Warbler Guy, which wood-warbler clutch has the largest number of eggs?

Good question, Parker in New York City.

The answer is the Cape May Warbler (see female in photo, above), which usually lays six or seven eggs. Most other wood-warbler species typically lay four or five eggs in most instances. In extraordinary cases (that are seldom to rare), the Cape May deposits as many as nine eggs. In equally rare situations, merely four are laid.

Why does the Cape May lay eggs than other wood-warbler species? The answer may relate to the “boom and bust” cycle of its dominant food resource: spruce budworms (a larval form of a moth). When large population outbreaks of the spruce budworm occur, it behooves the Cape May to lay more eggs. Conversely, it makes sense that this species lays fewer eggs in years when spruce budworms are less plentiful.

Of course, this kind of phenomenon is not unique to Cape May Warbler. Many other bird species, in addition to other animals, act similarly in response to the presence or absence of food resources.

For more details about clutch sizes of North American breeding wood-warbler, see The Birder’s Handbook (Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye)

Other life cycle information about USA-breeding wood-warbler species appears in a “Warbler Tips ID Chart” at my Web site: www.warblerwatch.com (After arriving at this site’s home page, click on the button title “Warbler Tips ID Chart.”

Warbler Guy, which vagrant warblers have recently been seen in Alaska?

Good question, Thomas (in Cincinnati, OH).

According to the May, 2010 issue of Birding Magazine, the Willow Warbler (ABOVE PHOTO) (Gambell, St. Lawrence Island, 8/25/02), Sedge Warbler (9/3/07) and Pallas’s Leaf Warbler (9/25/06) are the three most recent significant observations.

(By the way, a vagrant bird is one that appears far outside its normal range. Some people believe “accidental” equates with vagrancy. Among a number of factors that cause a bird to become vagrant, genetics and weather conditions are two.)

Which warblers are predicted as upcoming potential vagrants to Alaska?

Candidates include Gray’s Warbler, Oriental Reed-Warbler, Black-browed Warbler, Pale-legged Leaf Warbler, Radde’s Warbler, and Japanese Bush-Warbler.

Warbler Guy, what are some good warbler identification resources?

Andy (in Lacrosse, WI), I suggest you see:

http://www.giffbeaton.com/warblers.htm

http://birding.about.com/od/identifyingbirds/a/warbleridentification.htm

http://www.enature.com

http://www.warblerwatch.com/warblertips.htm

Warbler Guy, do migrating male wood-warblers arrive earlier than females to nesting grounds?

(Above, a first-year male American Redstart is indicated by the slightly burnt-orange/amber outer tail feathers and forward flanks.)

Yes, Edward (in Cincinnati), multiple studies indicate males arrive earlier than females. One study (at Prince Edward Point, Ontario) even showed that the oldest adult American Redstarts arrived significantly earlier than second-year males of the same species. A similar trend was noted for approximately 20 other wood-warbler species.

Interestingly, species that spend the winter farthest north, arrive the earliest upon nesting grounds. That makes sense in the case of Yellow-Throated Warbler that arrive early in the spring in the Mid-Atlantic because they merely need to travel from as closeby as the southeastern USA where they spend the non-breeding season. This phenomenon supports the theory that males arrive early to take advantage of food resources and/or when climatic conditions are suitable, whereas females of the same species arrive when conditions are more ideal for successful nesting.

Later arriving species on their nesting grounds, including Blackpoll, travel from as far away as northern South America where they spend the non-breeding season. For this reason, during some spring seasons, it may not arrive on northern nesting grounds until June 1st and beyond.

Other wood-warbler species — Yellow-rumped and Pine Warbler, for example — that can subsist on berries and seeds, in addition to insects, are usually the earliest to arrive on nesting grounds. Among other early arriving species in the warbler march north include Palm, Black-and-white, Nashville, Wilson’s, Louisiana Waterthrush, Prothonotary, Northern Waterthrush, Wilson’s, and Yellow.

Warbler Guy, do all our returning eastern wood-warblers fly over the Gulf of Mexico during spring migration?

(Nashville Warbler, above. Note it’s often difficult to see its light brown-orange cap, though its prominent eye-ring and absence of wingbars are good field marks.)

“No,”(Byron in Laramie, WY) is the quick answer.

Although the majority of East Coast and Midwest breeding wood-warblers fly over the Gulf upon returning to the USA, there’s at least three that fly around the Gulf:
Nashville, Mourning, and Canada.

