• Deborah Allen and Robert DeCandido PhD

More NYC Pine Siskins: Irruptive, Nomadic Seed-eaters [Part 2 - 1989-2020]

Updated: Nov 3


Pine Siskin, New York Botanical Garden (the Bronx), 12 November 2008


28 October 2020


Bird Notes: Daylight Savings Time ends this weekend, so set your clocks back on Saturday night into Sunday morning. OWL WALK - we are considering one to start at about 5:00pm on Wednesday or Thursday of next week, 4-5 November. We had originally planned for Monday evening but the forecast for Mon-Tue is for cold weather and strong winds from the north. The owl walks will be in the North End of Central Park on Thursday November 5th (meet 4:30pm) and Sunday evening 8 November (meet 4:30pm) - both walks meet at 106th street and 5th Avenue - see the SCHEDULE page of our web site fr details. We are after a pair of Barred Owls. We'll do our best to bring them to a perch in the open for great photo ops.


Black-capped Chickadee, Central Park (Turtle Pond), 25 October 2020 by Deborah Allen

Nearly half of all North American bird species breed in the boreal forest, so understanding why and when (the periodicity) of large southbound movements (irruptions) is a topic of some importance. Without a doubt these irruptions are related to climate, but how? In this Newsletter we present some local numerical counts of Pine Siskins during the 2008 irruption year, as well as the abstract/discussion of a 2015 scientific paper on how climate drives seed-eating boreal birds to our area from north to south, and also from west to east. The Pine Siskin is not "showy," but it is amazing to understand how climate (cool and wet, vs. warm and dry) affects food supplies of the boreal forest driving nomadic seed-eaters to our area. Birds such as Evening Grosbeaks, White-winged Crossbills and Pine Siskins migrate by day probably because they stop to feed along the way - but recently, Pine Siskins were found to also migrate at night, as goldfinches are known to: https://tinyurl.com/y59zqujt


Pine Siskin, Pelham Bay Park (the Bronx), 27 October 2020 by Deborah Allen

In this week's Historical Notes we present 1989-2020 information/observations about the Pine Siskin in the NYC-LI-tristate area. Some of the information comes from published scientific articles, as well as anecdotal counts of numbers of migrants seen per hour (or day) at established migration watch site: (a) the % occurrence of the rare green morph (https://tinyurl.com/yxvrp4mr) Pine Siskin in flocks of "normal" plumaged birds; (b) a Pine Siskin banded in Pennsylvania in 2009 turning up four months (and 2,000 miles) later in Alberta, Canada; (c/d) October 12, 13 and 20 (2008) counts of migrating Pine Siskins in Westchester County, as well as Lighthouse Point (New Haven) Connecticut; (e) 9 November 2008 counts of migrant siskins in New Jersey; (f) 30 October 2018 counts of migrating siskins (and Purple Finches) on Long Island; (g) October 25-26 (2008) big days of Pine Siskins in Central Park; (h) 2 November 2008 migration counts of Pine Siskins on Staten Island and in New Jersey; (i) a 2015 article on the importance of climate (cool/rain) causing a failure of conifer seed crops that drive boreal seed-eating birds south (including Pine Siskins) - and an interesting investigation of what drives seed-eating birds south, and also west to east; finally (j), a 2017 paper on the ages, timing of migration and condition of migrating Pine Siskins banded at a landfill (the Meadowlands) in New Jersey.

Nelson's Sparrow, Central Park Pinetum on Tuesday 27 October (above), Deborah Allen.


Some Comments on Nelson's Sparrow: In fresh plumage (fall) has an orange throat, upper breast, and flanks and a weak malar. The malar is the short throat stripe closest to the throat bordering it on either side. The upper breast and flanks have dark streaks, these streaks being strong and distinct on the mid-western and northern Canadian subspecies of Nelson’s, blurry on the eastern subspecies of Nelson’s Sparrow (Ammospiza nelsoni subvirgatus). According to Beadle and Rising the mid-western (Ammospiza nelsoni nelsoni) and northern Canadian (Ammospiza nelsoni alterus) are “indistinguishable” in the field. Chris Elphick, posting on the Connecticut listserve ctbirds, has suggested that hybrids between Nelson’s and Saltmarsh may resemble the mid-western subspecies of Nelson’s Sparrow. The very similar Saltmarsh Sparrow has a whiter upper breast with more distinct streaking, a stronger malar, and is less orange on the throat. Deborah Allen

