Review: The Warbler Guide

Warblers occupy a special place within the imaginations of North American birders. Warblers appear in a diverse array of colorful plumages, but they are not just eye candy. Their elusive habits and complex plumage makes finding and identifying them a satisfying challenge. Most birders have only a few weeks to see the vast majority of warblers in fall and spring, so there is little danger of their appeal wearing off, as sometimes happens with colorful resident species. Even after birding for ten years, I still have not mastered every plumage for every eastern warbler, and there are some species I still have not seen (like Kirtland's Warbler) or only seen once or twice (like Mourning and Connecticut Warblers).

Birders now have a new field guide to assist with finding and identifying warblers: The Warbler Guide by Tom Stephenson and Scott Whittle, published by Princeton University Press. The guide joins existing guides like A Field Guide to Warblers of North America by Jon Dunn and Kimball Garrett; Warblers of the Americas: An Identification Guide by Jon Curson, David Quinn, and David Beadle; and Stokes Field Guide to Warblers by Lillian Stokes.

A few features make The Warbler Guide distinctive. The most obvious at first glance is the sheer amount of visual information presented for each of the warbler species. (You can see a sample species account in this pdf.) For some species, the accounts are broken into drab birds vs. bright birds or fall vs. spring. To me, the accounts emphasize the best of the "field marks" vs. "whole bird" methods of identification. While it checks off diagnostic features (what might be called "field marks"), it goes beyond those to show how each bird appears from numerous angles. The photos also show characteristic behaviors and postures, which can be useful evidence in differentiating one species from another.

Another is that it uses a system of symbols and abbreviations with color coding to convey information about each bird. This may appeal some readers, but I prefer that a species account tell me the information in words rather than send me off to some key to find out what the symbol means. The guide also includes a quick finder that covers many angles and plumages. While useful, it starts on page 100, which makes referencing it less quick than it might be if it were placed near the beginning or end of the guide (as the quick finders are in the Crossley ID Guides). The publisher has helpfully provided PDFs of these quick finders on its website, for anyone to reference.

More important is the use of sonograms to represent warbler songs and calls. Sonograms were first introduced in printed field guides with Birds of North America: A Guide To Field Identification by Chandler Robbins, Bertel Bruun, Herbert Zim, and Arthur Singer, but they never caught on enough for authors and publishers of other birding field guides to feel the need to follow suit. Instead, it has been standard for field guide authors transcribe sounds into phonetic sounds, like kek-kek-kek-kek, or mnemonic phrases, like sweet-sweet-sweet-a-little-more-sweet. The trouble with the latter approach is that not everyone hears bird sounds the same way, and mnemonic phrases often do not the rhythm of the song they represent. Sonograms offer a more accurate way to represent bird sounds. However, sonograms take some skill and practice to interpret correctly. To that end, The Warbler Guide includes an extensive guide to sonograms and learning bird sounds in its introduction.

The Warbler Guide by Tom Stephenson and Scott Whittle is an innovative guide for learning and identifying North American wood warblers. It stands out from existing field guides, particularly in its inclusion of sonograms for every species. Any birder with an interest in warblers will want this guide as a stepping stone to more advanced identification skills.

New Program to Benefit Golden-winged Warblers

Illustration by Louis Agassiz Fuertes

The Golden-winged Warbler is one of the fastest-declining North American warblers. Its range has been shifting northward, whether due to climate change, competition (and interbreeding) from Blue-winged Warblers, habitat loss, or some combination of factors. A new federal program called Working Lands for Wildlife is intended to benefit Golden-winged Warblers and several other declining species. More specifically, the initiative will address the availability of adequate habitat in the warbler's breeding range.

Before widespread European settlement of the Appalachian region, Golden-winged Warblers relied on young forest or open woodlands created by natural fires, natural disasters, or beavers. During the early and mid-part of the Twentieth Century, much of the region was cleared through timber harvesting, and later, through strip mining for coal. Second growth vegetation and revegetation of these areas resulted in habitats that were conducive to species such as the Golden-winged Warbler. Over time, these areas have matured or become dominated by species that do not provide the habitat structure that warblers need.

The WLW initiative will focus on creating and maintaining the types of habitat necessary to sustain breeding populations of warblers in and around their current breeding areas. This will include efforts designed to expand the existing Appalachian range of the species and increase the amount of available habitat throughout the Appalachians. Two particular challenges are that many key areas are located within a matrix of lands with mixed ownership and there are potential conflicts with regard to commercial timber harvests.

The projects will presumably also benefit other animals that use the same habitat.

Kirtland's Warblers Like Young Forests

One of the early conservation challenges in rebuilding the Kirtland's Warbler population was providing sufficient nesting habitat. These birds nest in jack pines that are five to fifteen feet tall – in other words, very young forests. Jack pines need fire for their seeds to germinate, so stands of young jack pines are relatively uncommon in a context where forest fires are carefully controlled. Fortunately, conservationists found ways around this problem, and the Kirtland's Warbler population has recovered steadily since its nadir.