That is to say, these three “Circum-Gulf” migrating species use an overland route by arriving in the USA via Mexico.

The non-breeding season range of the Nashville Warbler is primarily in Mexico, so they have the least amount of miles to travel as migrators. Moving north in spring, they typically always arrive earlier than Mourning and Canada in northern Midwest and Eastern latitudes. In fact, among the 30 or so wood-warblers that birders observe annually in northern latitudes, Nashville may be considered an early arrival among the vanguard. Some of the Mexican wintering Nashville travel to the West Coast for breeding and are considered a different subspecies.

Canada and Mourning, on the other hand, are known as later arrivals in the warbler migration parade. Canada comes all the way from southern Central American and northern South America, so it makes sense that its route through Mexico takes longer than many other warbler species.

Patient birders often have to wait even longer into May to see Mourning. That’s because it winters almost exclusively in northern South America. Winging north requires Mourning to travel more miles than most arriving Nashville and Canada populations. As a result, Mourning usually doesn’t appear in its breeding territory until mid-May, often later in some spring seasons.

If, for example, cold weather occurs throughout much of May and northerly breezes prevail, then Mourning may not arrive until late May in portions of its northern nesting areas. Only Blackpoll is known to arrive later during these inclement seasons when many other warbler species may also arrive later than usual.

Warbler Guy, what are the answers to the most recent quizzes on your blog’s right column? (Jeremy K., Seattle, WA)

Here’s the answers, Jeremy, with corresponding date (if applicable) for each quiz provided as you scroll down from today’s date and backward in time:

1. March 2 Photo Quiz:

Photos from top to bottom = MacGillivray's, Connecticutt, Chestnut-Sided, Lucy's, Hermit

2. Which wood-warbler is typically the earliest long-traveling migrant back on the East Coast? West Coast?

Answer: Louisiana (remember, it said “long-traveling” migrant); Orange-crowned

3. March 1, 2010 article and corresponding quiz:

Which wood-warbler species has gained the most population by percentage in the last 20 years?

Answer: Kirtland’s, as the population increased to nearly 1,400 singing males by the mid-2000s after hovering around 200 males through the mid-80s.

4. January 10 Photo Quiz:

Photos from top to bottom = Aud.'s) Yellow-Rumped, Wilson's, Bl.-Thr. Blue, Blackpoll, Hermit

5. Approximately how many miles are trans-oceanic migrating Blackpoll (Warbler) traveling if they begin in New England and arrive in northern S. America (For help, see the 9/29/09 article)?

Answer: 2,150 one-way (for example, Blackpolls leaving New England travel as far as this distance to northern South America where they spend the non-breeding season.

6. Pretend you're attending an upcoming Christmas Bird Count (CBC) in any of the lower 48 states. Which two wood-warbler species are the most likely ones MOST people would see?

Answer: In most cases and during most years, it’s Yellow-Rumped and Common Yellowthroat (though Palm can sometimes persist and/or over-winter in some northern latitudes).

7. Can you name two wood-warbler species that are breeding endemics to one USA state?

Answer: Golden-cheeked (a true endemic that breeds only in Texas) and Tropical Parula, though the later breeds farther south outside Texas.

Warbler Guy, which warblers look alike? Which are the most confusing warblers to identify from each other?

Thanks, Gilman (in Paso Verde, CA)

Right, which photo is the Orange-crowned? Tennessee?


Warbler identification challenges are ALWAYS the leading questions I get in the spring.

So here's ten typical “double-take” ID challenges you’re likely to encounter when the going gets tough on the boardwalk as the warbler march begins:

(i.e., Knowing the breeding ranges and which habitats the following species tend to frequent and/or nest within is always helpful in identifying look-alikes from each other – among other factors.)

1. Chestnut Sided and Golden-Winged

2. Magnolia and immature Prairie

3. Black-throated Green and Townsend’s/Hermit hybrids

4. Yellow-throated and Grace’s

5. Kirtland’s and Palm (and Prairie)

6. Yellow-Rumped (Audubon’s subspecies vs. Myrtle subspecies) (and intergrades of Audubon’s and Myrtle occur in portions of British Columbia and Alberta)

7. Tennessee and Orange-Crowned

8. Ovenbird and Northern Waterthrush (or Louisiana Waterthrush (they are all in the same genus)

9. Connecticutt and Mourning

10. Mourning and MacGillivray’s