Black-throated Green Warbler (female), Central Park, 25 October 2020 by Deborah Allen

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Bird Walks for late October

All Walks @ $10/person - All walks in Central Park

Directions to All Meeting Locations can be found here


1. Friday, 30 October at 8:30am - [CANCELLED DUE TO FORECAST OF RAIN] Conservatory Garden at 105th street and 5th Avenue. Walk down the front (main) steps and straight ahead by 150 feet to the area between the men's room (on the right/north) and ladies' room (left/south) $10


2. Saturday, 31 October at 7:30am and again at 9:30am - Boathouse Cafe; 74th street/ East Drive $10


3. Sunday, 1 November at 7:30am and again at 9:30am - Boathouse Cafe; 74th street/ East Drive $10 - Standard Time begins as Daylight Savings Time ends


4. Monday, 2 November at 8:30am - Strawberry Fields (Imagine Mosaic) at 72nd St. and Central Park West $10


5. OWL WALK - Thu Night, 5 November at 4:30pm - meet at 106th street and 5th Ave for BARRED OWLS (yes plural) at NIGHT. $10. See SCHEDULE page of this web site for details!


If you do the 7:30am walk you can do the second (9:30am walk) for free. You get two for one. Weekend walks will continue through August and into December. Monday walks at 8:30am begin on Labor Day, 7 September and will continue through the end of October. Friday morning walks start 25 September and through October at least. What are you waiting for?


Call (718-828-8262) or Email us with questions: rdcny@earthlink.net

Red-tailed Hawk (adult); Central Park (Belvedere Castle) on 25 October by Deborah Allen


The fine print: Our walks on weekends meet at 7:30/9:30am at the Boathouse Restaurant (approx. 74th street and the East Drive). Please note: the Boathouse is not one of the buildings that surround the nearby Model Boat Pond - people make this mistake all the time! Fridays we meet at Conservatory Garden; Mondays at Strawberry Fields - check the "Meeting Points" page of this web site for exact meeting location.


Our home phone is 718-828-8262...and Deborah's cell is: 347-703-5554. Email is (rdcny@earthlink.net). If you are lost and trying to get to the bird walk, call Deborah's cell phone...but remember on weekends there will be 2-3 other people calling who are also lost - please be patient. If in doubt about whether a walk will take place or not the morning of the walk: check the main landing page of this web site as well as the "Schedule" page - if the walk is cancelled, information will be posted there by 6am the day of the walk, and usually by 11pm the night before. If still confused and as a last resort, call us at home - if no one answers it means we left for the bird walk. We end all our Central Park walks (except Fridays) near the Boathouse at about noon; you can get a cup of coffee and a muffin there (around $6 total) - though the Boathouse is closed right now and will re-open in April 2021 according to the owners. Walks last about 3 hrs (less if hot or rainy), and you can leave at anytime - we won't be offended. If you need directions/help to your next destination, just ask someone on the walk - we aim to please.

Magnolia Warbler (first fall) in Central Park on 9 October 2020 by Deborah Allen


Here is what we saw last week (brief highlights)

Friday, 23 October 2020 (Conservatory Garden at 8:30am): was a total wash-out. It rained (well misted) most of Friday morning...


Deborah's List of Birds for Friday, 23 October: No Bird Walk - RAIN today!


Sat-Sunday, 24-25 October 2020 (Boathouse Restaurant at 7:30am and again at 9:30am): Please note: the bathrooms at the Boathouse are NOT open. However, we do pass two other sets of bathrooms on the walk. Saturday, 24 October: 6 warbler species seen today including a Black-throated Blue, but our best species was only briefly seen by all: a Yellow-billed Cuckoo flew into the tree adjacent to Belvedere Castle while I was playing the alarm calls of a vireo. It then sat motionless - and everyone got a good look at it, as it flew away about two minutes later. Also this morning, wonderful Pine Siskins coming in from the blue to land near us (and on us) at Shakespeare Garden and the Pinetum; and a flock of Purple Finches also at Belvedere. On 25 October (Sunday) a flyover male Northern Harrier and a few minutes later, a second year Bald Eagle. The overnight winds had brought in more Red-breasted Nuthatches, Pine Siskins - and lots of Black-capped Chickadees. The best bird of the day was a Great Crested Flycatcher that was perched atop the White Pine tree in Shakespeare Garden.