Kirtland's Warbler / Photo credit: Dave Currie

An interesting finding is that Kirtland's Warblers prefer young, disturbed forests on their wintering grounds as well as their breeding grounds.

But those extensive efforts only occurred at the Kirtland's summer home, so a team of researchers reviewed the conditions of many a warbler's winter home - the Bahamian island of Eleuthera. They did this by painstakingly putting together Landsat data to create cloud-free images of the isle's forest cover....

The researchers did this not just once, but ten times, obtaining a record that spans a 30-year time period. According to Helmer, this allows them to tell how long it had been since the forest was last disturbed by fire, crops or grazing.

What the scientists discovered was that, like in their summer homes, Kirtland's warblers are found in young forests. On Eleuthera, these forests only occur after a disturbance of some sort - like fire, clearing for agriculture, or grazing. And grazing turns out to be a disturbance the warbler can live with just fine. Old forest whose underbrush has been munched on by goats provides the most suitable habitat for warblers, said Helmer.

The results, published in this month's issue of Biotropica, suggest that goat grazing stunts the forest regrowth, so that the tree height doesn't exceed the height beyond which important fruit-bearing forage tree species are shaded out by taller woody species. Helmer said that understanding how and where the warbler's winter habitat occurs will help conservation efforts in the Bahamas.

Helmer said that a unique feature of warbler's winter habitat is that the age of this forest correlates very strongly with its height.

Taxonomic Revisions To Iconic Species: Wood Warblers and Fossil Birds

Yesterday the AOU published its 52nd Supplement to the AOU Checklist (pdf). Each year, the supplement contains additions, splits, lumps, and other revisions made by the AOU's checklist committee at its spring meeting. There are a number of significant changes in this year's supplement. One of them is a split in the moorhens: the Eurasian form retains the name Common Moorhen (Gallinula chloropus), while the American birds become Common Gallinule (Gallinula galeata).

Formerly Dendroica coronata, now Setophaga coronata / Photo by Frank Miles (USFWS)

The change likely to cause the most controversy is a full-scale revision of the wood warbler family (Parulidae). The move has been rumored for almost a year since the publication of a proposed reclassification of the family based on genetic analysis. I have avoided talking about the proposed changes since I do not have access to the original research informing the changes, but there are several summaries on the web. A good discussion of the reasoning behind the changes is at Biological Ramblings. There are some additional diagrams of the changes on David Sibley's blog. The short version is that genetic relationships do not match the traditional division of the wood warbler family into genera. The result is a reordering of the genera, with some being folded into others.

Here is the ordering of the wood warbler genera as they now stand:

• Seiurus: This genus has one species, Ovenbird, which is unlike most of the other warblers in its appearance and habits.
• Helmitheros: Another genus with one species, Worm-eating Warbler.
• Parkesia: The two waterthrush species, which were split from Seiurus last year.
• Vermivora: This genus lost several species to a split last year and now contains only the extinct Bachman's Warbler and the closely-related Blue-winged and Golden-winged Warblers.
• Mniotilta: One species, Black-and-white Warbler.
• Protonotaria: One species, Prothonotary Warbler.
• Limnothylpis: Yet another genus with only one species, this time Swainson's Warbler.
• Oreothlypis: This genus was created last year with most of the former Vermivora warblers and two members of the Parula genus.
• Leucopeza: One species, the possibly-extinct Semper's Warbler.
• Oporornis: Most of the former members of this genus were moved into the genus below; it now contains only the Connecticut Warbler, which has the unusual habit (for a warbler) of walking on the ground.
• Geothlypis: Traditionally this genus only the yellowthroats. Now it also contains the species exiled from Oporornis (like Mourning and Kentucky Warblers).
• Setophaga: While originally this was a small genus, containing only the American Redstart, it now contains all of genus Dendroica and two species of genus Parula, as well as the Hooded Warbler. Even though this is basically the old Dendroica genus, it is called Setophaga because that name has priority (i.e., it was published earlier in the historical record). The move results is an old situation where the family Parulidae no longer has a matching genus Parula, and the name Dendroica disappears from the checklist.
• Myiothlypis: One species in North America, Buff-rumped Warbler. There are more species in this genus, but most of them are in South America.
• Basileuterus: This is another Neotropical genus. This genus and Myiothlyis were traditionally considered a single genus.
• Cardellina: This genus contains the Red-faced Warbler, as well as two members from Wilsonia and two from Ergaticus. 
• Myioborus: These are the Neotropical redstarts and whitestarts. 
• Zeledonia: Wrenthrush, a Neotropical species.
• Icteria: One species, Yellow-breasted Chat, an oddball among warblers.
• Xenoligea: One species, White-winged Warbler.
• Microligea: One Neotropical species, Green-tailed Warbler.
• Teretistris: Two Neotropical species.

