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.