At least 10 different categories of contact (flight) calls have been described (58, 6), in addition to those for Cassia Crossbills (12, 13). Cross-fostering experiments in aviaries (58, 175) and field studies of banded juvenile crossbills and their parents (Cassia Crossbill) have revealed that crossbills imitate the contact calls of their parents. However, an adult’s contact call can change over time (176, 24) through the process of call convergence (176, 24) in which birds in a mated pair modify their call structure to match each other. Based on the results of placing individuals of Type 3 and Type 4 in both homotypic and heterotypic pairings in aviaries, Sewall (24) found that adult vocal learning appeared limited so that crossbills modify their calls to match homotypic mates but are unlikely to change “call type” to match those of a different call type. However, Keenan and Benkman (176) found one female Type 2 changed her contact call between years from Type 2 to that of a Type 9 (Cassia Crossbill) to match her mate’s call by the second year. Two more cases of Type 2 individuals switching their calls between years to match Cassia Crossbill contact calls have been detected, as have three cases of Cassia Crossbills switching their calls to match Type 2 calls, whereas there has been no documented call switching between Type 5 and Cassia Crossbill (out of 846 banded individuals recorded over more than one year; C. Porter and CWB, unpublished data). These results were found in an area where Types 2 and 5 are sympatric with the Cassia Crossbill. Call matching is not found for all pairs in the wild (e.g., ~two-thirds of Cassia Crossbill pairs call matched; 176), but appears to occur between pairs that bred together previously (see Groth  for striking call matching of nonbreeding pairs). If a pair is sufficiently compatible to, for example, remain paired for multiple mating attempts, call matching ensues in some cases even when involving the rare mixed pair (176). Forced pairings of a small number of individuals in captivity (e.g., Sewall ) might not accurately reflect what occurs in the wild under differing environmental and social conditions. Nevertheless, call switching appears rare (< 1% of individuals) because crossbills are more likely to respond to, and associate with, individuals giving contact calls of their own call type (23, 24, 22), although such a preference possibly declines when presented with only individuals of one other call type (e.g., 177). Thus, contact calls can be considered a reliable indicator of shared ancestry (176, 24) and the rarity of observed mixed pairs (11, 49) is because of assortative pairing rather than call imitation preventing the detection of mixed pairs
Like most oscines, crossbills learn contact calls during the nestling stage (first week; 175) and perhaps the fledgling stage (3, 175; see also 176). Cross-fostering and playback experiments show that nestlings do not have a predisposition to respond to or learn the contact calls of their biological parents over those of other call types, but rather social experience is critical to imitative learning of vocalizations (3, 175). Fledglings follow foraging parents, making calls that appear to vary little among the types (see “Chitoo Calls” below), but by time of independence or about 60 days post-hatch, contact calls have stabilized and are similar to those of their parents (3, 175).
Song. Sings in flight or perched on treetops or near nest; stereotyped shorter song variously described as pit-pit, tor-r-ree, tor-r-ree, or even whit-whit, zzzzt, zzzzt, zzzzt (132, 149). Each male has several variations (Figure 17), and there is variation among types (58, 12, 6). Long social song is often slightly softer than their stereotyped song, and it takes on a very conversational pattern consisting of several fast phrases strung together over sometimes many minutes.
The tonal quality of the songs (i.e., especially the stereotyped song) appears to take on the quality of sound similar to described call type. There appear to be diagnostic patterns to songs of some of the types: Type 1 seems to incorporate many more whistled and trilling phrases to its song (MAY) in addition to sharp sounding call notes; Type 10 gives many buzzy sounds in their songs phrases (6) and the song appears thin much like their “whit-whit” contact calls; Type 3 song phrases often contain a distinctive upward modulated ascending note (6) and their song sounds squeaky, scratchy and weak like their contact call; Type 2 strings together a jumble of contact-like call notes and their songs sounds powerful as one would think would be given from a large-billed bird. Although some phrases seem distinct to call type, there is much overlap as well. Type 5 appears to give song phrases more consistent than other types from year to year. More study is needed.
Flight songs are accompanied by exaggerated, slow wing-beats. Although both sexes sing, females sing less often and less loudly than males (58). Females increase song rate in response to testosterone implants (142).
Contact (flight) Calls. See Figure 4. Contact calls (i.e., flight calls) are the best known of all calls. Described variously as tik-tik-tik, chip-chip-chip, or jit-jit-jit. The tik notes are separated by about 250 ms (milliseconds), triplets separated by about 800 ms. Excited birds give as many as 7 or 8 chips in continuous bout. Some variants are easily distinguished by ear; others are subtler. Contact calls are the basis for assortative flocking in the wild (22; see Systematics: Geographic Variation and Subspecies), with mixed flocks encountered uncommonly except for in years where there’s significant movement of several crossbill call types. Contact calls are learned with offspring imitating their parents (58, 176, 175), as in some other cardueline finches (178, 179).
