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First Detection of Night Flight Calls by Pine SiskinsAuthor(s): Michael L. Watson, Jeffrey V. Wells, and Ryan W. BavisSource: The Wilson Journal of Ornithology, 123(1):161-164. 2011.Published By: The Wilson Ornithological SocietyDOI: http://dx.doi.org/10.1676/09-171.1URL: http://www.bioone.org/doi/full/10.1676/09-171.1

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The Wilson Journal of Ornithology 123(1):161–164, 2011

First Detection of Night Flight Calls by Pine Siskins

Michael L. Watson,1 Jeffrey V. Wells,2,4 and Ryan W. Bavis3

ABSTRACT.—Nocturnal migration is a commonstrategy among North American passerines. Birds of theFringillidae have typically been labeled as predominatelydiurnal migrants. We used pressure-zone microphonesand automated sound detection software to record flightcalls of nocturnally migrating birds from 2 to 16 October2008 from 2000 to 0600 hrs EST at three locations nearGardiner, Maine. We detected and recorded 190 PineSiskin (Spinus pinus) flight calls from throughout thenight at three separate locations. This is the first publisheddocumentation of apparent nocturnal migration in thisspecies. Nocturnal migration may be a facultativemigration strategy in the Fringillidae that occurs only inyears in which large irruptive movements occur as forPine Siskins in fall 2008. Received 30 October 2009.Accepted 3 November 2010.

Most North American passerines are known to

be nocturnal migrants. Theories for why nocturnalmigration is more common than diurnal migrationamong passerines include: nocturnal migrationmaximizes day-time feeding opportunities, pro-vides more stable atmospheric conditions formigration, allows migrating birds to take advan-

tage of cooler temperatures to lower heat stressand dehydration, and minimizes predation pres-sure from diurnal raptors (Alerstam 1990, Able2001). Predominantly diurnal migration is rela-tively rare in passerines, having been documentedin only a few families, including Corvidae,

Sturnidae, Hirundinidae, Fringillidae, and someIcteridae (Evans and Rosenberg 2000, Able 2001,Evans and O’Brien 2002).

Detecting the specific identity of nocturnallymigrating birds is largely limited to two tech-

niques: (1) scavenging birds killed during nightmigration at radio towers, lighted buildings, andother human made structures, and (2) identifyingspecies by listening to or recording their flight

calls. Many migratory songbirds produce flightcalls, a primary vocalization given during sus-

tained flight. Flight calls are prevalent amongNorth American passerines, although not all

species produce them. For example, species ofTyrannidae, Laniidae, Vireonidae, Troglodytidae,

and Mimidae are not known to give flight calls butare nocturnal migrants (Evans and O’Brien 2002,

Farnsworth 2005). Passerine flight calls aretypically between two and 10 kHz and ,1 sec

in duration (Ball 1952, Evans and O’Brien 2002).Flight calls, like songs and other calls, are species-

specific, varying in frequency, duration, modula-tion, and pattern among taxa (Farnsworth and

Lovette 2005). Flight calls are theorized tomaintain flock stability (Hamilton 1962) or

spacing by communicating information amongmigrating birds in close proximity to each other

(Thake 1981). Flight calls were first documentedin 1899 when Orin Libby detected over 3,000

flight calls in a single night (Libby 1899).Advances in spectrographic analysis and inexpen-

sive recording devices (Evans 1994, Farnsworth2005) and, especially a well-documented catalog

of flight calls that allows identification of mostspecies (Evans and O’Brien 2002), have made it

possible to identify species and document theirtemporal and spatial nocturnal migration patterns

(Evans and Rosenberg 2000).