The last few genera, including the Yellow-breasted Chat, may not belong in Parulidae at all, but the AOU has held off reclassifying them, perhaps until there is better evidence about where they truly belong.

Over the past few months, several people have contacted me out of concern about the changes, especially the removal of the name Dendroica from the official taxonomy. I have been using the name "dendroica" as an internet handle since 2005, on this blog, on Twitter, and elsewhere, so I am sad to see that it will not longer match a warbler genus. At the same time, taxonomy is constantly subject to revision as new relationships are discovered, and the best available science today may be overturned tomorrow.

On the same day that the AOU published its checklist supplement revising the wood warbler family, another iconic species had its traditional placement questioned. A newly-discovered fossil species, named Xiaotingia, suggests that Archaeopteryx may not belong to the bird lineage, but to a parallel group, the deinonychosaurs. Ed Yong explains the consequences of such a change:

Meanwhile, others have noted that Archaeopteryx has many features that are only found among the deinonychosaurs. For example, they share a distinctive hip bone, and they both have a large hole above their noses (the “premaxillary fenestra”) that other birds and dinosaurs lack. Any many of the features that supposedly characterise Archaeopteryx and other birds, such as feathers, a wishbone and long powerful forearms, are also found in deinonychosaurs.

This is more than just a matter of shuffling cards. Archaeopteryx’s position has been so sacrosanct that its body had guided many of our ideas about the origins of birds. It grounds our understanding of this group. For example, it was previously thought that most primitive birds and their closest dinosaur relatives had lightly built skulls, which might have been useful for flight. “Instead, our study suggests that primitive birds had robust and rigid skulls,” says Xu.

“Our study also suggests that most primitive birds were herbivorous animals,” he says. “Previous studies which suggested that flight evolved in the [meat-eating] context (such as wings evolving for catching prey) need reconsideration.” Witmer writes, “Clearly, without the safety net of good old Archaeopteryx at the base of the birds, we’ve got some fresh work to do.”

But Gerald Mayr, who studies fossil birds at Germany’s Sneckenburg Museum, is unimpressed with the new discovery. “I fear that it is a bit hyped and that the conclusions are not as novel as the authors claim,” he says. Mayr is one of several palaeontologists who think that the deinonychosaurs are actually birds themselves. According to him, they’re flightless members of a group that includes Archaeopteryx and modern birds, like smaller extinct versions of today’s ostriches and emus.

See his blog for pictures of the new species, Xiaotingia, and diagrams of the new proposed taxonomy.

Whether or not the authors are correct in their placement of Archaeopteryx among the deinonychosaurs, it is clear that there were a lot of proto-birds and bird-like creatures and deciding which deserve to be called "birds" and which "dinosaurs" is not necessarily easy. There are relatively few fossils at that point in the lineage, so there is potential for one or two discoveries to disrupt the current alignment. Wherever Archaeopteryx belongs on the new taxonomic tree, I think it is still safe to see it as symbolic of the evolutionary relationship between birds and dinosaurs, even if it does not belong in the direct lineage of modern birds.

Changes in Rainfall Affect Birds' Wintering Grounds

Migratory bird species that breed in the U.S. and Canada often winter in the Caribbean, Central America, and South America. A Smithsonian study of American Redstarts on their wintering grounds in Jamaica found that rainfall changes disrupted the birds' migration schedule in the spring.

Precipitation in Jamaica is highly seasonal, with consistent rainfall from September to November and a pronounced dry season from January to March. The scientists observed the redstarts in their non-breeding territories for five years during the dry season. They paid special attention to the annual variation in dry season rainfall. The correlation between the amount of insects in a bird's territory and the timing of its departure suggested to the team that annual variation in food availability was an important determining factor in the timing of spring migration. Had the redstarts relied on internal cues alone to schedule their spring departure, they would have all left their winter territories at the same time each year.

"Our results support the idea that environmental conditions on tropical non-breeding areas can influence the departure time for spring migration," said Colin Studds, a postdoctoral fellow at the Smithsonian Conservation Biology Institute's Migratory Bird Center and lead author of the study. "We found that the same birds changed their spring departure from one year to the next in relation to the amount of rainfall and food in March."

During the past 16 years, the dry season in Jamaica has become both increasingly severe and unpredictable, leading to an 11 percent drop in total rainfall during the three-month annual drought. Making the future even more dire, climate models predict not only increased warming on temperate breeding areas but also continued drying in the Caribbean.

The result has obvious implications for climate change, since warmer average temperatures are likely to reduce rainfall in many areas. A major question is how birds will cope with the disrupted migration schedule. In many cases, birds time their migrations to arrive on their breeding grounds just as certain food sources are becoming available, whether those are insects or seeds or some other source.

