Learning to Recognize Predators

A recent study found that migratory songbirds can learn from local resident birds when they reach unfamiliar territory for the first time. In particular, birds need to learn which predators to avoid.

The research team tested whether migratory songbirds observe the anti-predator behaviour of local birds, which are familiar with local predators. One common form of this self-protecting behaviour is "mobbing": The birds approach a potential predator, rapidly changing position around its location and performing restless wing and tail movements while emitting loud, broad-frequency calls. These calls are easily recognizable and act as signals of threat.

Because migrating birds rarely participate in mobs, the researchers speculate that they may gain information about predator location, identity and degree of threat through listening to mob calls of other species residing in the area. To test this theory, they broadcast playbacks of alarm calls that were familiar (black-capped chickadee, common in North America) and foreign (blue-gray tanager, common in Central America) to birds migrating between Canada and Belize.

The Belizean resident birds responded only to the tanager calls, but migrant birds responded to both the tanagers and the chickadees.

You can find the full paper online here (subscription required).

There remains some research to demonstrate the hypothesis; the research team still wants to test the reaction of migrant birds wintering in Belize against the behavior of those same migrants along their fall migration path. Still, this is an intriguing result. It is one more reason why it is silly to use "bird brain" as an insult. Animals have much better learning capabilities than many people realize.

A question that frequently arises among birders is what happens to vagrant or extralimital birds when they fly off course. Some hold that their lives are nasty and short; others point to examples of rare birds persisting for long periods at a single location. (I tend to fall into the latter group, though I can see arguments for both.) If migrants can observe the behavior of local birds and learn from them, it provides some hope that vagrant birds might be able to do so as well.

EPA Email / Exxon

In this Daily Show segment, Jon Stewart reports on the ignored email story from last week. If the embedded video does not work, try here. In addition, John Hodgman comments on the oil addiction.

Bird Diversity and the West Nile Virus

Last week, PloS ONE published an interesting paper that argues that a diverse bird population lowers the human risk of contracting the West Nile Virus (WNV). The study compared WNV infection rates in sixty-five pairs of neighboring counties, in which one county had human WNV infections and the other did not, while both had infected birds. (One of the pairs included my home county, Middlesex, and its neighbor to the west, Somerset.)

The paper measured the inter-county contrast in human infection rates against the contrast in various measures of avian biodiversity. (Bird population data was derived from the Breeding Bird Survey.) It found that greater bird diversity correlated with fewer human infections. Avian biodiversity explained about 30% of the contrast.

The reason is something called the "dillution effect," which was first observed with Lyme disease transmission. The mechanism for the dillution effect is unclear; none of the proposed mechanisms matched up with the data in this paper's analysis. However, it seems to be related to the greater relative abundance of species that are poor hosts for the disease compared to species that are more susceptible. In the case of WNV, highly-susceptible species such as crows and robins tend to predominate in areas of lower bird diversity, so the disease will have plenty of hosts and a greater likelihood of spreading beyond birds.

Here are a few interesting points from the analysis:

1. The analysis confirms that robins play a role in spreading WNV to humans. This has been reported in other studies, including one in Washington.
2. Unsurprisingly, corvids (crows, jays) are associated with human infections.
3. Surprisingly, finches also seem to be associated with human cases of WNV. I had not heard of finch susceptibility before reading this paper.
   
4. Passerines as a group appear to be resilient in the face of WNV outbreaks, at least in the initial stages of an epidemic. This seems to contradict some previous reports, but perhaps not. The authors suggest that many passerine species may be poor hosts.
   
5. Non-passerines seem much more susceptible to WNV than previously thought, so there may be many susceptible host species outside of Passeriformes.
   

As Mike wrote, studies like this provide us with a self-centered rationale for maintaining a diverse avian population. When we promote wildlife conservation, we are also promoting our own health.

From my own persepective, it may support conserving wildlife within cities as well as outside of them. Many environmentalists and urbanists argue that urban parks should not be wildlife habitat and should be for people instead. (I do not think those goals are always in conflict, but the argument exists.) This paper provides an example of how increasing local biodiversity can be beneficial to humans in concrete ways. In the case of WNV, the dillution effect works independently of relative urbanization. This suggests that perhaps a diverse wildlife population should have a place in urban planning.

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Blog Note: I will not have internet access for the next few days, so I have prepared several posts to publish automatically. (If you do not know how to schedule posts, see here.) Though the blog will have the regular posting schedule, I will not be able to respond to comments or email until later in the week.