Migratory movements of North American spe-

cies or subspecies of fringillids, although occa-sionally detected in pre-dawn hours, have not

previously been documented in night passagemigration (Evans and O’Brien 2002). Both diurnal

and occasional nocturnal passage migration havebeen documented in two European species, Com-

mon Chaffinch (Fringilla coelebs) and EuropeanGreenfinch (Carduelis chloris) (Clement 1999),

and in Greenland and Eurasian subspecies ofCommon Redpoll (Acanthis flammea) (Knox and

Lowther 2000). We document for the first time theapparent nocturnal migration of Pine Siskins

(Spinus pinus), a species normally considered adiurnal migrant but whose flight calls are readily

distinguishable among the fringillid species.

1 32 Vassal Lane, Cambridge, MA 02138, USA.2 Boreal Songbird Initiative, 1904 Third Avenue, Suite

305, Seattle, WA 98101, USA.3 Department of Biology, Bates College, Lewiston, ME

04240, USA.4 Corresponding author;

e-mail: jeffwells@borealbirds.org

SHORT COMMUNICATIONS 161

METHODS

Waterproof pressure-zone microphones were

used to concurrently record nocturnal flight callsfrom 2 to 16 October 2008 at three locations

within 6 km of Gardiner, Maine, USA. Site #1

was at 44u 139 N, 69u 469 W; Site #2 was at 44u139 N, 69u 479 W; and Site #3 was at 44u 169 N,

69u 479 W. Two microphones were within 2 km of

each other and the third was ,6 km distant. Twomicrophones were in suburban neighborhoods with

low level street-light illumination while the third

was on the border of an extensive forested areawith no artificial lighting. All three locations were

within 1 km of the Kennebec River, a major

southward flowing river. Each microphone wasplaced and pointed upwards so that it had an

unobstructed path to the sky. Acoustic XLR cable

connected the microphone to a Rolls MP13 pre-amplifier housed in a nearby building. The signal

was sent from the pre-amplifier into a computer

which automatically activated two simultaneouslyrunning bird flight call detection software pro-

grams (Thrush-r.exe and Tseep-r.exe; both distrib-uted as shareware from www.oldbird.org) at 2000

hrs EST and de-activated the programs by 0600 hrs

EST the next morning (the detector programs atone station at times were allowed to continue

slightly past 0600 hrs EST). Each potential bird

flight call detected by either program was saved asa WAV file with a file name reflecting the date and

time it was detected. All sound files collected were

reviewed aurally and spectrograms inspectedvisually using Glassofire sound analysis and file

sorting software (distributed as shareware from

www.oldbird.org). Non-bird sounds were re-moved and bird sounds were sorted and saved

by date. More detailed spectrographic analysis

and measurements were completed using Ravensound analysis software (available from Cornell

Laboratory of Ornithology, Ithaca, NY, USA).

Flight calls that we considered to be of Pine Siskinsbecause they were identical to the well-known

and described ‘‘Kdeew’’ flight call of the spe-

cies (Sibley 2000), based on our own fieldexperience, were saved and sent to flight call

and bird identification experts William Evans,

Michael O’Brien, and David Sibley for externalreview.

RESULTS

We identified 212 of 2,432 flight calls detected

at all three stations that we considered likely

characteristic of Pine Siskins. Our three expertreviewers independently concurred that 90% ofthe calls were clearly identifiable as Pine Siskinflight calls. We were left with 190 calls that wereconfirmed as those of Pine Siskins after removingcalls for which there was not consensus amongour experts. All flight calls were archived atMacaulay Library of Natural Sounds at CornellLaboratory of Ornithology (catalog numbers140388–140396).

Our stations recorded Pine Siskin flight callsfrom 10 to 16 October 2008 when all threestations were shut down for the season. Calls weredetected as early as 2146 hrs EST and as late as0606 hrs EST (Fig. 1), but detections occurredthroughout the night with calls detected in everyhour between 2300 and 0600 hrs EST thefollowing morning. Approximately 90% of re-corded flight calls were between 0000 and 0500hrs EST, and ,80% of calls were at least 1 hrbefore sunrise (Table 1). One hundred and thirtyof the 190 recorded calls occurred on 15 October2008. Recording stopped on 16 October and thefull extent of migration dates is unknown.