Photos of the Tardy Northern Parula

As I mentioned in yesterday's post, I found a first-winter Northern Parula in my local park on Tuesday afternoon. Yesterday afternoon, I returned to the park and re-found the warbler foraging in more or less the same spot along the riverbank. This time I was able to take some photos to document the sighting better.

Northern Parulas are not regular winter residents in New Jersey. In fact, most of them are gone by mid-October, with only a few lingering into November. Like other warblers, Northern Parulas are primarily insectivorous, which makes it difficult for them to survive a cold winter at northerly latitudes. While they breed throughout eastern North America, they spend their winters in the Caribbean or Mexico and Central America. This warbler should be well south of here by now.

The greenish head and green-tinged flight feathers mark it as a first-winter bird, and the lack of any orange or red markings around the neck suggest that it is a female. (I am not sure whether that character is reliable for sexing first-year birds.) One detail I had not noticed initially but saw in the photos is the yellow wash on the flanks. Not all field guides show this marking.

I probably ended up with more photos of this part of the bird than any other.

A Lingering Blackpoll Warbler

Yesterday morning I was at Trenton Marsh. This is a good place to visit in fall and winter since the freshwater tidal marsh (the northernmost along the Delaware River) attracts migratory dabbling ducks and other interesting birds. Waterfowl are already starting to gather in the marsh. However, they do not seem to be at their peak numbers yet. I suspect that the relatively warm fall* allowed a lot of birds to stay further north. Water birds in the marsh included about 50 Gadwall, along with smaller numbers of American Wigeon, American Coots, Ring-necked Ducks, Green-winged Teal, and a lone Wood Duck.

The most surprising sighting was a first winter Blackpoll Warbler. It was foraging low in the shrubs along the main entrance trail (the one running from the parking lot between the impoundments) in the company of Yellow-rumped Warblers and Ruby-crowned Kinglets. I had some good looks at the warbler since it would sit or hop out in the open, but it would hop back behind branches whenever I had my camera in position to take a photo. Other songbirds included a Winter Wren and a half dozen Golden-crowned Kinglets.

Some of the trees still had their foliage, so the view across the marsh was colorful.

In some impoundments the water level appears to be maintained by a beaver dam. Several mounds in this section of the marsh appeared to be beaver lodges. This lodge was the largest of them.

Finally, this tree, which I think is a Red Maple, has an unusual shape. I am intrigued that the trunks grew apart from a common base but then rejoined a few feet further up the tree.

* Worldwide, this October was the warmest ever recorded; in the lower 48 United States it was the eleventh-warmest October.

In Search of the Golden-winged Warbler

Yesterday I took a train to Ramsey to meet Bev since she knows of a good spot for Golden-winged Warblers and generously offered to take me there. The place is just over the New York border and is as nondescript as a birding spot can be. Along the side of a road there is a small, unmarked pull-off, and beyond that is a powerline cut running alongside a stream. It is the sort of place one might pass by without even noticing its presence. The great thing is that Golden-winged Warblers breed there, so they are reliable from one year to the next.

Our morning began auspiciously with a repeated bee-buzz, the standard call of a Blue-winged Warbler, sounding from the trees. This was not actually a Blue-winged Warbler but a Brewster's Warbler, one of the hybrid forms of Blue-winged Warbler and Golden-winged Warbler. This bird had white undersides, a gray nape and back, white wingbars, a golden crown, and a black eyeline. The Brewster's was not shy and sang from prominent perches near the trail.

As we continued along the power cut, we saw many other birds. Northern and Louisiana Waterthrushes called from the wooded area on the left side of the trail. Baltimore Orioles were very prominent, singing and chasing each other in the treetops. Indigo Buntings were also darting back and forth across the trail. Close to the pull-off I saw a female American Redstart add material to a nest; several other warblers were also gathering nest material nearby. Blue-winged Warblers sounded from a few places but did not show themselves. Yellow Warblers sang all along the trail and were actively gathering nest material or chasing rivals.

Finally Bev heard a Golden-winged Warbler calling from a swampy area about half a mile down the trail. Unfortunately it was difficult to locate the sound over the racket put up by a Great-crested Flycatcher, but I heard it clearly enough to identify it. Just as we thought we had figured out where the Golden-winged Warbler was, a Broad-winged Hawk landed on a snag above the bushes. This silenced all of the birds (well, except for the flycatcher). Once the hawk went away, some activity resumed. A couple of Eastern Bluebirds appeared in the snags above the swamp; one appeared to be carrying an insect, presumably to feed to nestlings. A Wilson's Warbler landed just below eye level and paused briefly before disappearing. A few other warblers such as Chestnut-sided, Black-throated Green, and Magnolia were active in nearby trees.

