SHORT COMMUNICATIONS 
161 
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. 
ABSTRACT—Nocturnal migration is a common 
strategy among North American passerines. Birds of the 
Fringillidae have typically been labeled as predominately 
diurnal migrants. We used pressure-zone microphones 
and automated sound detection software to record flight 
calls of noctumally migrating birds from 2 to 16 October 
2008 from 2000 to 0600 hrs EST at three locations near 
Gardiner, Maine. We detected and recorded 190 Pine 
Siskin (Spinus pirns) flight calls from throughout the 
night at three separate locations. This is the first published 
documentation of apparent nocturnal migration in this 
species. Nocturnal migration may be a facultative 
migration strategy in the Fringillidae that occurs only in 
years in which large irruptive movements occur as for 
Pine 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 nocturnal 
migration is more common than diurnal migration 
among passerines include: nocturnal migration 
maximizes day-time feeding opportunities, pro¬ 
vides more stable atmospheric conditions for 
migration, allows migrating birds to take advan¬ 
tage of cooler temperatures to lower heat stress 
and dehydration, and minimizes predation pres¬ 
sure from diurnal raptors (Alerstam 1990, Able 
2001). Predominantly diurnal migration is rela¬ 
tively rare in passerines, having been documented 
in only a few families, including Corvidae, 
Stumidae, Hirundinidae, Fringillidae, and some 
Icteridae (Evans and Rosenberg 2000, Able 2001, 
Evans and O’Brien 2002). 
Detecting the specific identity of noctumally 
migrating birds is largely limited to two tech¬ 
niques: (1) scavenging birds killed during night 
migration at radio towers, lighted buildings, and 
other human made structures, and (2) identifying 
species by listening to or recording their flight 
'32 Vassal Lane, Cambridge, MA 02138, USA. 
"Boreal Songbird Initiative, 1904 Third Avenue, Suite 
305, Seattle, WA 98101, USA. 
? Department of Biology, Bates College, Lewiston, ME 
04240, USA. 
4 Corresponding author; 
e-mail: jeffwells@borealbirds.org 
Wells , 2 ’ 4 and Ryan W. Bavis 3 
calls. Many migratory songbirds produce flight 
calls, a primary vocalization given during sus¬ 
tained flight. Flight calls are prevalent among 
North American passerines, although not all 
species produce them. For example, species of 
Tyrannidae, Laniidae, Vireonidae, Troglodytidae, 
and Mimidae are not known to give flight calls but 
are nocturnal migrants (Evans and O'Brien 2002, 
Farnsworth 2005). Passerine flight calls are 
typically 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 to 
maintain flock stability (Hamilton 1962) or 
spacing by communicating information among 
migrating birds in close proximity to each other 
(Thake 1981). Flight calls were first documented 
in 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, Farnsworth 
2005) and, especially a well-documented catalog 
of flight calls that allows identification of most 
species (Evans and O’Brien 2002), have made it 
possible to identify species and document their 
temporal 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 passage 
migration (Evans and O’Brien 2002). Both diurnal 
and occasional nocturnal passage migration have 
been documented in two European species, Com¬ 
mon Chaffinch (Fringilla coelebs) and European 
Greenfinch (Carduelis chloris) (Clement 1999), 
and in Greenland and Eurasian subspecies of 
Common Redpoll (Acanthis flammed) (Knox and 
Lowther 2000). We document for the first time the 
apparent nocturnal migration of Pine Siskins 
{Spinus pirns), a species normally considered a 
diurnal migrant but whose flight calls are readily 
distinguishable among the fringillid species. 
