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I should have started this project earlier in the year. Spring is the time of year when nearly every birding trip, even if it is not as successful as we might like, brings a few new first-of-season (FOS) sightings. But migrants don’t just arrive haphazardly; there is an order to their appearance, with some species such as Pine Warbler and Yellow-throated Warbler arriving early, and species such as Bay-breasted Warbler arriving very late in the season.  So this spring I decided to keep track of the new birds that I see for the year and their first appearance date, in an attempt to document the early vs late arrivals. This is not meant to be a comprehensive schedule of arrival dates in the area because it is partly dependent on luck, and also on how often I go out birding and in what habitat, but this list should be useful in the future to anticipate new arrivals. Does everybody keep this kind of personal list? Have you considered doing it for your own sightings?

March 29 Black-headed Gull
March 29 Palm Warbler
April 5 Yellow-throated Warbler
April 5 White-eyed Vireo
April 9 American Bittern
April 9 Black-crowned Night-heron
April 9 Tricolored Heron
April 9 Wilson’s Snipe
April 9 Eastern Meadowlark
April 19 Whimbrel (lots..119!)
April 19 Willet
April 19 Little Blue Heron
April 20 Common Raven
April 21 Red-breasted Nuthatch (it has been a very tough winter to see them)
April 21 Blue-headed Vireo
April 21 Broad-winged Hawk
April 21 Louisiana Waterthrush (heard only)
April 21 Hooded Warbler
April 21 Wilson’s Phalarope (bird of the year so far for me)
April 23 Prothonotary Warbler
April 23 Wood Thrush
April 23 Blue Grosbeak
April 23 Merlin
April 25 Great Crested Flycatcher
April 26 Northern Parula
April 26 Prairie Warbler
April 27 Chimney Swift (I should have seen this species before today)
April 28 House Wren
April 30 Black Skimmer
April 30 Spotted Sandpiper
April 30 Least Sandpiper
May 1 Orchard Oriole
May 1 Ruby-throated Hummingbird
May 2 Baltimore Oriole
May 2 Warbling Vireo
May 2 Black-throated Blue Warbler
May 2 Blue-winged Warbler
May 2 Indigo Bunting
May 3 Green Heron
May 3 Yellow-breasted Chat
May 3 Semi-palmated Sandpiper
May 3 Yellow Warbler
May 3 Marsh Wren
May 3 Gull-billed Tern
May 4 Chestnut-sided Warbler
May 5 Whipporwill
May 5 Northern Waterthrush
May 5 Red-eyed Vireo
May 5 Acadian Flycatcher
May 5 Veery
May 5 Worm-eating Warbler
May 6 Blackburnian Warbler
May 6 Black-throated Green Warbler
May 6 Scarlet Tanager
May 6 Bay-breasted Warbler
May 6 Blackpoll Warbler
May 7 Red-headed Woodpecker
May 7 Solitary Sandpiper
May 7 Northern Rough-winged Swallow
May 7 American Redstart
May 9 Eastern Wood-pewee
May 9 Yellow-billed Cuckoo
May 10 Kentucky Warbler
May 10 Semi-palmated Plover
May 10 Pectoral Sandpiper
May 10 White-faced Ibis
May 10 Clapper Rail
May 11 Least Flycatcher
May 12 Nashville Warbler
May 12 Wilson’s Warbler
May 12 Swainson’s Thrush
May 12 Magnolia Warbler
May 12 Ruddy Turnstone
May 14 Black-capped Chickadee
May 14 Tennessee Warbler
May 14 Cape May Warbler
May 14 Canada Warbler
May 17 Barred Owl
May 17 Bank Swallow
May 17 White-rumped Sandpiper
May 17 Stilt Sandpiper
May 21 Common Nighthawk
May 22 Common Merganser
May 22 Yellow-throated Vireo
May 22 Common Gallinule
May 23 Alder Flycatcher
May 23 Willow Flycatcher
May 24 Black-billed Cuckoo
May 24 Golden-winged Warbler
May 26 Eastern Meadowlark
May 26 Horned Lark
May 26 Upland Sandpiper
May 26 American Kestrel
May 28 Least Tern
May 28 Common Tern
May 31 Cattle Egret
June 6 Red Knot
June 6 Piping Plover
June 13 Upland Sandpiper
June 13 Common Nighthawk
June 13 Grasshopper Sparrow
June 13 Horned Lark
June 20 Wilson’s Storm-petrel
June 25 Roseate Tern
June 25 Royal Tern
June 25 Brown Pelican
July 7 Summer Tanager
July 19 Yellow-crowned Night-heron
July 19 Black Tern
July 26 Western Sandpiper
July 26 Least Bittern
July 26 Roseate Spoonbill
July 26 American Avocet