Deborah's List of Birds for Saturday, 24 October: https://tinyurl.com/yxzmgnwp

Deborah's List of Birds for Sunday, 25 October: https://tinyurl.com/y4t49fvc


Monday, 26 October 2020 (Conservatory Garden at 8:30am): was another wash-out. It rained (well misted) most of Monday morning...


Deborah's List of Birds for Monday, 26 October: No Bird Walk - RAIN today!

Pine Siskin, Central Park (Shakespeare Garden), 25 October 2020 by Deborah Allen

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HISTORICAL NOTEs

PINE SISKIN - RECENT INFORMATION


The Occurrence of Green-morph Pine Siskins in the Siskin Irruption of 1989-1990

An intense, nearly continent-wide irruption of Pine Siskins (Carduelis pinus) began in August 1989 and continued through the 1989-1990 winter (see numerous field reports in American Birds, Vol. 44(1) through Vol. 44(5)). Siskins penetrated as far south as the Gulf States and Florida in the East, and at record early dates in Texas. In many areas they lingered into April and May, later than usual. In some Midwestern states, they lingered into the following summer. Only in the Southwest and the Pacific Coast states was there little evidence of their appearance. At three feeder/banding stations in the Schenectady, New York area, I banded 4,045 Pine Siskins between January and June 1990 and assessed the occurrence of the rare green morph of this species

Birds fitting the following descriptions from McLaren et al. (1989) of the green morph were noted. They described this morph as follows: (1) "Dark grayish-green on the back, with strong yellow wing and tail patches, a greenish- yellow rump, and tinged with yellow on the head and underparts." (2) "These greenish Pine Siskins look like ordinary ones that have lost their heavy brown streak, revealing an underlying pattern of gray and yellow that blend into green hues overlaid by a fainter remnant of the original streaking." (3) "Green morphs always lack the heavy, dark streaks usual in brownish Pine Siskins, and some have almost no streaking below. When present, the streaks appear broad and diffuse..."

Overall, the total occurrence of green-morph siskins was 1.26 percent. This compares reasonably with McLaren et al.'s (1989) finding of about one percent. They examined 1,525 specimens from six museum collections, finding 15 green morphs (0.98 percent). It was at this time of return migration [April-May] that occurrence of these green morphs was at its peak

It would be helpful for banders and field observers to record more data on green-morph siskins in subsequent invasions to assess whether their occurrence varies geographically as well as temporally; and at the same time, to take heed of McLaren et al.'s (1989) excellent advice on separating Eurasian Siskins (Carduelis spinus) which might occur in these invading flocks of Pine Siskins.

Robert P. Yunick 1527 Myron Street Schenectady NY 12309-4223

North American Bird Bander: 21(3): 85-87 (July-September 1996) - excerpts


Pine Siskin, Central Park (Pinetum), 25 October 2020 by Deborah Allen

Pine Siskin banded in Northampton County, Pennsylvania, found in Alberta, Canada From: Paul H Karner 9 August 2009


I received from the BBL data on a Pine Siskin that I banded in my yard here in Bangor, Pa. on 15 March 2009. It was found on 27 July 2009 just south of Edmonton, Alberta, Canada. This is just under 2000 miles in a straight line! So just how many miles did this Pine Siskin (PISI) fly? I'm delighted with this recovery. This is my first return on one of the 453 PISI I banded in 2009. Will any of these banded PISI's return to my yard this coming season?


Paul H Karner Bangor, PA. 18013 Cavity Nesters of Northampton County

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Major Pine Siskin movement - Westchester County (October 2008)

From: Cameron Rutt

Date: Monday 13 October 2008

Apparently, the past few days have brought a surge of Pine Siskins throughout the region, from the New England states to at least Pennsylvania and New Jersey, with seemingly fewer birds reported south of there. Chestnut Ridge Hawk Watch, near Bedford, Westchester County, had its first Pine Siskins of the season on Saturday (10/11) with 20 birds in 3 flocks. The siskin count increased yesterday (10/12), when 175 birds were conservatively recorded in 7 passing flocks.