Everglades Funding

Last week, when Florida announced that it would buy U.S. Sugar properties in South Florida, it seemed to me that some things were being left unsaid in the initial wire reports. I was particularly concerned with the funding for the purchase, and wondered if any other problems were lurking. (Yes, the last eight years have made me very cynical, indeed.) It turns out that funding is a problem in the Everglades deal.

But the deal will also tie up much of the state's share of Everglades funding -- at a time when budget worries have delayed other projects in the restoration plan. Federal funds have been so scarce that the U.S. Army Corps of Engineers, which is co-managing the restoration, has been ordered to slash project costs.

The state typically spends about $325 million a year on Everglades projects, said Tom Olliff, the district's assistant executive director. But the debt payments on the $1.7 billion sugar deal will eat up as much as $153 million of that each year.

The water district should still have about $170 million a year to spend on other Everglades projects and land purchases, Olliff said. But some of that money must be approved annually by the Legislature, which cut Everglades funding for the budget year that begins Tuesday.

No one has drawn plans for building on the U.S. Sugar property, but any combination of new reservoirs and marshes would certainly add billions of dollars to the price tag. For example, a 16,000-acre Everglades reservoir under construction in Palm Beach County is expected to cost taxpayers about $800 million.

Restoration of natural flow from Lake Okeechobee to Everglades National Park also seems unlikely, despite initial reports.

''It's a lovely concept,'' said Carol Ann Wehle, the water management district's executive director. But ``you are never, ever going to have sawgrass marsh there.''

Planners say the sugar fields south of the lake have lost too much earth to farming, leaving a deep bowl that would prevent any water from flowing to the south without artificial pumps. Studies also have shown that converting the sugar fields to marsh would produce so much evaporation that the Everglades could wind up with less water.

In any case, Lake Okeechobee's water is simply too polluted to pour directly into the Glades. A reservoir would allow water managers to manipulate water depths and move it where it's needed depending on rainfall and seasonal conditions.

There are other issues as well; in particular, indigenous tribes living in the area do not seem to have been consulted by the state. There is plenty more discussion at the link.

The deal was still worth doing, even if it temporarily stops some of the other restoration projects. U.S. Sugar's cessation of operations will remove at least one major water user and polluter. That seems to be a step in the right direction, even if its potential takes a long time to be realized.

The Canary Effect

Last year, lead dust in the town of Esperance, Australia, killed 4,000 birds. The dust's source was a shipment of lead from Magellan Metals' Wiluna mine that passed through Esperance. A year later, the problem persists.

Dr Nic Dunlop, who contributed to the study, says it found most birds recorded lead levels 10 to 100 times higher than normal.

He says the contamination is likely to cause more bird deaths.

"Now the problem is over time, they will increasingly ingest that lead, either through preening or through their food, so it's quite likely as time goes on that we will get a second wave of impact on birds and other wildlife as a consequence of that lead," he said.

The Planning and Infrastructure Minister Alannah MacTiernan says the study is outdated.

She says the Government is constantly monitoring lead levels in the area.

"Since then we have done another comprehensive clean up at the port and since then all of the other tests that we have done all of the tests, November, December, January, February, March are all showing improvements in the outcomes in fact quite dramatic improvements," she said.

It is a very sad situation, and one that must be unsettling for the town's residents. So far I have not heard about any human casualties from lead pollution in Esperance, but I am sure that it is having an effect – if not among adults then among children. This is one reason that it is good to keep birds around: they are much more sensitive to changes in the environment, and sound the alarm when something is wrong.

Interview with Barbara Boxer

Last night Bill Moyers interviewed Senator Barbara Boxer (D-CA) on the Bill Moyers Journal. The segment covers the 20th anniversary of James Hansen's initial warning about climate change in 1988, Boxer's conflicts with Senator James Inhofe (R-OK), and the recent demise of the Lieberman-Warner Climate Security Act.

Unfortunately PBS does not make it possible to embed its videos, so you will have follow the link to the PBS website to watch it.

Why Migration Changes Matter

In yesterday's Loose Feathers, I linked to a story about how migratory birds have adjusted to climate change (or not, in some cases), according to the records at the Manomet research station. Basically, the short-distance migrants, like swamp sparrow, were able to adjust their schedules to keep pace with a warmer climate because the temperatures on their wintering grounds are pretty similar to the temperatures at Manomet, and follow similar cycles. Meanwhile, the long-distance migrants, like great-crested flycatcher, winter in the tropics and do not have the same temperature cues as a bird in the temperate zone. So they have not adjusted their schedules.

The reason this is important is that a warming climate is also changing what the birds will find when they get to their destinations. Consider the following two news reports, both issued yesterday.

First, the types of fish prevalent in Narragansett Bay and Rhode Island Sound have changed over the past fifty years.