Afterward: It seems like the idea worked out quite well. For example, with the vireos, White-eyed appeared first, then Blue-headed, then Warbling, followed by Red-eyed, and finally Yellow-throated. That is an expected order. For the flycatchers, we first see Eastern Phoebe (which arrived before I started this list), then Great Crested Flycatcher, then Acadian, Eastern Wood-pewee, then Least, Alder, and Willow Flycatchers.  Olive-sided and Yellow-bellied Flycatchers would be expected at the tail end of the season, but I didn’t see any this year. Analogous expected patterns of arrivals are seen for shorebirds and the warblers.  I’ll be doing this again next year to see how similar the patterns are to the 2018 arrivals.  Give it a try yourself next spring.

In a previous post I described patterns of early spring short-distance migrant sightings here in the New Jersey area. Since then I have continued to explore the eBird sightings data, and after looking at the maps, I am envious of those living in the northwest part of the state, who appear to be on a direct migration path for many species that are seen far less frequently here in the Pinelands, along the coast, or even in Cape May (the home of “So. Many. Birds.”).

Why am I envious? Let’s explain by starting with the pattern expected of birds that essentially migrate uniformly northward, not being affected by larger bodies of water like the Chesapeake or Delaware Bays. This group is typified by Scarlet Tanager, Great Crested Flycatcher, Eastern Kingbird, Yellow-breasted Chat, and Northern Parula that can be found throughout the state. That’s reassuring to see, but it’s also expected, so nothing too unusual there.

Scarlet Tanager sightings as of May 1, distributed fairly evenly across NJ and DelMarVa.

Eastern Kingbird sightings as of May 1. Like Scarlet Tanager, it is found all over NJ and DelMarVa.

Great Crested Flycatcher is also abundant all over our area and is evenly distributed.

Yellow-breasted Chat is just starting to appear in the area, but seems to be evenly distributed as of May 4.

As of April 28, Northern Parula was being seen along the immediate coast and also inland, with perhaps a slight preference to inland locations.

The more interesting thing is that not all species show this pattern. In fact, it will be interesting to see whether this pattern is the exception or the rule. For example, take a look at recent sightings of Warbling Vireo. Here we have a species that is barely being seen along the east coast south of Virginia, but instead is presumably migrating up the central flyway through Texas and the midwest, and then spreading northeastward. There are few sightings in south Jersey including Cape May, while it is being seen routinely north and even northeast of us, up into Massachusetts. This is clearly different from what we saw with that first group of birds described above.

Warbling Vireo sightings as of May 4, showing the absence of sightings along the south Atlantic coast.

A similar pattern is seen for other species that presumably migrate primarily through the central flyway. Look at Nashville Warbler, Blackburnian Warbler, Bay-breasted Warbler, and Mourning Warbler. After looking at these maps it’s now no surprise to me that it is difficult to find them in our area.

Nashville Warbler sightings as of May 4. Like Warbling Vireo, there are very few of them on the east coast south of Virginia.

Blackburnian Warbler appears to be a trans-gulf migrant, but then with fewer sightings along the eastern coast.

Zooming into the NJ area, we can see how Blackburnians mostly skirt around the DelMarVa peninsula and southern NJ.

Bay-breasted Warbler sightings as of May 4. This pattern seems very similar to Blackburnian Warbler, with sightings along the entire gulf cost, few sightings along the southeastern US, and then skirting the western side of New Jersey before progressing further northeast. There are no sightings in DelMarVa or southern NJ as of this timepoint, despite being seen as far north as Massachusetts.