After waiting a little longer by the swampy area, we decided to head back and bird the other side of the pull-off. The other side was more open with small beaver lake, making for a slightly different set of species. A lot of Red-winged Blackbirds were patrolling their territories; meanwhile a few Common Grackles were foraging, and a Brown-headed Cowbirds sang on top of a telephone pole. Several Tree Swallows darted back and forth over the lake. Eastern Kingbirds hawked insects from dead snags near the lake's edges. In addition to the usual waterfowl, there was a pair of Wood Ducks. The shrubs along the path had more Baltimore Orioles and Yellow Warblers. At one point I thought I heard a Golden-winged Warbler, but a flock of motorcycles roared past, and it did not call again. We still got one good bird, though. Bev saw, and I heard, a Kentucky Warbler low in the bushes near the edge of the lake.

Since I had gone up specifically for Golden-winged Warbler, we decided to try once more to see one. So we walked back down the trail past the pull-off to the swampy area. Once again Bev heard them singing. This time I saw one perched out in the open at the side of a large tree. It was cooperative and sang in the open for several minutes while a nearby rival answered. Once I was satisfied, we left and headed to Doodletown.

Doodletown is an abandoned village near Bear Mountain. It is more surprising that it was once inhabited than that it was abandoned because it is necessary to climb a steep hill to reach the former village's site. The reason for a birder to visit is that many warblers stop on the hill during migration and some stay to breed. Our best bird there was Cerulean Warbler, of which we may have heard a half dozen (only one of them seen). There were just as many orioles here as at the pull-off spot, including one Orchard Oriole near the trailhead. We also saw blackpoll and heard a singing first-year male American Redstart. We also got nice looks at a Blackpoll Warbler and a Blue-winged Warbler. A few other warblers, like Hooded Warbler and Magnolia Warbler, sang along the trail, but were difficult to find.

Once we had found what we could at Doodletown, we called it a day. We ended the day with 16 species of warblers and over 50 species overall. Both of the places we birded are great locations, and Bev is a great guide.

Warbler at a Hummingbird Feeder

This video of a warbler visiting a hummingbird feeder was posted on YouTube.

Songbirds sometimes visit hummingbird feeders, either to drink nectar or to catch insects attracted to the feeder. (See the photos here for another example.) Many warbler species, which primarily eat invertebrates during the breeding season, will drink nectar from flowers on their winter grounds in Central and South America. So it is not all that surprising that they would take advantage of artificial nectar sources as well.

The bird in the video above is most likely a Prothonotary Warbler. Not many warblers have that combination of bright yellow throat and breast, white vent, and plain upperparts (with a bluish cast). The dark head may indicate a hatch year bird. While spring adult males have bright yellow head, other plumages show varying amounts of olive on the nape and crown, with the most olive coverage on first fall birds. Prothonotary is one of the warbler species known to nectar.

The only element that bothers me is the apparent dusky neck,* but that could be an effect of the lighting, which appears to be coming from behind. I also do not see location information on the video or user pages, so there is a question of whether the range is appropriate. The site is in North Carolina, so this would be within the Prothonotary Warbler's normal range. What do you think?

* After checking a few more sources, I found that first fall Prothonotaries may have an olive wash on the flanks and throat.

Thanks to Peter Vankevich for bring the video to my attention.

Warblers in Boxes

When I think of southern swamps, there are a few bird species that come to mind – Pileated Woodpecker, Red-shouldered Hawk, Barred Owl, Northern Parula. But none is more closely associated in my mind with southern wetlands than the Prothonotary Warbler. The ringing songs of these bright yellow birds are a prominent feature of spring and summer mornings in wetlands from Maryland southward.

Prothonotary Warblers are one of only two North American wood warbler species to nest in cavities. (The other is Lucy's Warbler.) This imposes a natural restriction on nesting opportunities. Even where the habitat is right, the warblers must compete for nest sites not only against members of their own species but also against other cavity nesters like Tree Swallows and House Wrens, as well as introduced species like European Starlings. While it presents a challenge for nesting warblers, it also makes it possible for people to help the species directly by providing additional nesting boxes that meet their needs.

Volunteers in Virginia have been doing just that over the past few decades. Virginia is one of the few places where the Prothonotary Warbler's breeding population has been increasing, thanks to an active program of installing and maintaining nestboxes, coupled with the protection of appropriate habitat. There are currently about 500 artificial nest sites in eastern Virginia, and volunteers continue to add more.

This year, the attempt to add an additional 60 nest boxes to the Northwest River State Natural Area in Chesapeake ran into protests from a nearby landowner.

But Luton also made it clear he wanted no part of a scientific project next door at the Northwest River State Natural Area, where volunteers want to help revive populations of a small, yellow songbird - the prothonotary warbler - struggling against a tide of predators and vanishing habitat.

Speaking before the Virginia Marine Resources Commission, a state agency debating whether to allow construction of 60 bird boxes on the Chesapeake preserve, Luton said he feared the little bird might some day be declared an endangered species.

Citing its decline across most of the United States - except in Virginia, where numbers are increasing - Luton reasoned that the warblers could jump across Smith Creek and take up residence on his land, where federal endangered-species protections "could be a catastrophe."

