October 2019

Fall Migration and Other Movements of Maine Birds

By in Migration, Weather

Migration is a phenomenon in which members of a species move seasonally and predictably from one region to another. The fall migration is a time of loss for us. We bid farewell to our Eastern Phoebes as they head to Florida, our Ruby-throated Hummingbirds as they depart for Costa Rica and even Monarch butterflies as they begin to wing their way to the highlands of Mexico.

Of course, fall does offer us the chance to see birds that neither breed nor winter in Maine. These passage migrants delight us as they pass through Maine en route to wintering areas to the south. Common passage migrants include many species of sandpipers and plovers and White-crowned Sparrows.

Two common passage migrants in the fall are the Cape May Warbler and Fox Sparrow. These species are uncommon nesting species in most of the state; most of their breeding ranges are to the north of us. So, it is easier to find a Cape May Warbler or Fox Sparrow during the fall than it is during the nesting season.

We have three other types of autumn movements in birds that don’t qualify as true migrations. First, we have birds that are storm-tossed. Land birds are pretty good at hunkering down during hurricanes and tropical storms so most vagrants displaced by storms are seabirds, hawks and falcons.

Some species undergo post-breeding dispersal in the late summer and fall, movements typically involving moving north. Herons, egrets and Ospreys commonly engage in these movements. The explanation for these movements in the “wrong” direction are unclear. Some ornithologists have suggested that these birds are prospecting for new and better nesting areas for use in future years. It is clear that these movements are hard-wired in these birds as this dispersal occurs predictably. Eventually these birds do head south for the winter.

The final type  of movement is called reverse migration and represents an error in navigation. Some birds have their internal compass reversed so north seems to be south. Reverse migration may explain the appearance of southern or western birds in the northeast, far from their typical geographic range.

We have had some remarkable bird sightings in Maine this fall that can’t be explained by migration. Let’s review some of them and try to understand why these vagrants appeared in Maine.

On September 15, a Swallow-tailed Kite was seen in Dennysville in eastern Washington County.  This unmistakable bird, mostly white with black on the back, wings and the forked tail, was gone the following day but local non-birders had apparently seen it as early as September 7. The date corresponds with the passage of the remnants of Hurricane Dorian, which hit Washington County harder than the rest of Maine. There are only six accepted state records of this species, mostly from southern Maine.

In the past three weeks, small numbers of Black Skimmers have been reported at several coastal locations as far north as the Schoodic Peninsula. They do nest as far north as Massachusetts. Are these post-breeding dispersers? The fact that so many have appeared in Maine would seem to rule out reverse migration as an explanation and we experienced no strong storms in the past three weeks. Perhaps these are birds that were pushed into the Maritimes by Hurricane Dorian and are working their way back south. The number of fall records is far greater than in other autumns in my memory.

Royal Terns, Caspian Terns and even a Gull-billed Tern have appeared widely as well, often in loose association with the Black Skimmers. Post-breeding dispersal seems the likeliest explanation but we can’t know for sure.

And now for something completely different. A Townsend’s Solitaire appeared on Monhegan Island on October 5.. This species belongs to the thrush family and they breed in western North America. Since land birds are not typically storm-tossed, post-breeding dispersal in a big way or reverse migration are possible explanations.

Fall birding in Maine. You gotta love it!

Amateur Ornithology and iNaturalist

By in Software Tags:

Amateurs have made tremendous contributions to North American ornithology. I cannot think of any other branch of science in which non-professionals have contributed so substantially.

Surgeons in the U.S. Army Medical Corp stationed in the western states in the later part of the 19th century extended our then scanty knowledge of the western birds. Some of these men are commemorated in the common names of birds they studied: Heerman’s Gull, Bendire’s Thrasher and Coues’ Flycatcher (now Greater Pewee).

Margaret Morse Nice moved to Ohio in 1927 when her husband accepted a professorship at Ohio State University. From 1929 until 1937, Margaret studied banded Song Sparrows on their farm. The detail of her observations and the time she devoted to the project were phenomenal. Her work provided great insight into territoriality, nest-site fidelity, behavioral interactions and song.  Nice’s work was pivotal in moving ornithology from a shotgun-based approach to a binoculars-based approach.