Here’s the pattern for Mourning Warbler as of May 19. This is a great example of a bird that migrates completely up through Texas (not at all through the gulf and Florida, eventually spreading northeastward towards NJ.

This pattern is not restricted to warblers, as a similar pattern is seen for Swainson’s Thrush.

Here we can see Swainson’s Thrush migrating up the western side of New Jersey through a corridor that extends from Baltimore though NYC.

Could it be that these sighting maps are distorted due to the number of birders in the Baltimore, Philadelphia, and New York City areas, essentially creating an ‘artificial’ corridor that represents more birders rather than more birds?  I think that is not the case, based on what we see for Canada Warbler sightings.  Here are the sightings in the northeast, and I can easily imagine possible clusters near those three metropolitan areas.

Here is the distribution of Canada Warbler sightings surrounding New Jersey, showing that the birds most often are seen west of DelMarVa and southern NJ, in a corridor extending between Baltimore and NYC.

But if we zoom out on the map, that same corridor extends southward though the Appalachians, into lesser populated areas, so it is not entirely due to a greater number of birders, at least for this species.

And now zooming out we see that the the distribution of Canada Warbler sightings in the northeast does reveal a kind of corridor extending through the Appalachians.

As I said previously, it remains to be seen which of these patterns is more common, and whether the use of the central flyway is sufficient to explain the rarer migrants in southern NJ. But the interesting take-home message for me is that naïvely, I would think that the better place to find northward-moving migrants in NJ during spring would be to head southward to Cape May, but instead the best overall locations appear to be in the northern part of the state. This conclusion is borne out by great spring days that I’ve had over the years at Garret Mountain, but I used to think that was a special migrant trap situation. Now I lean towards it being just one nice place for birds to rest within suburban sprawl on a migratory corridor.

I leave you with one more pattern, that of Blackpoll Warbler. I know that Blackpolls have an interesting southward fall migration, heading out to sea from the northeastern US on their way to the Caribbean, but their northward spring migration has an interesting pattern too, with sightings not just in TX and the gulf coast states, but including abundant sightings throughout Florida, up through Georgia, then bifurcating into east coast and central branches.  I’ll have to read more about this species as I continue to follow spring migration through eBird.
I realize that this post might not be of immediate interest to those of you who live outside of my home area of New Jersey, but I hope that it encourages you to use eBird sightings as a way to envision migration patterns in your area. On the eBird site use the “Explore” option and then “Species Maps” to search for sightings of any species of interest, setting a narrow search window of one month, zoom in to your home region, then try it again the next month, and see if any interesting patterns emerge. I have suggested to the folks at Cornell that they enable narrower or more specific searches, but I have not heard back from them yet.

Along with most other birders this time of year, I am eagerly anticipating spring migration. Last year (and the prior year too if my memory serves me well) the numbers of migrants that I saw were disappointing, but I don’t know if it was because bird numbers were low all over, or if I was in the wrong locations, or if they were migrating further inland due to wind patterns. Or perhaps southern New Jersey is just not in an optimal geographical location for spring migration. For that reason, I have been watching the sightings of our early season migrants to see if there are any interesting patterns, and I’ll share my initial findings with you here.

By looking at recent eBird sightings, I have noticed at least four different patterns, each of which is shared by two or more species. Before going any further, however, it is probably worth admitting that eBird sightings are an imperfect measure of bird distributions, but it is a pretty good indicator of the likelihood of seeing a particular species, which is what most birders are interested in. So let’s start with the simplest pattern, in which a species appears essentially uniformly across the state. For a species such as Wilson’s Snipe, it essentially doesn’t matter where you are located in NJ; snipe apparently are nearby in suitable habitat early in the season. It’s not clear to me how many of the sightings in the map below are due to migration, as Wilson’s Snipe can overwinter in our area. The number of blue markers (which indicate sightings from this year that are more than a month old) is indicative of this hardy species. At the level that I am able to access the data, it is likely that other half-hardy species in which part of the population remains in NJ over the winter would show a similar pattern.

Here is the eBird sightings map for Wilson’s Snipe from April 2, with the sightings distributed relatively evenly throughout the area shown here, even beyond New Jersey.