However, both of those days fell short of the massive movement that took place all day today at Chestnut Ridge. Shortly after I arrived at the hawk watch this morning, a calling flock of approximately 60 birds flew directly overhead, the first sign of what would be an impressive passage of birds. Tait Johansson joined me up at the watch and together we counted/estimated the knots of flyby siskins, reaching a final tally of 2,524 birds! Altogether, 73 flocks were noted with flock sizes ranging from 2 to 133 individuals. Among the more noteworthy flocks were groups of 90 (twice), 85, 80 (twice), and 75 birds. The average flock, though, was about 35 birds strong. Siskins continued flying until shortly after 5:00 PM (DST) with a flock of 90 at 5:05 and 3 more at 5:20. With the addition of Lighthouse Point's and Quaker Ridge's siskins today, 6,204 were amassed between these three hawk watches.

Hour-by-hour count (starting with the 9:00-9:59 AM hour DST): 223, 502, 84, 249, 205, 319, 268, 581, and 93.

Other regional high counts from the past two days:

12 Oct 2008:

265 - Pack Monadnock, NH

500+ - Blueberry Hill, MA

78 - Lighthouse Point, CT

140 - Montclair, NJ

79 - Hawk Mountain Sanctuary, PA

13 Oct 2008:

~265 - Blueberry Hill, MA

780 - Quaker Ridge, CT

2,900 - Lighthouse Point, CT

~450 - State Line Lookout, NJ

140+ - The Celery Farm, NJ

Good Birding,

Cameron Rutt

Katonah, Westchester County

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Pine Siskin flight continues - Westchester County (October 2008)

From: "Cameron Rutt"

Date: Monday 20 October 2008

Echoing what both Ken Feustel and Matt Young pointed out in recent days about good numbers of Pine Siskins, Chestnut Ridge (near Bedford, Westchester County) has continued to have some impressive siskin flights. Today's flight of over 1261 birds (in 62 flocks) was this site's second major push for siskins this fall. Today's noteworthy passage came exactly one week to the day after the more sizable siskin push on 10/13 (2524).

Today's hour-by-hour count (starting with the 9:00-9:59 AM hour DST):

111+, 132, 269, 22, 123, 70+, 182, 352

Two flocks were heard only, thus the "+" in the hourly breakdown. I found it interesting that in our four best siskin days, the mid- to late afternoons have been especially productive. In fact, on our two best days (10/13, 10/20), the 4-5 PM hour has had the most siskins of any hour in that day. Finch flights are typically something that I associate with early mornings.

Additionally, today's average flock only contained about 21 birds each, this compared to 35 bird flocks a week ago. Ken Mirman, Tait Johansson, and I have continued to keep track of the Pine Siskins at Chestnut Ridge over the past week. With today's addition, this makes 5211+ Pine Siskins (201 flocks) in the last week and a half (10/11-10/20)!

10/11 - 20 (3 flocks)

10/12 - 175 (7 flocks)

10/13 - 2524 (73 flocks)

10/14 - 92 (4 flocks)

10/15 - 31+ (3 flocks)

10/16 - 7 (2 flocks)

10/17 - 152+ (10 flocks)

10/18 - 446 (15 flocks)

10/19 - 503 (22 flocks)

10/20 - 1261+ (62 flocks)

Finally, Lighthouse Point, CT, has continued its Pine Siskin onslaught with back-to-back days of 1340 (10/19) and 1300 (10/20) birds.

Good Birding,

Cameron Rutt

Katonah, Westchester County

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Subject: Lighthouse Sunday October 19 (Pine Siskinetics)

From: REBECCA I HOROWITZ

Date: Sunday 19 October 2008

259 diurnal raptors with strong NNE winds and plenty of cloud cover. The weather folks predicted 0% clouds which would have been a disaster for counting.

The Pine Siskin movement was spectacular. The totals below were mostly comprised of early morning fly-overs, and as siskins went through in flocks of 10-100, other birds were swirling everywhere. Many went uncounted as I tried to focus on the hawks.

4 RT Loon, 25 Com Loon (including a single flock of 23!), 2 Great Egret, 63 Canada Goose, 7 Brant, 5 scaup sp., 1 Chimney Swift, 88 Blue Jay, 621 Tree Swallow, 12 American Pipit, 4 Palm Warbler, 11Yellow-rumped Warbler, 609 Red-winged Blackbird, 79 Common Grackle, 131 Brown-headed Cowbird, 160 unid. Blackbird, 13 Purple finch, 4 House Finch, 1340 Pine Siskin, 355 unid. finch (distant flocks resembling those of Pine Siskins, and almost certainly Pine Siskins).