Amateur observers have been essential for two of the most powerful census projects we have of North American Birds. The National Audubon Christmas Bird Count, begun in 1900, relies primarily on amateur birders. The North American Breeding Bird Survey (BBS), begun in 1966, relies heavily on skilled amateurs as well. The BBS data clearly alerted us to the dramatic decline in Neotropical migrant birds like many of our warblers, vireos and flycatchers.

The development of the internet has facilitated sharing of bird observations. I have written of the value of eBird as a resource to examine changes in the geographic and temporal distribution of birds. eBird came on-line in 2002 and is indeed a treasure trove for ornithologists.

Although eBird allows observers to upload photographs and sound recordings to document sightings, most observers simply submit checklists. A cadre of knowledgeable birders keeps track of unusual sightings and may ask an observer for further detail. No birder is ever forced to remove a sighting but an unconvincing sighting may be excluded from the data provided to researchers.

I want to conclude this column with discuss of another web-based resource for reporting sightings of any organism. It is called iNaturalist (http://www.inaturalist.org/). This application is similar in approach to eBird but with a social-networking component.

Here’s the way iNaturalist works. You set up a free account and then click the Add Observations button. You are then taken to a window where you can upload either a picture or a sound recording of your observation. You fill in the date of your observation an indicate on an interactive map where your observation was made.

Finally, you are asked to provide the species name of your observed organism.  You might not be sure of the species but iNaturalist can help you. It has an Artificial Intelligence (AI) feature that will suggest the species name, genus name or family based on your photograph. You pick the identification that seems correct to you and post it. Your photograph will now have a yellow flag with Needs ID written on it.

Other naturalists can look now at your photograph and either confirm your identification or suggest an alternative. Once two people agree on an identification (one can be you), your photo will show a green flag with Research Grade written on it. It can then be used as a record by other researchers.

The AI feature is pretty amazing. The program continues to learn as it processes more Research Grade images. I’ve found that bird, dragonfly and butterfly identifications are usually correct. I’ve had less success with herbaceous plants and marine invertebrates.

iNaturalist will keep lists of all species you document. It’s straightforward and is a great learning tool. An app for your phone is available so it is easy to take a picture with your phone and then post your geo-coded picture to iNaturalist in a snap.  This resource provides yet one more way that amateurs can contribute to field biology.

Maine Fall Departure Dates

By in Migration, Weather

The timing of bird migration is fascinating to birders. We particularly look forward in the spring to our “first of the year” sightings of various migratory breeding birds. The fall departure of those breeding birds is equally interesting but much more poorly documented.

The explanation for the difference is a simple one. When you see your first Ovenbird of the spring, you record that date and you are done. Documenting the last departure requires continuous record-keeping. Perhaps you are able to go to birding every day in late September. On September 25 and 26, you see a Gray Catbird, none on September 26 and 27, one on September 28 and then none for the rest of the fall. You duly record September 28 as the last fall departure date but what an ordeal it was to get that date. Ideally, a birder seeking to document last departure dates should be out birding every day in the fall. As wonderful as that would be, who has the time?

To improve our understanding of the rhythm of Maine fall migration, I used the eBird database. This on-line application, administered by the Cornell Laboratory of Ornithology, is a boon for both birders and researchers. The eBird application will keep track of your life lists and generate target lists for birds you haven’t seen yet. Each birder’s sightings are available by request by ornithological researchers with approved research projects.

Between 1994 and 2017, I coordinated a volunteer-based spring arrival project so I used the same years for the departure date project for the sake of complementarity.  eBird was not launched until 2002. Some birders have uploaded data prior to 2002 onto the site but most of the 65,000 (!) records for this study came from 2002 onwards.

I had adequate data to analyze 85 species of migratory breeding birds. To examine the tempo of migration, I divided the state into three equal latitudinal bands: the North Region south to the latitudinal line through Jackman, the Central Region south to the latitudinal line through Limerick and the South Region south to Kittery. We expect that migration will proceed from north to south, reflecting the harsher climate as one proceeds northward.