According to Jeremy Collie, professor of oceanography at the University of Rhode Island's Graduate School of Oceanography, the fish community has shifted progressively from vertebrate species (fish) to invertebrates (lobsters, crabs and squid) and from benthic or demersal species -- those that feed on the bottom -- to pelagic species that feed higher in the water column. In addition, smaller, warm-water species have increased while larger, cool-water species have declined....

"While we're catching more fish now, we're also catching smaller fish," said Collie, "and that corresponds with how the preferred temperatures of the fish here have changed. The fish community now is dominated by warm-water adapted species compared with what we started with, and fish that live in warmer water are smaller."

Collie added that fishing may also be a factor in the decline in fish size, since fishing removes the largest individuals from a population while leaving the smaller ones. However, he believes that climate is "the dominant signal." Sea surface temperature in the area of the trawls has increased by 2 degrees Centigrade since 1959, and the preferred temperature of the fish caught in the trawls has also increased by 2 degrees C.

Second, plants in Europe are climbing mountains at a rate of 29 m per decade.

Professor Lenoir, an ecologist at AgroParisTech, France, said the team wanted to establish whether "fingerprints of climate change were already apparent in ordinary ecosystems".

In order to do this, the team of French and Chilean researchers compared the distribution of forest species between 1905 and 1985 with their distribution between 1986 and 2005....

"We used 171 species commonly found over French mountains, which are part of Mediterranean, temperature and mountainous forest ecosystems between 0m to 2,600m above sea level.

"We found a significant change in species' altitudinal distribution towards higher elevation of about 29 metres per decade.

"Out of the 171 species, most are shifting upwards to recover temperature conditions that are optimal for their development and reproduction."

These may serve as examples of how local ecosystems are changing rapidly in the face of warmer climates. Similar trends occur in phenomena more closely related to the timing of bird migration. A warmer spring may prompt plants to sprout, flower, and leaf more quickly. This in turn will affect any associated insects – either pollinators or leaf-eaters. The insects will either hatch and breed earlier, or keep to their schedules and have less to eat as a result.

Birds that time their migrations to take advantage of floral nectar (hummingbirds) or abundant insects (flycatchers and other insectivores) will find food scarcer than it used to be. Flowers and insects may already be past their peak by the time the birds arrive. Adjusting their migration schedules is absolutely crucial to their survival in a warmer climate.

Loose Feathers #155

California Quail / Photo by Lee Karney (USFWS)

Bird news

• A paper in Science may make our field guides obsolete. Genetic analysis by the Early Bird project of 169 bird species, representing all major groups, revealed that much of current bird taxonomy is wrong and that many bird groups that appear to be similar evolved separately. For example, falcons are more closely related to parrots and songbirds than to hawks and eagles. The most thorough account of the findings that I have seen so far is at Living the Scientific Life. Science Daily has a good write-up, too. National Geographic illustrates some of the new sister clades.
• Scientists at Manomet on Cape Cod analyzed data for 32 bird species and found that eight of them migrated past the observatory much earlier than they did 38 years ago. These eight are short-distance migrants coming from elsewhere in the U.S. and can adjust their migration schedules to keep up with earlier springs. Birds that winter in Central or South America have not adjusted as well because they do not have the same temperature cues.
  
• A preliminary study in 2007 at Judith Gap Wind Energy Center found 1,206 bats and 406 birds died from turbine-related causes. The wind farm is the largest in Montana. ABC has a round-up of recent work on mitigation measures to prevent wind farm deaths.
  
• Agribusiness and ethanol lobbyists are pushing the federal government to allow farmers to plant corn on land that is currently in the Conservation Reserve Program. The CRP is the largest federal land conservation program and benefits many species of birds.
• White storks have benefited from a reintroduction program in Alsace and Lorraine. Twenty-five years ago, only 9 stork pairs were left in the Upper Rhine Valley; now there are 270 pairs.
  
• Eight captive California condors had to be evacuated from the Ventana Wildlife Society due to a nearby wildfire.
• The white-winged flufftail is an endangered species about which little is known, including whether it migrates. The lack of information frustrates conservation action plans.
  
• The RSPB is working with hunting groups to reduce raptor killings on private lands.
• Illinois is re-evaluating its state list of threatened and endangered species.
• The Guardian has a gallery of the most aggressive birds.
• Another gallery shows a heron grabbing and eating a duckling.
  
• Here is a profile of the naturalist at Cheesequake State Park (New Jersey).
• The CLO has free resources available for teachers and parents who want to do citizen science projects in urban areas.
  

