Pine Siskins, an irruptive finch whose populations and migrations depend on pine cone crop, are a common fixture across Vermont, especially in some winters. While not traditionally considered a nocturnal migrant (Evans and O'Brien 2002), they have been known to migrate at night (Watson, Wells and Bavis 2011, Mandelbaum 2020).
Pine Siskins give a variety of flight calls: a zree or waaaee call, somewhat like their rising idiosyncratic zhree zipper calls; a Goldfinch-esque flight call, described as jirp jirp jirp or chu-tu-tu-tu; a zweew call, similar to the zree; chit calls; and klee-you calls (Evans and O'Brien 2002, Pieplow 2017). Choosing which call is most relevant for a given recording can be difficult, as can be disambiguating calls from other species.
Determination of exact number [of calls] is difficult because of apparent variation in phonetic rendition among observers. Like other carduelines, frequently gives flight calls. Calls of this species are generally characterized in terms such as “rasping” and “throaty” (Dawson 1923)...
Unfortunately, this species' repertoire is extremely similar to both Redpolls and both Goldfinches. I struggled to find a single way of telling them apart reliably by looking at the spectrogram, for any of the published records of these calls. The klee-you described by Evans and O'Brien (2002) appears to be idiosyncratic, but the zree calls can be easily confused, and the jirp jirp flight calls are not plastic, while similar Redpoll calls are extremely plastic, making sure identification difficult.
For this species, I would strongly encourage discretion for identifying the species, and reliance upon both finch irruption charts during the recording time (how likely is it that it could be a Hoary Redpoll? Luckily, most likely not very, especially in Vermont) and close listening to the recording itself, judging the raspy nature of the Pine Siskin. Many calls may be best left unidentified.
Watson, Wells and Bavis (2011) first logged recording NFCs for Pine Siskins, using only the kdeew call:
Flight calls ... we considered to be of Pine Siskins ... were identical to the well-known and described Kdeew flight call of the species (Sibley 2000).
Pieplow (2017) describes several calls, given diurnally:
Zree - Rising, polyphonic. Zweew - Overslurred, slightly burry. Both all year. Zree possible in alarm; Zweew, possibly a variant of Zree, often with Flight Call.
And:
Flight Call: Jirp jirp jirp. All year, in contact and flight. Only slightly variable. Lower, less musical than Lesser Goldfinch Flight Call. ... Polyphonic, slightly noisy notes in series.
Sibley (2016) notes briefly:
Common call a rogh, rising buzz zhreeeeee. Flight call a high, sharp kdeew and a dull bid bid.
Evans and O'Brien (2002) give four possible NFC calls, but note that Pine Siskins are not known to give flight calls nocturnally. Research on this may have changed this view in the past two decades. The calls given are:
A quick, harsh chu-tu-tu-tu, a strident, emphatic klee-you, and a rising, nasal waaaee are the most common flight calls. Also gives a short chit. Occasionally given in flight, but more typically from a treetop, is a long, rising, buzzy zreeeeeeee.
Sanders (2013) notes a "distinctive low double peak", and shows a spectrogram of a Pine Siskin, which doesn't match any other records I could find.
Dunne (2006) notes:
Call notes include a rising eeeh? (like a goldfinch), a Chee (a cross between a chip and a snarl), and a more buzzy and ascending zzzzeh! (the celebrated "zipper" call). Also gives a chew ch ch ch reeeh? in flight. Many of the sounds are similar to a goldfinch but harsher and squeakier.
These are eyeballed from Pieplow (2017).
These are eyeballed from Pieplow (2017). These calls are given in groups of 3-5. "First 1-2 notes often different" (Pieplow 2017).
Evans and O'Brien (2002) show a slight dip in the central bands, almost Canada Warbler-esque.
This is a fairly good zree example, from the main eBird page. This is presumably the disjointed song mentioned by Pieplow (2017), which may also be the klee-you of Evans and O'Brien (2002). Here is a good example of the flight call.
Other calls:
This section may not be helpful. The idea is to make it easier to rule out other species more easily without going through the whole list, which may not be possible.
The following species were noted as being similar by the cited experts. Any notes underneath the species can be used to rule out the other species for particular calls.
When describing this call in comments on an NFC checklist, try and add as many salient notes as possible and refer to this page for justification. If there are any species which seem similar, please get in touch so we can add them here. The intent here is to have a full list of differences for each possible similar call.
All of the Pine Siskin and their associates calls are confusing to track down and compare due to phonetic differences. I have done my best.
The Zree call, a rising polyphonic call, is one of the most characteristic calls of this species, but easily confused with some calls from other birds. Dawson (2020) notes:
A grating call with rising inflection is one of the most familiar sounds produced by Pine Siskins. This “watch-winding” note— zree-e-e-e-e-eet, zwee-e-eeet, shr-reet, sooeet, or possibly a husky chee-ee, depending on author—may also serve as flight call or be uttered before or after completion of flight. This call, also described as züm or zzeem, is always accompanied (presumably in perching individuals) by the display of hidden yellow markings in the wings and tail, according to Dawson (Dawson 1923).
This call is described as being similar to:
The Songlike call of the Brewer's Blackbird which most resembles a zree is noted as having an "odd whiny quality" and a "polyphonic upslur". The call shown in Pieplow (2017) has only a handful of bands, and looks much less turbulent than the Pine Siskin zree. It is unclear when this call would be given, as the more detailed page in Martin (2020) lacks the same phonetic representation as Pieplow (2017) (a rather annoyingly common problem for this species).