The eBird data I used are simply sightings of migratory birds, not necessarily last departure dates. To extract last departure dates, I had to define a beginning  and ending point for each species.

I used the Last Safe Date from the Maine Breeding Bird Atlas to define the beginning of fall migration for each species in the study. Any observation later than the Last Safe Date cannot be used as evidence of breeding for a species because fall migrants will already have started to pass through the state. The end of fall migration was defined as December 31 although most species depart well before then.

I analyzed the latest 10% of dates for each species in each of the three Regions.  Of the 85 species analyzed, 64 conformed to the expected pattern: earliest departures from the North Region and latest departures from the South Region. Eleven species showed no difference between two Regions.

Ten species showed surprising patterns. Spotted Sandpipers departed last from the North Region. Nine species departed last from the Central Region. I think the explanation lies in the quality of the stopover habitat. Spotted Sandpipers likely had better staging areas in Aroostook County than in points south. It was easy to miss Spotted Sandpipers in the South or Central Region because they moved through so quickly.

Diet influenced migratory schedules. Aerial insectivores (swallows, swifts) were the first to leave, followed by leaf-gleaning insectivores (warblers, vireos) with seed-eaters (sparrows, buntings) bringing up the rear.  Seeds can be reliably found later in the fall after the insects have disappeared.

You can download a copy of my paper at: https://bit.ly/2kqMry3

  

 

Shorebirding on the South Lubec Sand Bar

By in Migration, Trip Report

            My wife and I have recently returned from a week in Lubec, the easternmost town in the state of Maine. We visited one of my favorite birding spots in the state, the South Lubec Sand Bar, several times. The sand bar is a mile-long spit, accessible from the South Lubec Road not far from West Quoddy Head. The sand bar is owned and maintained by the Maine Department of Inland Fisheries and Wildlife.

`           The bar is a regionally significant stop-over site for migrating shorebirds. Thirty years ago, this habitat hosted up to 10,000 Semipalmated Sandpipers in August and September. Such spectacular numbers of this species no longer pass through the region but the species occurs regularly by the hundreds.

A birder can form an impressive list of shorebirds by hiking to the end of the bar and back.  At low tide the birds are widely dispersed along the extensive intertidal flats, a result of the 20-foot tidal range in Cobscook Bay. Birding at low tide is therefore a fool’s errand. At high tide, the birds fly inland to roost in fields and other open areas. So, to see the most birds, timing your trip to the tidal cycle is paramount. I prefer to work the rising tide. I arrive at the bar about three hours before the predicted high tide. Within an hour, the birds are pushed near shore by the incoming tide. For the next hour, the birds are concentrated in the upper intertidal. That hour is birding heaven with the birds closely packed. As the tide pushes the birds into the upper intertidal zone where food in the mudflats is sparse, the shorebirds head for their upland roosts. Some people like to work the falling tide, arriving on site an hour or so after high tide and waiting for the shorebirds to return.

Our lists contained the usual species expected at this time of year: Semipalmated Plover, Black-bellied Plover, Greater Yellowlegs, Lesser Yellowlegs, Short-billed Dowitcher, Semipalmated Sandpiper, Least Sandpiper, White-rumped Sandpiper, Sanderling and Ruddy Turnstone. A couple of unseen American Golden-Plovers gave their distinctive, plaintive “que-del” call. Other birders found a Baird’s Sandpiper and two Western Sandpipers, both excellent finds for Maine. We were delighted to see two Marbled Godwits, the first I’ve seen in Washington County in over 30 years of birding there. We were also thrilled to see a Red-necked Phalarope foraging in the intertidal zone.

We found three Great Egrets, the first I have seen in Cobscook Bay. A female Northern Harrier put on a show over the adjacent marsh. We found no falcons although Peregrine Falcons and Merlins are often present, looking for a shorebird meal.  We have even had Parasitic Jaegers here.

You don’t have to travel Downeast to find prime shorebird habitat. Any intertidal mudflat at this time of year will likely be productive. Just use the tide to your advantage to concentrate the birds for easy viewing. Freshwater mudflats can be productive as well and you are not wedded to the tide table to plan a visit.