"I'm fighting for my property," he told the commission.

Eventually the Virginia Marine Resources Commission decided to install 60 boxes on the preserve anyway, but not along the border of Luton's property. This course of action was probably the easiest way of continuing the important conservation program while minimizing conflict. However, the case raises some important questions. There are a lot of issues to unravel in this story, and I doubt that I will do any one of them justice in this short post. But here are a few problems that I see.

First, there is a certain incoherence in fearing that Prothonotary Warblers might be listed as a federally endangered species but obstructing actions that would prevent further decline. The best way to avoid any hardships that an endangered species listing might impose is to avoid having to list a species in the first place. In the case of the Prothonotary Warbler that means preserving southern wetland habitat and maintaining adequate nesting sites for a sustainable breeding population. One of the commissioners noted this when he issued the decision.

"I hear what you're saying, Mr. Luton," said commission Director Steve Bowman. "But it seems the more you have of them, the less likely they will be on the endangered list."

Second, I have to wonder just how likely the Prothonotary Warbler is to be listed, or at least to be listed any time soon. This species has experienced a substantial decline in recent decades, as much as 30-40% since 1966. This decline, while startling, is only enough to place the species with a yellow flag on the Audubon Watchlist and as a species of Least Concern on the IUCN Red List. There are many bird species that have suffered far worse declines over the same period.

As far as I can tell, Prothonotary Warbler is not currently a candidate for federal listing. This places it in line behind other candidates (such as the rufa subspecies of the Red Knot) that have suffered even more dramatic declines yet have languished on the candidate list for years without being given the full protections that come with listing under the Endangered Species Act. In part, this was a result of the Bush administration dragging its heels on species protections, but so far the Obama administration has not shown much interest in wildlife conservation, either. This makes me skeptical that the Prothonotary Warbler would suddenly be rushed through the system, especially since the organizations that might push their cause seem more concerned with species threatened by climate change right now.

In other words, Luton probably has little to fear in terms of the Prothonotary Warbler becoming an officially endangered species anytime soon. And even if it did, this would not necessarily mean restrictions on his property. Much would depend on whether they were breeding there, how much of his property was occupied, and other factors – all of which are hypothetical at the present time. In addition, one of the warbler's biggest problems is that its wintering range in Central America and the West Indies is under pressure because of the destruction of mangrove forests to make way for other uses. Any conservation strategy for these warblers needs to deal as much with that threat as with preservation of potential breeding grounds in the United States.

Third, there is the problem of the intrusion of private interests onto public property. Luton wanted to block a conservation program on state property on the basis of a hypothetical future presence of a hypothetically endangered species on his own private property. The species is not on his property now, and we cannot be certain that any future presence of the species there would be caused by the nestbox program. The implication in all this is that the concerns of private landowners should trump the legitimate management decisions made by public officials, even when the harm claimed by the landowner only involves some possible future land use, not current conditions. In my opinion this sets a bad precedent for future wildlife management on public land.

Fourth, even on private land, property rights are not absolute. Landowners are not free to develop their properties as they see fit. Instead they must comply with a variety of laws from zoning regulations to fire codes to noise and nuisance ordinances. If a property is needed for a project that benefits the public, it can be seized (with compensation) through eminent domain. Endangered species protections are simply one set of regulations among many and not inherently more onerous than restrictions on building height or requirements for off-street parking. Compliance with such regulations costs money and limits how a property might be used, yet they are subject to far less opposition and paranoia than endangered species (and other environmental) protections.

The good news is that the nestbox project will continue, at least for this year, despite Luton's opposition. It has been very successful; this year alone 108 nestlings were banded in the 38 boxes at Northwest River Park, near the preserve in question. The program's success makes me think that other states within the Prothonotary Warbler's range would do well to follow Virginia's example and implement nestbox programs if they have not done so already.

(Top photo by Birdfreak.com; second photo by Robert Mussey. Thanks to long-time reader Peter Doherty for alerting me to this article.)

Cerulean Warblers Return to the Same Winter Habitat

Since I adopted the Cerulean Warbler as my blog's mascot, I try to keep abreast of news regarding the species. The tiny warbler has been rapidly declining in recent years thanks partly to the loss of mature forest breeding habitat to mountaintop removal mining and other developments and partly to the loss of 64% of its winter habitat. While the decline has not been sufficient to get it listed under the Endangered Species Act, this warbler has been the focus of intense research on this continent and in its winter range in South America.

Through the Nature Conservancy's blog, I learned of an interesting finding from a research station in Colombia's Andes Mountains: some Cerulean Warblers return to the same wintering grounds year after year.

This research is so exciting that every time I read the reports, I immediately want to head to the field to help out. Gabriel and his team have, since 2003, captured 49 individual Cerulean Warblers. They have used an innovative technique with aerial mist nets suspended on bamboo poles high in the canopy, which is what you have to do to capture this species. Most incredible, the team has recaptured 4 of these birds in different wintering seasons.