This bird is a rare vagrant to Vermont, and it seems unlikely this call would be given or used during NFCs. Evans and O'Brien (2002) give "an abrupt, dry, wooden tjek" as the main NFC call, which means that diurnal similarity notwithstanding, this call and bird can probably be excluded from the list of similar suspects.
The spectrograms in Pieplow (2017) look rather similar to the Pine Siskin. However, the bands all appear to rise together, and it is generally only 300mS in length, as opposed to the Siskin's 500mS. The band as well has a slight bump in the first 50mS or so, where it almost has a downturn effect. Looking at the spectrogram should be enough to disambiguate this species.
Evans and O'Brien (2002)'s call has the same feature, for their duraaai call.
Of course, if the zree is simply a poor variant of the more common zhree zipper call, than there may be intergrades between zree and zhree which appear to be similar to Redpolls. I don't have evidence to back any of this conjecture up.
The Hoary Redpoll looks similar to the Common Redpoll; however, the bands are somewhat more irregular, although still rising and rarely crossing (if ever). The same bump as in the Common Redpoll is notable in the first 30mS. (Pieplow 2017)
However, the draaai call shown in Evans and O'Brien (2002), from Gunn (1958), although noted as "fairly atypical", is much more erratic, with crossing bands, and looks, to me, almost indistinguishable from a Siskin. It still has the slight bump in the beginning, which is not typical of the Pine Siskin. Evans and O'Brien (2002) note:
Draaai call distinctive. It is more pure-toned and more evenly rising than Common's duraaai, without the complex dip at the beginning.
Pieplow considers that the Zree is similar to the Pine Siskin, but notes that the Zree is "high, clear, long" for the American Goldfinch, but "Medium-high, fairly long" for the Pine Siskin. Outside of specific measurements, these relative statements have little meaning. (The Lesser Goldfinch and House Finch are "medium-low, long" and "medium-low, short, almost a Zreet", respectively.) Dawson quotes Godfrey in saying that the call of the Pine Siskin is:
“harsher than similar calls of redpolls” and “huskier and more buzzy than the song of the American Goldfinch, which it resembles somewhat” (Godfrey 1986: 570).
Here, we assume they mean the zree call. It seems unlikely that the song would be given during nocturnal or redetermined migration.
Evans and O'Brien (2002) note that "Wuwuiii call particularly similar to redpolls and Pine Siskin but higher and more wavering."
Looking directly at the spectrograms (specifically, those in Pieplow 2017), it is difficult to see a clear differentiation. The American Goldfinch has less formants (or bands), and they appear to be more unidirectionally sloping upwards, while the Pine Siskin's tend to go every which way, and there are slightly more. However, this may be an artefact of the recordings used, and will certainly be difficult to tell from a poor recording of a Zree, as often occur in NFCs, when the bird may be far away or the climate may not be conducive for sound propagation. Length appears identical, and both appear to range from around 2kHz to 10kHz (and perhaps higher, as 10kHz isn't necessarily the cutoff for passerine calls).
Listening, here and if possible, may be the best way to tell the husky or buzzy call of the Siskin from the Goldfinch. However, the American Goldfinch zree is noted as being "in alarm," while, for the Pine Siskin, this is noted as "possible", and elsewhere it is noted as being part of a display call, where the yellow feathers are shown (Dawson 2020). Thus, an NFC that has a Zree call in it may more likely be a Siskin, as their calls may be more plastic.
Pine Siskins are possibly part of a superspecies with American Goldfinches, systematically (Dawson 2020, quoting Am. Ornithol. Union 1998), so confusion here could perhaps be excused. For this particular call, discretion is obviously advised, and may be the better part of the valorous identification.
The jirp flight calls are grouped by Pieplow (2017) with all of the other finches, which includes Red Crossbill, Lesser and American Goldfinch, Olive-sided Flycatcher, both Redpolls, and White-Winged Crossbills. Knowing whether a call is a jirp or a jit is difficult in the field. For this call, listening to the sound itself may again be the best diagnostic, as opposed to using the spectrogram. For the jirp calls, Pieplow (2017) lists the Redpolls as being similar, while also noting explicitly that it is "lower, less musical than Lesser Goldfinch Flight Call."
This call is probably the chu-tu-tu-tu call of Evans and O'Brien (2002).
Both the Common and Hoary Redpoll are noted as having calls that are "hugely variable" by Pieplow (2017). Given the spectrograms in Pieplow (2017) and Evans and O'Brien (2002), I can't think of a reliable way to disambiguate these by sight. Discretion is again advised.
The zweew call, described as "like a seminasal Weew ... but polyphonic", could be given by any of five species: however, only PISI is noted as being rather high, clear. The other four species - Black-headed Grosbeak, House Finch, House Sparrow, and Eurasian Tree Sparrow, are "lower, slightly harsher". On the spectrogram, the last three are similar in range of frequencies, although they are somewhat burrier in construction - meaning, having less clear bands, and more frication throughout the call.
It is unclear if this call is referenced by others, again due to differences in phonetic representation of bird calls.
No listed confounding calls from other species. Possibly the Zweew call of Pieplow (2017).
No listed confounding calls from other species. Rarer call.