The contact calls of some call types sound more similar to other call types such as Type 1 and Type 2; occasional "kinked" Type 2 (e.g., see below for more on "kinked" Type 2) and Type 3; and types 4, 6, 7, and 10 all share similarities in contact call structure as well (see spectrograms for the shape and look of the contact call structure). Types 1, 5, 9 (Cassia Crossbill), 11, and occasionally 2 are polyphonic (see below for more on polyphony). In the detailed description of call types below, the more similar-sounding contact calls have been grouped together so one can start to breakdown the differences across the types.
Types 1 and 2 (and Cassia Crossbill): Type 1 contact calls sound much like the choowp-choowp-choowp of Type 2. The spectrograms for both Type 1 and Type 2 are dominated by a downward component, although confirming Type 1 and Type 2 contact calls requires audiospectrographic analysis. Type 1 spectrogram starts with an initial upward component in nearly all cases, and the downward part descends more quickly than in Type 2 (duration of the Type 1 call is < 0.04 s nearly all the time). Overall, Type 1 contact calls are more attenuated, dryer and sharper than the slightly ringing sounding contact calls of Type 2, and sound like chewt-chewt-chewt (9). Types 1 and 2 can have secondary ending components, but they are more common and prominent in Type 1. Type 2 usually produce a "kinked" contact call in the West and an “unkinked” call in the East (9). Type 1 gives contact calls that are polyphonic, but not nearly as polyphonic as that of Type 5. Cassia Crossbill (Type 9) dip-dip-dip contact calls are also polyphonic, and will start with an initial upward component, therefore looking a bit like the Type 1 and Type 2 spectrograms. However, the modulation of the contact call is consistently given in a lower frequency domain (below 4.0 kHz) than in types 1 and 2. Overall, the Cassia Crossbill contact call sounds much lower and there’s a flat harsh quality to them.
Types 3 and 5: The contact call tik-tik-tik or kyip-kyip-kyip of Type 3 is weaker, squeakier, and flat sounding than the other call types (9). The Type 3 spectrogram has a zig-zag appearance and begins with a downward component, followed by a short upward component connected to a second downward component. As noted above, occasionally "kinked" Type 2 can also sound and look similar to Type 3 in that there’s a zig-zag appearance to the spectrogram, but "kinked" Type 2 is always given in a lower frequency domain with less range.
The Type 5 contact call is often described as a twangy or metallic clip-clip-clip. The Type 5 spectrogram has 2 elements that drop in frequency, but these elements are given in slightly different frequency domains. The second element begins almost immediately after the first element, such that the elements connect or nearly connect, thus forming the letter "n" or "h" on the spectrogram. Both elements are modulated differently over the same time span indicating that each is produced by a different side of the syrinx, thus producing sound polyphonically similar to Catharus thrushes (3, 180).
Types 4 and 6 (and Type 8 L. c. percna): Type 4 has a bouncy, almost musical plick-plick-plick or pwit-pwit-pwit contact call that is among the most distinctive, even when compared to Type 10 (it was recently split from Type 10; see Irwin ). The spectrogram is dominated by a "down up" component with the rising component looking very similar to the Type 10 contact call. Overall, the contact call spectrogram resembles the letter "V".
The cheep-cheep-cheep contact calls of Type 6 are tonal and slightly ringing with a downward-modulated frequency and an abrupt terminal rising component (3). Type 6 contact call is actually a closer match in both sound and spectrogram to that of Type 4, but the latter almost always has a deeper V-shape in frequency. Type 4’s flatter pwit-pwit-pwit sound and the typically lower pitch separate it from Type 6’s more ringing cheep-cheep-cheep sound. The gentler, U-shape contact call of Type 6 reaches a minimum frequency of 2–3 kHz, which is approximately the same minimum frequency as Type 4. Not much is known about Type 6—by ear it sounds similar to Type 8 of Newfoundland, although the spectrograms are different. The contact call of Type 6 is much less modulated than the cheet-cheet-cheet, m-shaped contact call of Type 8 (9).
Types 7 and 10: The spectrogram of Type 7 is often described as an upsweep followed by a downsweep or "tail." Type 7 can sometimes sound and appear in spectrograms similar to Type 10, but more study is needed (9). The main frequency of sound (jit-jit-jit) can be described as sometimes having a short initial fall, or more commonly just having a longer rise followed by a shorter fall (the "tail”). The U-shaped calls previously identified as Type 7, appear to be a variant of “kinked” Type 2, whereas Groth’s jM498 (3) is a perfect match to eastern birds currently listed as Type 10. More recordings are needed. Measurements of a handful of birds recorded in Michigan showing spectrograms similar to Type 10/4/7 appear to be a noticeably larger-billed bird than Type 10s in the West (J. Cornelius, personal communication).