Pine Siskin, Central Park (Pinetum), 25 October 2020 by Deborah Allen

Subject: Impressive siskin flight at Jones Beach (November 2008) From: Seth Ausubel Sunday 9 November 2008 I estimated 4,200 pine siskins in this morning's flight at Jones Beach West End, from 7:30-9:45. There were flocks of several hundred birds at time alighting in the pines at the turnaround. Other birds in the flight were approximately 1700 American goldfinches, 900 American robins, 650 red-winged blackbirds, 500 cedar waxwings, and 50 purple finches. No crossbills. A dickcissel was around the exit ramp of the West End 2 parking lot north of the pavilion, and 2 vesper sparrows were in the median near the cottonwood tree. There are at least 2 tufted titmice around, probably more. Seth Ausubel Forest Hills, NY

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Subject: Cave Swallows and Pine Siskins - Montclair NJ Hawk Lookout (Essex Co.) From: Justin Bosler Sunday 9 November 2008 Hello JerseyBirds, I haven't done too much perusing of the listservs yet, but there must've been a considerable flight of Cave Swallows across the region today, 9 November. It was certainly the type of November weather that results in a flight of Cave Swallows along the Atlantic seaboard as they are pushed eastward by post-front westerly winds. At 2:35 PM, I spotted 2 swallows zipping around to the ENE fairly low over the eastern slope of the ridge. After several seconds of frantic scanning, I was treated to nice scope views of 2 CAVE SWALLOWS. I lost track of the swallows shortly thereafter as I went for my camera, however, both swallows presumably continued downridge as I last saw them flying in that general direction (more or less toward the hawkwatch platform). The PINE SISKIN irruption continues with a new single-day high of 890+ passing the Lookout today. Although to a lesser extent, PURPLE FINCHES are also staging a southward irruption. Today's 100 was relatively unimpressive after a few late October single-day counts exceeding 150 birds. Singles to small flocks are the norm with the largest flock numbering 38 birds. Today's highlights of 77 individual raptors include singles of NORTHERN GOSHAWK, AMERICAN KESTREL, and MERLIN.

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Subject: Astonishing Purple Finch and Pine Siskin Irruption Continues

30 October 2018

From: Shaibal.Mitra PhD

Favorable northwest winds produced another huge flight this morning at Robert Moses SP, Suffolk County. Species diversity is dropping as Neotropical migrant species drop out of the mix, but the most numerous medium-distance migrants are at high abundance: 10,000 Myrtle Warblers, 2,690 Pine Siskins, 1,320 American Goldfinches, 1,175 Red-winged Blackbirds, and 1,077 American Robins in two hours. But the most mind-bending thing was the crush of Purple Finches, a species that is often more numerous on passage than many birders appreciate, but which nevertheless is a bird I expect in no more than scores or hundreds per day, even in flight years. I thought my first hour this morning was good, with a total of 276, but during the next hour, things got strange. More than once I had to abandon my sample counts of Myrtle (Yellow-rumped) Warblers and other species in disbelief as my scans revealed individual flocks of 100+ Purple Finches in view at once; the one-hour total for 09:30-10:30 was 1,940!

I had to leave it at that, with the finches continuing in huge numbers. The ocean was teeming with gulls, gannets, seaducks, and cormorants but had to be neglected.