The tundra-nesting shorebirds we see show a staged migration, adults arriving first and then juveniles a few weeks later. The short breeding season in the arctic means that parents only have time for one brood per season.  To increase the chances of surviving another year and reproducing again, sandpipers are under pressure to begin their southbound migration as soon as possible.

            Because shorebird chicks can fend for themselves soon after hatching, the parents migrate from the breeding grounds before their young have even learned to fly!  Along the Maine coast, the first adult shorebird migrants begin showing up by the middle of July.  Juvenile sandpipers and plovers are just starting to arrive in Maine now. 

            Check your field guide to see how to distinguish adult from juveniles for each species. As a general rule, juveniles have brighter and crisper plumages.; their feathers are just a few weeks old.

 

Convergence Among Sparrows Living in Salt Marshes

By in Morphology, Physiology

Like all organisms, birds are well adapted to their environment. Birds have bills that are effective tools for gathering particular types of prey: sharp bills for tearing flesh in hawks and owls, forceps-like bills for capturing caterpillars in warblers, conical bills for crushing seeds in finches and sparrows. Bird toes and many other structures are adapted for particular functions as well.

It’s fascinating to compare birds from different parts of the world and look for similar adaptations.  For instance, our wood-warblers of the Americas are superficially similar to the Old World warblers of Africa and Eurasia. Both make a living by gleaning insect larvae from leaves using their fine bills. Yet, DNA evidence indicates that these two families of birds are not closely related. Rather each family developed thin bills independently, a process biologists call convergence.

Examples of convergence abound among the birds. For instance, the African longclaws look very similar to our meadowlarks but are distantly related. Falcons and hawks were once combined into a single family. Thanks to DNA comparisons, we know that the closest relatives of the falcons are the parrots and the songbirds and the closest relatives of hawks are the New World Vultures. These formidable predators with wicked talons, beaks for tearing and extraordinary eyesight arose independently.

In the last post, I wrote about the Saltmarsh Sparrow, the only songbird in North America that is restricted to marine habitats. However, there are some species of sparrows in which subspecies have invaded the marine environment.

A bird living in a marine environment faces serious salt-balance problems. The food they eat and any water they take in are high in salts, stressing the kidneys. Humans can’t drink seawater without dire consequences and so it is with most birds. But birds living in salt marshes have developed physiological functions to ameliorate the salt stress and other challenges

Jennifer Walsh of the Cornell Laboratory of Ornithology along with twelve co-authors have recently completed a genetic study of four sparrow subspecies that occur in tidal marsh environments. They compared each tidal marsh sparrow to its closest relatives from upland areas, free of salinity stress.

The four tidal marsh sparrows included a subspecies of Song Sparrow found only in salt marshes of San Francisco Bay, a subspecies of Savannah Sparrow found in salt marshes from Santa Barbara, California to the Baja Peninsula of Mexico, Nelson’s Sparrow found in salt marshes from Maine to the Maritime Provinces and a subspecies of Swamp Sparrow found in brackish marshes along the mid-Atlantic coast.

The comparison group for the tidal Nelson’s Sparrows was a population found in freshwater marshes in Minnesota and North Dakota. The closest relatives of the other species were within a hundred miles or so of the tidal populations.

The four subspecies of tidal marsh sparrows share three adaptations for life in those areas. First are modifications of the kidneys to deal with the heavy salt load. Second, the bills of the tidal marsh birds are larger than the bills of their upland relatives. The larger bill allows more efficient heat loss in the relatively hot tidal habitats. Finally, all tidal marsh sparrows have darker plumage than upland populations, an adaptation to reflect the intense, harmful ultra-violet radiation in the coastal environments.

The question Walsh and colleagues were seeking to answer is whether these adaptations for living in a tidal environment developed independently in the four sparrow subspecies or do they represent shared adaptations controlled by the same genes that are not activated in upland sparrows?

To cut to the chase, the research showed that these three adaptations had mostly separate genetic origins. In other words, this suite of adaptations represents four different examples of convergence to the same solutions for living in stressful tidal marshes.