This has demonstrated, I believe for the first time, that some individual Cerulean Warblers return to the same wintering area in succeeding years — something we’ve always suspected, but have never proven. So you can meet some of the characters, on the left is a photo of a female Cerulean named Aleja, who was caught and banded in March, 2009. You can see some of the color bands that were placed on her, so she could be followed to study her behavior and diet.

The implications of this finding for conservation will be up to the researchers in the field to determine. However, I would like to suggest a few areas where it might be relevant. First, if individual birds return reliably to the same winter locations, it makes preserving the habitat at those locations all the more important. This is something where U.S. nonprofits can be of some assistance. Second, maintaining (and possibly expanding) these wintering areas will be easier if there is some incentive to keep them forested. One way to do that is through encouraging shade coffee production, which benefits Cerulean Warblers and other species. U.S. consumers (especially birders) can play a role here by providing a market for it. Finally, if warblers return consistently to the same breeding grounds and the same wintering grounds, chances are that they do the same for at least some migration stops. In that light, keeping migrationg stop-overs – even small ones – intact ought to be a major benefit.

(Photos: Top photo by Flickr user Petroglyph; second photo included in the linked blog post.)

Yellow-breasted Chat Video

I found this gem via the Smithsonian Migratory Bird Center's Twitter stream.

Evolution of the Wood Warblers

Ever since I started birding, I have especially delighted in the birds of the family Parulidae, the North American wood warblers. So it should not be surprising that this blog has one of its genera as its domain namesake, or that I write about them frequently, or that I use one species as my mascot. It is with good reason: these jewels of North American woodlands provide a prime example of avian diversity. The genus Dendroica, in particular, includes (at least) twenty-seven species with a multitude of plumages and specialized adaptations.

This remarkable diversity evolved in a short burst soon after the genus Dendroica split from its ancestral lineage. Most species in the genus emerged within its first million years, and then the rate of diversification slowed down considerably. One explanation for this is that rapid diversification occurs when new ecological opportunities open. As the available niches fill, increased competition from existing species makes it harder for new species to appear.

The authors of the linked paper devised a mathematical model to test that explanation against other possible causes for a decline in speciation rates. An extensive DNA analysis for all continental members of the genus established both the order in which new species appeared and how quickly they did so. (See their new phylogenetic tree below.) The timeline established via DNA analysis supported the idea that the diversification rate for Dendroica warblers spiked quickly and then dropped due to niches being filled.

Figure 1: Maximum clade credibility (MCC) tree from Bayesian analysis of all continental North American Dendroica wood warbler species. Nodes marked with asterisks are supported by posterior probabilities of more than 0.95. Tree is based on more than 9kb of mtDNA and nuclear intron sequence. Branch lengths are proportional to absolute time. (Source: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2008.0630)


This paper builds on an earlier finding that the Dendroica lineage arose in the late Miocene or early Pliocene, roughly five million years ago. That transition was accompanied by climate change. As the North American climate became hotter and drier, extensive woodlands fragmented into smaller patches. This change in the landscape may have given wood warblers their opportunity to diversify. Later in the Pliocene, the climate and landscape became more like the present, and those changes may have sparked the secondary burst of speciation.

As an aside, it is interesting that the oldest species in Dendroica – Kirtland's warbler (D. kirtlandii) – is also one of the most endangered species in the genus. (It is probably just a coincidence, since the genus's other endangered species – golden-cheeked warbler (D. chrysoparia) – is among the newest.) Modern humans, by contrast, appeared relatively recently and first entered North America even more recently. Millions of years before humans ever set foot on this continent, these tiny birds were winging their way between their summer and winter territories. That is an amazing thought to keep in mind when fall migration comes again.

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Source: Daniel L. Rabosky and Irby J. Lovette, "Density-dependent diversification in North American wood warblers," Proceedings of the Royal Society B, published online (July 8, 2008). doi: 10.1098/rspb.2008.0630

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

Kirtland's Warbler Discovered Nesting in Wisconsin

Three nests of endangered Kirtland's warblers have been discovered in Wisconsin.

The bird, one of the rarest members of the wood warbler family, typically makes its home in the northern part of lower Michigan, nesting in stands of young jack pines.

Officials say this marks the first time nests have been found outside Michigan since the 1940s, when nests were discovered in Ontario.

Females have been observed near the nests, which confirms the birds as a breeding species in the state, the Fish and Wildlife Service said.

Matteson said surveys were done as far back as 30 years ago until the 1980s and males were found in western and northwestern Wisconsin. But Matteson said there had not been any documented females until this year.

Kirtland's warblers have been the subject of intensive recovery efforts in northern Michigan. The warbler has very specialized requirements for its breeding habitat. It typically nests in relatively jack pine forests when the trees are about 16 to 20 feet tall. Forest fire suppression limits the young trees available for the warblers, so the state has been planting jack pine seedlings to maintain a steady supply. As a result of conservation efforts, the population has grown from a low of 201 singing males in 1971 to 1,486 in 2006.