Shai Mitra

Bay Shore, Long Island

Pine Siskin, Central Park (Pinetum), 25 October 2020 by Deborah Allen

Pine Siskin, Central Park (Pinetum), 25 October 2020 by Deborah Allen

2008: Saturday, 25 October (New York Botanical Garden in the Bronx) – before the walk, Debs and I wandered around with our Ipod playing finch calls - and bringing in a group of 15 or so Pine Siskins to feed in crab apples atop at hill opposite the Conservatory. And from experience, we knew NYBG is the best place locally to find Red-breasted Nuthatches. Playing their song via our speakers, we brought in 3-4 Red-breasted Nuthatches before the walk. And once we had gathered everyone up, we managed to bring in a few more Red-breasted Nuthatches. Most notably, while we played the Ipod just outside the native plant garden, we brought in a lone Pine Siskin that perched (in the shade) just over my head. Finally, for those of you interested in mammals, the Beaver still has a lodge along the Bronx River, but I am finding more and more gnawed trees over on the zoo side of the river. We will be back to NYBG on one of the next few Saturdays to find more finches and Red-breasted Nuthatches, as well as search for the local pair of Great Horned Owls. 2008: Sunday, October 26th (north end Central Park) – This was one of the great all time autumn walks...When I left my Bronx home at 6:30am, a Merlin was swooping and chasing birds in my neighborhood. When I arrived at the park, in the moderate northeast winds, there were flocks passing overhead of Common Grackles, Red-winged Blackbirds and Brown-headed Cowbirds. Occasionally there were smaller birds traveling in tight balls and these we discovered were Pine Siskins. (American Goldfinches have not been common so far this autumn in the park.) Standing in the southern part of Conservatory Garden at about 8:30am, I began playing the Pine Siskin call to a flock of small birds hidden in a somewhat distant Red Oak. Almost immediately the flock flew down into a Japanese Lilac tree a few feet away. People from the walk began to arrive as well...and in the ensuing minutes (until about 9:20am), more Pine Siskins continued to arrive and perch in the lilac tree. The birds were calling to one another (and my tape). Soon, a few began to land in a still-blooming pink rose bush about five feet from us. And then the amazing began to happen - groups of 3-5 birds would fly down and hover over us, and one bird actually landed and sat on my head (luckily I was wearing a hat). We estimated about 200 Pine Siskins mulling about the area...and as our group expanded in number to about 25 people, I could hear the ooohs and aaahs as they watched the siskins fly down and around us, and then disperse into the nearby trees. Amazing...So later it almost seemed like a let down when we found a lone Purple Finch, two Blue-headed Vireos, two Palm Warblers (+ several Yellow-rumps), as well as the first Buffleheads (two females) of the season. One last note: on sparrow hill (at the northeast corner of the north end baseball fields), we were standing near a pine tree with no birds in sight. I decided to play the Pine Siskin call, and within 30 seconds, a flock of 25-50 zoomed down from a clear blue sky to land in that pine tree! Folks were amazed. Basically, my interpretation is this: for nomadic birds looking for feeding areas, hearing the calls of happy cohorts is a strong suggestion that appropriate conditions (food, water, safety) are nearby so they come over to have a look.

Black-capped Chickadee, Central Park (Turtle Pond), 17 October 2020 by Deborah Allen

Pine Siskins on Staten Island (2008) Date: Sunday 2 November 2008 Grymes Hill / Wagner College

Clove Lakes Park at 8:30am: Early this morning a number of Pine Siskins flew over and some were feeding in spruces on Pleasant Valley Ave. In total, there were more than 100 birds in small flocks, and one larger flock numbering ~ 60 birds. At CLP near the dump and tower there were 8 Purple Finches, one of which was an adult male. About 100-150 Pine Siskins were also flying over the park moving in a westerly direction. H. Fischer ================================ Pine Siskins Celery Farm New Jersey (2008) Date: Sunday 2 November 2008 On a brief walk with the family this morning. At 10:30 we came upon a very active and vocal flock of Pine Siskins (30 to 40, rather difficult to count) feeding in the leaves and the underbrush all along Allendale Brook, north of the Pirie Platform. The birds came quite close (they were pretty hungry) and we got some great views. (Great auditory experience: “zrrrrrrrreeeeeeeeeee!") Also had a few Siskin flyovers at the Greenway entrance. John Workman Ridgewood, NJ

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Climatic dipoles drive two principal modes of North American boreal bird irruption (2015)