Other species, however, exhibit a different pattern, where the northward migration is obvious, and where they appear to migrate principally along the western edge of NJ, thereby bypassing the Jersey coast (and possibly the DelMarVa peninsula too). Look at the sightings for Palm Warbler and Northern Rough-winged Swallow from early April.

The sighting map for Palm Warbler from April 3.

This is the eBird sighting map for Northern Rough-winged Swallow from April 7. Notice the similar pattern as Palm Warbler, with a relative paucity of sightings across the DelMarVa peninsula and southern NJ.

Notice how the sightings are more numerous along the western shore of Chesapeake Bay, continuing up the Delaware River valley and across northern NJ, bypassing much of the DelMarVa peninsula and southern NJ.  This is an interesting class for me, especially if it is shared by many other species.  We need to realize that these sightings are just the forefront of the migrants for these species, and because they are fairly abundant birds, as the season progresses we will have little problem seeing these species even along the Jersey coast.  But to me this indicates that a local migration corridor might exist and if this pattern holds for less abundant species, then western NJ would provide the best opportunity to view them. So what drives this kind of pattern?  I don’t know yet.  It could be that these are species that prefer not to migrate over water, so they are trying to avoid crossing the Chesapeake and Delaware Bays.  Perhaps their ultimate breeding grounds are further inland, so they are avoiding the eastern coast. Perhaps the coastal region is lacking food sources or habitat that favor their survival during migration. I really don’t know, but I will be interested in seeing how many other species migrate this way. As you can see below, this pattern seems to be shared with House Wren too.

House Wren sightings from April 22.

A third pattern is exhibited by Common Yellowthroat and Black-and-white Warbler. In contrast with the previous three species, Common Yellowthroat and Black-and-white Warbler seem to favor the coast, being sighting readily in DelMarVa and southern NJ, with a line of migration moving steadily and evenly northward. Does this pattern occur because there is plenty of breeding habitat for these species in southern NJ and in the pinelands, or can there be other reasons?  Are they more comfortable migrating over larger bodies of water? Knowing how many other species exhibit this pattern might help to figure it out.

eBird sighting of Common Yellowthroat from April 18.

Sightings of Black-and-white Warbler from April 18. As with Common Yellowthroat and in contrast with the earlier species, they appear across southern NJ first, lacking that migratory line going across western NJ.

Blue-gray Gnatcatcher displays a similar pattern at the previous two species, with a fairly even distribution across southern NJ and DelMarVa, lacking any obvious concentration across western NJ.

One final pattern has emerged from looking at recent sightings of Summer Tanager and Blue Grosbeak. Let’s start first with Blue Grosbeak. If we look at the early sightings (as of April 18), we see a relatively even distribution northward across the eastern US, but then there is an obvious spurt of sightings up the easternmost coast, from Virginia up through Delaware, NJ, and into Long Island. Could it perhaps have been due to some weather anomaly? If so, I’d expect that coastal extension to disappear or to even out over the next week or so. That doesn’t happen. Instead, a week later, the relatively even distribution occurring across the eastern US remains, as does that coastal extension, which extends further upward now, through Connecticut and up to Massachusetts. Eight days later on May 2 the coastal sightings extend up into Canada.

Blue Grosbeak sightings through April 18. Compare with the sightings below from April 24.

Blue Grosbeak eBird sightings through April 24. It’s hard to not wonder what is causing the extension of this species up the easternmost coast.

On May 2 the tail of coastal Blue Grosbeak sightings extends all the way from Connecticut into Canada.

This pattern could easily be dismissed as a single-species anomaly, except that a very similar pattern is observed with Summer Tanager.

Summer Tanager sightings up to April 19. Note the same coastal extension as was seen with Blue Grosbeak.

Summer Tanager eBird sightings as of April 24. That coastal extension remains.

So there you have it. I don’t yet know what all this means, but there seem to be four patterns of sightings. It will be interesting to see how many species fall into these categories, and to know if the distributions occur similarly for these species each year. If anybody out there has ideas for why they are occurring, I’d love to hear them. Send your comments to greg@birdquiz.net.