The contact call of Type 10 is a fairly distinctive call type, a very thin, slightly weak, non-musical whit-whit-whit, whereas the jit-jit-jit sound of Type 7 has a notably harsher sounding edge to it (9). The whit-whit-whit sounds much like the “whit” call of a Least Flycatcher (Empidonax minimus) or Dusky Flycatcher (E. oberholseri). The spectrogram is dominated by an upward component and can often look like a "check-mark".
Type 11 L. c. mesamericana: Type 11 give a flat, polyphonic contact call that can sound similar to the Cassia Crossbill or some lower-frequency variants of Type 5. It could be represented by drip-drip-drip, and sounds very different than the slightly ringing quality heard in Type 6, with which it overlaps in distribution (9).
Excitement (“toop”) Calls. Given at times of stress such as in response to competing mates during nesting, aggression among flock mates (3), or when a raptor is nearby (T. Hahn, personal communication); described by Nethersole-Thompson (149) for Scottish Crossbill as “deep toops.” Wild birds quickly approach playbacks of excitement calls, themselves often tooping (60, 181). Excitement calls can also often be used to identify birds to call type (3), and the combination of excitement and contact calls are used in Europe to distinguish call (vocal) types (60). Toop and alarm calls are on the same continuum, and therefore alarm calls are often referred to as toop calls (N. Pieplow, personal communication).
Overall, excitement and alarm calls overlap considerably among the different North American call types. Type 1 excitement calls are simple in structure, are slightly modulated where the frequency rises moderately then falls briefly, and often have chevron-shaped (3) elements that can stack upwards, and as a result look similar to Type 2 alarm calls. Type 1 excitement calls can also sound like those given by types 2 and "eastern Type 10". Type 2 excitement calls are more complex usually dropping in frequency before rising and falling again; but overall have a rising inflection. Type 3 excitement calls have 2 prominent components. One is a low frequency element similar to those of Type 4, while the other is produced simultaneously at a high frequency that rises then slowly falls; these 2 modulation patterns together produce a dissonance. The nasal sounding Type 3 excitement call is quite distinctive, but the spectrogram is similar to those of Type 2. Excitement calls of types 2, 4, and 10 are similar and hard to discern from each other with reliability. Many Type 2 and Type 4 excitement calls have harmonics. Harmonics were seldom recorded for Type 10 excitement calls (6). Type 5 excitement calls are short in duration, tonal, and share similarities with Type 3 alarm calls. Type 5 excitement calls appear to have separate elements layered at different frequencies. The same layering found in Type 5 excitement calls can also be found in those of Type 6.
Alarm Calls. Alarm and excitement calls overlap considerably among the different North American call types. Birds seem more agitated when giving alarm calls than when giving excitement calls, and sound like tut-tut (CSA), ooks-ooks (149), or tuck, tuck, tuck (43). Made in response to flying predators or to predators near nest (142). Alarm calls appear to be just a heightened version of excitement calls. All the call types have elements in their alarm calls that are layered like those in the excitement calls of many call types. Softer more consistently given alarm calls appear to be given when a danger is more imminent like when an accipiter or merlin is present (T. Hahn, personal communication).
Distress Calls. Harsh screams, made when captured in nets or, presumably, by predators. Can grade into alarm calls (3).
Chitter Calls. Are soft conversational calls that are named after their sound. Used in foraging flocks with birds in close proximity, and when wild birds approach decoys or approach water to drink. Given while drinking in exposed locations, suggesting a low level of stress (6). Highly variable structure suggests that Chitter Ccalls can be subtly graded for variety of messages.
Courtship and Copulation Calls. Highly variable. Grade into chitter and contact calls.
Threat or Aggression Calls. High-pitched calls often associated with head-forward Threat Display (illustrated in Tordoff ) used before or in lieu of fighting. Threat Calls and fighting induce Excitement Calls in captive individuals (142).
Chitoo Calls. Juveniles give “chitoo” calls repeatedly when following parents, with greater frequency when begging for food (142). There seems to be little, if any, variation in “chitoo” calls among call types (MAY).
Daily Pattern of Vocalizing
Often sing at first light, but much of the morning is spent foraging until mid to late morning before singing resumes. Singing can last well into the afternoon, particularly with presumed unmated males.
Places of Vocalizing
Males sing in flight, from treetops, even near nest, though more quietly when near nest (171). Females presumably sing from the same locations as males.
Repertoire and Delivery of Songs
Birds appear to give 2 very different song types: a fast, long plastic “social song” that sounds very conversational, given when in flocks that are not associated with breeding, and a much more stereotyped “shorter song” consisting of distinctive repetitive song strophes (i.e., phrases) given once birds have started to form small breeding groups or pairs (MAY). Social songs can be given at nearly any time of the year, including migration, but do seem to increase in frequency and duration with the approach of the winter nesting period in January and in spring when day length is increasing as a precursor to summer nesting (MAY). More work is needed to determine whether there are additional behavioral contexts for long social songs and short stereotyped songs.