Courtenay Strong, Benjamin Zuckerberg, Julio L. Betancourt, and Walter D. Koenig


ABSTRACT. Pine Siskins exemplify normally boreal seed-eating birds that can be sparse or absent across entire regions of North America in one year and then appear in large numbers the next. These dramatic avian "irruptions" are thought to stem from intermittent but broadly synchronous seed production (masting) in one year and meager seed crops in the next. A prevalent hypothesis is that widespread masting in the boreal forest at high latitudes is driven primarily by favorable climate during the two to three consecutive years required to initiate and mature seed crops in most conifers. Seed production is expensive for trees and is much reduced in the years following masting, driving boreal birds to search elsewhere for food and overwintering habitat. Despite this plausible logic, prior efforts to discover climate-irruption relationships have been inconclusive. Here, analysis of more than 2 million Pine Siskin observations from Project FeederWatch, a citizen science program, reveals two principal irruption modes (North-South and West-East), both of which are correlated with climate variability. The North-South irruption mode is, in part, influenced by winter harshness, but the predominant climate drivers of both modes manifest in the warm season as continental-scale pairs of oppositely signed precipitation and temperature anomalies (i.e., dipoles). The climate dipoles juxtapose favorable and unfavorable conditions for seed production and wintering habitat, motivating a push-pull paradigm to explain irruptions of Pine Siskins and possibly other boreal bird populations in North America.


DISCUSSION: We decomposed patterns of Pine Siskin irruptions into two continental modes: a North-South Irruption Mode with prominent irruptions in 1990 and 2009 and a West-East Irruption Mode with biennial fluctuations before 1998 followed by more erratic temporal variability. In contrast to prior studies, we uncovered statistically significant and physically plausible climate drivers for each irruption mode. Most of the climate drivers were precipitation or temperature effects preceding the winter FeederWatch observation season by 1 or 2 years, and the success of the statistical models presented here indicates that irruptions may be predictable. Any such increase in predictability would potentially provide an opportunity to understand irruptions better through the marking and subsequent following of birds during irruption events. It might further facilitate the ability to detect their ecological consequences, which, like other pulsed phenomena, are potentially significant.


For both irruption modes, the predominant climate forcing had a dipole spatial structure, meaning that the climate forcing tended to produce an unfavorable seed crop over one region (cool-wet forcing) and a favorable seed crop over another (warm-dry forcing). Although hypotheses for avian irruptions have generally focused on a sequence of conditions leading to the demographic consequences of food shortages in the region from which birds migrate, our results are more consistent with a pushpull paradigm in which anti-phased climate anomalies (dipoles) modulate broad-scale irruptions by creating unfavorable conditions in one region and more favorable conditions in another.


The pull of irruptive migrants and settlement in a region could result from social cues in decision making, such as conspecific attraction, for choosing suitable wintering habitat. Based on our findings, however, this dynamic is probably stronger for the North-South Irruption Mode than it is for the West-East Irruption Mode. For the western United States, there was some tendency for above-average Pine Siskin counts during North-South irruption, yet climate in this region did not strongly correlate with the North-South Irruption Mode index. This lack of a straightforward climate connection suggests that a component of western US irruption is more push than pull (i.e., some Pine Siskins migrating south from unfavorable conditions in the boreal forest arrive in the western United States even though conditions in this region are not especially favorable). However, conclusions about the mountainous western United States are complicated by relatively low observation densities in the FeederWatch data, strong elevation gradients, heterogeneity in conifer masting, and underlying fluctuations in local resident bird populations.


The climate drivers of Pine Siskin irruptions are regional manifestations of larger scale climate patterns. The precipitation dipole underlying the North-South Irruption Mode is similar to a dipole pattern other studies have identified as the leading mode of annual mean precipitation variability over eastern North America, and the winter air temperature driver of the North-South Irruption Mode is correlated with the North Pacific Index (r = .0.50, P < 0.05). The North Pacific Index is linked to hemispheric modes of decadal circulation variability and tracks sea level pressure variations that strongly influence temperature extremes. The precipitation and temperature dipoles associated with the West-East Irruption Mode are, in part, driven by a pan-Pacific atmospheric wave pattern emanating from Asian monsoonal convection, and similar warm-season climate dipoles have been more generally linked to Rossby wave-like structures guided by the mean jet streams over North America and Asia.


Nearly half of all North American birds breed in the boreal forest, and as such, the periodicity of avian irruptions, and their connection to climate, likely represents a critical bellwether of how climate variability influences North American biota. Climate change may alter the strength, periodicity, synchrony, or orientation of the irruptive patterns identified here because future changes in spring and summer precipitation are projected to exhibit varying dipole patterns over North America. The implication for species that display strong variability in population dynamics (irruptions and cycling) may be a future characterized by uncertain changes in climate and resources. We were able to uncover linkages between climate and continent-wide avian irruptions by leveraging rich data from an international citizen science program and making mechanistically consistent inferences on regional seed crop variability. Deeper understanding of these correlations will be possible as more comprehensive spatio-temporal data, particularly on seed production, become available. Finally, precipitation and temperature dipoles are common and well-known features in the climate system, and their influence could extend well beyond boreal bird irruptions to explain a broad suite of important biogeographic phenomena.

