildlife, learn about new cultures, and support the protection of natural habitats. National Geographic offers a wide array of tour destinations with a variety of different purposes.