I am glad to have some encouraging news to go along with the bad.

Taking a Bath

A black-and-white warbler stops to bathe.

And another black-and-white warbler forages at its winter home in Belize.

Coming Attractions

Coming soon, to a woodland near you:



Also, by the same user, here is a video from a spot I visited recently, Manasquan Reservoir in New Jersey:



The last shot is a bald eagle nest where an eaglet recently hatched.

Pine Warblers in December

On Sunday, December 3, I located a pine warbler in the state trees grove of the National Arboretum. (My post on the sighting is here.) This past Sunday, another birder relocated the bird in the same location.

Pine warblers are exceptional here in December. Over the past thirty years, only ten pine warblers have been recorded on the Washington CBC. The high count was three on last year's count.

Source: CBC Historical Results

Will it stick around for this Saturday's count?

No Listing for Cerulean Warbler

The US Fish and Wildlife Service has declined to list the cerulean warbler under the Endangered Species Act. Conservation groups had asked the government to list cerulean warblers in 2000; the FWS began a status review in 2002. The decision announced this week was based on a review of data and petitions submitted as part of a public comment period.

Although there is no precise estimate of the current abundance of the cerulean warbler, the Service used a 1995 population estimate of 560,000 warblers during its review of the species’ status. Based on 40 years of data obtained through the Breeding Bird Survey which indicates the population is declining at about 3 percent each year, the estimated population in 2006 would be approximately 400,000. At this rate of decline, the Service estimates the cerulean warbler population would number in the tens of thousands 100 years from now.

The FWS does plan to maintain some involvement in conservation efforts, as is noted in the press release linked above. The decision not to list removes some of the legal muscle that would assist conservation efforts. I can understand the decision to focus on species in greater trouble, but I have to wonder whether assuming a steady rate of decline is valid. The response by the Southern Environment Law Center notes that recent estimates of rate of decline have indicated an increase to a 6% decline each year.

The Fish and Wildlife Service failed repeatedly to meet federally mandated deadlines under the Endangered Species Act for responding to the petition. In the intervening years, scientists believe the bird's annual rate of decline increased from 4% to 6%, and threats to its habitat have worsened. ...

The Cerulean population has dropped almost 82% throughout its U.S. range over the last 40 years, making it the fastest declining warbler in the country. ... Once common, it has grown increasingly rare as forest habitat in both hemispheres has been destroyed and fragmented by logging, surface mining and development. In the U.S., the worst of the Cerulean's decline has been in the core of its range - 80% in the Cumberland Plateau in Tennessee, Kentucky and West Virginia, and 65% in the Ohio Hills in Ohio, West Virginia and Pennsylvania.

I have some comments about cerulean warblers in an older post.

Tags:

• Cerulean Warbler
• Conservation

Looking for Nuthatches, Finding Warblers

Late this morning I returned to the Arboretum for a walk and some birdwatching. I picked the meadows around the Capitol columns and the state tree grove as my area of focus, to see if I could find anything unusual there. As I passed along the south side of the meadow, I heard a nuthatch yanking in a nearby stand of pine trees. I went over to see what species was calling; it turned out to be a white-breasted nuthatch. As I was about to move on, a small yellow bird darted into view. I ran through the field marks quickly - yellow eye-ring, olive back, yellow breast with olive streaking - it was a pine warbler! I watched it for a while before losing it in another stand of pines a few yards away. The same tree where I spotted the nuthatch and pine warbler also held a male red-winged blackbird, in full regalia.

In the meadows I turned up lots of sparrows - few fields, a few songs, a few white-throats, and large flocks of juncos. A small flock of eastern bluebirds flew past the columns. I also spotted two eastern phoebes in the same meadows. Elsewhere, there was a red-shouldered hawk in Fern Valley and a pair of hooded mergansers in the large pond. There were also some large sparrow flocks in the boxwood area along Bladensburg Road. They were mostly the same species as before, plus a few towhees.

SPECIES SEEN: 31

Hooded Merganser
Red-shouldered Hawk
Ring-billed Gull
Rock Pigeon
Mourning Dove
Red-bellied Woodpecker
Yellow-bellied Sapsucker
Downy Woodpecker
Northern Flicker
Eastern Phoebe
Ruby-crowned Kinglet
Carolina Wren
Northern Mockingbird
Eastern Bluebird
American Robin
Carolina Chickadee
Tufted Titmouse
White-breasted Nuthatch
Blue Jay
American Crow
Fish Crow
European Starling
American Goldfinch
Pine Warbler
Eastern Towhee
Field Sparrow
Song Sparrow
White-throated Sparrow
Dark-eyed Junco
Northern Cardinal
Red-winged Blackbird

Tags:

• National Arboretum
• Birding