Evening Grosbeak (male) Algonquin National Park (Ontario, Canada), 30 January 2016


Passage Dates, Energetic Condition, and Age Distribution of Irruptive Pine Siskins during Autumn Stopovers at a Landfill in the New Jersey Meadowlands (2017)

Chad Seewagen and Michael Newhouse


Abstract. Little is known about the stopover biology of Spinus pinus (Pine Siskin) and other Fringillid birds during their irruptive movements into the US from boreal Canada. Here, we report on the passage timing, energetic condition, and age distribution of 402 Pine Siskins that we captured during autumn stopovers in New Jersey in the irruption year of 2012. Pine Siskins passed through our study site for ~3 weeks and peaked in abundance between 9 and 12 October. More birds were juveniles than adults (54% v. 46%), although the difference was not significant. Juveniles were heavier than adults, but fat scores did not differ by age. Neither age group appeared to gain significant mass during the stopover. We encourage migration banding stations like ours that experience irruptions to report the information they collect and help improve our understanding of the migration biology and behavior of irruptive species.


Results and Discussion [excerpts]. We captured all 402 Pine Siskins during the fall 2012 season between 3 and 26 October. By comparison, we captured only 20 Pine Siskins at our station during 2010, 2011, and 2013 combined (all of which occurred in 2010). Peak passage during the irruption was during 9 to 12 October 2012, when we caught 253 (63%) of the 402 Pine Siskins. Capture rate was highest on 12 October (255 birds/100 net h) and

substantially greater than on any other day (Fig. 1). Approximately 70 km east of our site, Ausubel (2013) noted that peak passage of Pine Siskins through Robert Moses State Park on Long Island, NY, in 2012 also occurred in mid-October, and a record number of individuals were counted on the 21st of that month. Pine Siskins peaked in abundance in Kiptopeke, VA, approximately 435 km south of our study site, 1 to 2 weeks later between late October and early November that year (Kolbe and Brinkley 2013). At the Powdermill Nature Reserve [Pennsylvania], Pine Siskins were first captured on 6 October and last captured on 14 November during the 2012 irruption. The peak there occurred on 2 November, ~3 weeks later than the peak at our study site, when 58% of the 326 Pine Siskins banded that season were captured. No more than 10% of the total number of Pine Siskins banded for the season was captured on any other single day. Peak passage at the Powdermill Nature Reserve was slightly earlier during the 2014 irruption year, when 53% of the 163 Pine Siskin captures occurred from 20 to 26 October and another 25% occurred 4 days later on 30 October. From these observations throughout the region, it appears to take waves of irruptive Pine Siskins ~3 weeks to move from the latitude of southern New York State and northern Pennsylvania into the northern mid-Atlantic area and Allegheny Mountains. It also appears that coastal migrants might move ahead of or faster than inland migrants, given that peak passage at the Powdermill Nature Reserve in

western Pennsylvania during the 2012 irruption occurred around the same time as it did ~435km to the southeast, in Kiptopeke, VA.


We captured more juveniles than adults (54% v. 46%), but the difference was not significant (Chi-square = 2.6, P = 0.11). However, Pine Siskin age distribution at Powdermill Nature Reserve was significantly skewed towards juveniles during the 2012 (Chi-square = 22.6, P < 0.0001) and 2014 (Chi-square = 77.3, P < 0.0001) irruptions. This result could be the result of adults tending to follow coastal routes and/or juveniles tending to follow inland routes, but the opposite pattern is usually observed among passerine migrants (e.g., Morris et al. 1996, Murray 1966, Ralph 1981; but see Mills 2016). Age differences in the irruptive migratory behavior of Pine Siskins have not been studied, to our knowledge, and are an interesting topic for future investigation.

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Deborah Allen and Robert DeCandido PhD

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Black Baza (female) on migration in eastern Thailand 31 October 2011


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@2020 ROBERT DECANDIDO, PhD