DISCUSSION

Many species of North American finches thoughtto be virtually exclusive diurnal migrants, includingPine Siskin, have been recorded producing flightcalls in the hour before sunrise as they begin theirdiurnal migrations (Evans and O’Brien 2002).Flight calls of Pine Siskins were recorded in ourstudy in significant numbers throughout the nightover multiple nights and multiple locations, sug-gesting these birds were likely undergoing noctur-nal migration. To our knowledge, this is the firstdocumented observation of apparent nocturnalmigration in this species.

The migratory irruptive behavior of Pine Siskinsis apparently induced proximately by a lack of foodresources, primarily conifer seeds (Dawson 1997).Pine Siskins are known to make long-distancemigratory movements biennially on average (Bockand Lepthien 1976, Yunick 1983, Hochachka et al.1999), apparently due to broad scale synchronicityof conifers in their biennial cycle of coneproduction (Pielou 1988). Birds will not show theselong-distance migratory movements when coneproduction is high in a particular region, while inpoor seed production years, large numbers willmove in search of food (Dawson 1997).

Nocturnal migration could be a behavioral traitthat is only expressed by finches under extreme

162 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 123, No. 1, March 2011

conditions of food shortage which induce long-

distance migratory movements similar to those

seen in determinate long-distance migrants (Ho-

chachka et al. 1999). There was an unusually large

migratory irruptive event for Pine Siskins during

the 2008–2009 season, especially in the eastern

United States. The average flock size reported by

Project FeederWatch participants in the eastern

U.S. doubled from the prior year’s migration (7.2

to 15.5), and the number of feeders visited

increased by 31% (D. N. Bonter, pers. comm.).

Data from eBird across ,480 sites in Maine, New

Hampshire, Vermont, and Massachusetts showed

a detectable pulse in the frequency of checklists

reporting Pine Siskins in the second week of

October 2008 from 1.7% in week one to 11.2% in

week two and 7.1% in week three (eBird 2010).

This pulse corresponded with the period when we

detected Pine Siskin night flight calls suggesting

that a broad-scale migratory movement of the

species was underway across New England. The

frequency of 11.2% in the second week of

October 2008 was the highest observed for Pine

Siskins in October since 2001 (eBird 2010).

Another irruptive cardueline finch that occurs

in North America, Common Redpoll, has been

heard migrating nocturnally in Greenland and

Eurasia (Knox and Lowther 2000), but there are

few data on the extent and timing of this behavior.

These and our observations suggest this is a rare

behavior among finches. Future study of nocturnal

migration during irruptive years could help

explain if nocturnal migration is a plastic behavior

induced under conditions that lead to broad scale

FIG. 1. Number of nocturnal flight calls of Pine Siskins detected at three sites near Gardiner, Maine during 10–16

October 2008, by hourly interval (EST). Sunrise occurred at 0551 hrs EST.

TABLE 1. Number of Pine Siskin flight calls detected per night at each of three sites near Gardiner, Maine from 10 to

16 October 2008. Recordings were not made at all sites on all nights, as indicated by ‘‘N/A’’.

Site 10 Oct 11 Oct 12 Oct 13 Oct 14 Oct 15 Oct 16 Oct

1 28 0 0 0 11 80 N/A

2 2 16 3 0 N/A N/A N/A

3 N/A 1 0 0 0 50 4

SHORT COMMUNICATIONS 163

irruptions in contrast to a seemingly determinatemigration strategy as seen in virtually all otherpasserines.

ACKNOWLEDGMENTS

We thank the Tyler and Hynes families for use of their

homes as recording sites. We thank the Biology Department

at Bates College for funding all travel expenses for M. L.

Watson. We also thank W. R. Evans, M. O’Brien, and D. A.

Sibley for reviewing our recorded flight calls.

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