Birds in the blogosphere

• Bug Girl: Aquatic Mercury in Food webs
• Picus Blog: Mississippi Kites in Newmarket, NH
  
• Rigor Vitae: English Sparrow Update (on predation by other birds)
• 10,000 Birds: Green Herons and their Groovy Necks
• Ecobirder: Yellowstone Barrow's Goldeneye
• Birdfreak: Bird Conservation - Prothonotary Warbler
• BES Group: White-throated Kingfisher: Non-iridescent colours
  
• Birds and Things: English Sparrows Seen As A Nuisance
• Zen Birdfeeder: Adirondack Loon Census July 19th (volunteers needed!)
  

Environmental news

• California has announced a plan to cut state greenhouse gas emissions to 1990 levels by 2020.
  
• Brazil seized 3,100 cattle that were grazing on illegally-cleared rainforest land.
• A sugar cane biofuels project in Kenya threatens to destroy the country's most diverse wetlands. The Tana Delta wetlands are home to 345 species of birds and support the livelihoods of thousands of farmers and fishermen.
• One result of Florida's purchase of U.S. Sugar lands is that it removes a political obstacle from Everglades restoration.
  
• A proposed coal-fired power plant in rural Virginia has drawn heavy opposition from residents.
• A study of the impact of acid rain on microorganisms in Adirondack lakes found that high acidity reduced overall bacterial diversity, but increased some rarer forms of bacteria.
• According to the Energy Information Administration, expanding offshore drilling would do little to change gasoline prices.
  
• James Hansen: Twenty Years Later
  

Carnivals and newsletters

• I and the Bird #78
• Tangled Bank #108
• Carnival of Environmental Issues #24
  
• Birds in the News #136
  

I and the Bird

The latest I and the Bird is online at It's Just Me.

How Singing Helps Warblers Find Breeding Habitat

Spring is accompanied by an explosion of birdsong that lasts well into the summer. Every morning for the past few months I have woken to the sound of a catbird singing outside my window. We are all familiar with the role birdsong plays in the early breeding season. Males sing to win and defend their territories and, in turn, attract females to mate with them. As the breeding season progresses, continued singing by adults helps juvenile birds learn to sing. It turns out that late season singing has one more function: it helps fledglings find appropriate breeding habitat for the following year.

That was the conclusion of a recent study involving one of my favorite birds, the black-throated blue warbler (Dendroica caerulescens). The researchers wanted to test whether social cues, such as late season birdsong or the presence of fledglings, helped other birds determine which sites had the best potential for breeding.

They set up 54 test sites in White Mountain National Forest in places with inappropriate habitat (to eliminate the possibility that birds followed vegetation cues rather than social cues). At the end of the breeding season in 2006, each site was given one of three treatments: left alone (a control group); song playbacks with male decoys (location cues); song playbacks with male decoys, plus female decoys attending fledgling decoys with with playbacks of begging calls (public information).

That summer, the researchers checked all three types of sites for the presence of black-throated blue warblers that might be looking for future breeding habitat. Sites with an artificial social cue were more likely to receive visits from fledgling warblers than the control sites. Both males and females were observed at the test sites.

The following year (2007), researchers conducted point counts at the test sites to check for warbler activity. Male warblers were far more likely to set up territories at sites where they had heard playback of territorial songs or fledgling calls the year before than at control sites. Females seemed to follow the presence of males; females were observed only at test sites where a male warbler was present.

Since warblers were equally likely to return to sites with location cues (song playback) and public information (song playback and dummy nests), the researchers surmised that late-season birdsong alone was a reliable indicator of good nesting habitat. To test this, researchers checked 60 known warbler territories for singing males.

Song frequency within territories was positively correlated with reproductive success, but only towards the end of the period observed.... By late in the breeding season (31 July), singing was 5.1 times (95% CI: 1.89-22.28) more likely on territories that successfully fledged young than those that did not. Conspecific song in the post-breeding season was therefore a reliable indicator of breeding success.

This result may be of interest to birders who volunteer for breeding atlases or other types of nest surveys.

Birdsong turns out to be a complex and powerful communication tool. For a short-lived species such as the black-throated blue warbler, which has to migrate thousands of miles between its wintering and breeding grounds, individual birds have relatively few chances to produce offspring. Reliance on a social cue like birdsong helps young birds avoid making some nesting mistakes in their first breeding season. They thus can produce more offspring over the course of their lives. It also holds advantages for the species as a whole, since local populations will be able to adapt more quickly to changes in their environment.

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Matthew G. Betts, Adam S. Hadley, Nicholas Rodenhouse, and Joseph J. Nocera, "Social information trumps vegetation structure in breeding-site selection by a migrant songbird." Proceedings of The Royal Society B (online edition, published June 17, 2008). doi:10.1098/rspb.2008.0217