Tree Pipit

Tree Pipit NFCs are similar to their daytime flight calls but may nevertheless sound unfamiliar. The pitch at night may be slightly lower than you are used to, there are many two-note calls, and some have only a hint of the familiar buzzy timbre. When we are out birding in the day, it is the highest-pitched, most buzzy and ‘explosive’ calls that attract our attention, the kind that startle us when a hidden Tree Pipit unexpectedly takes off just ahead of us. At night we hear a different selection from the variations present in Tree Pipit’s repertoire.

One flight call that migrants use during the day is a very short, descending sip lacking any fine modulations, which you may know as Tree Pipit’s ‘alarm call’. In over a decade, however, we have not recorded it ourselves at night with certainty. While such an NFC may yet exist, you should certainly consider other short, similarly-pitched NFCs such as the the tsrp of an Ortolan Emberiza hortulana or the wit of a Pied Flycatcher Ficedula hypoleuca.

Tree Pipits clearly illustrate a feature that is typical for the genus Anthus. While most calls show a single band in sonagrams, at closer range a weak second band appears at exactly half of its frequency. The lower, weaker band is the fundamental frequency or first harmonic, and the stronger band is the second harmonic. All pipits show a strong second harmonic, and in most species, it is stronger than the fundamental. If you are struggling to identify a passerine call showing this feature, it is more than likely to be a pipit.

spihz calls

• high-pitched, usually buzzing, slightly descending call
• often doubled; roughly 57% single-note and 38% double-note calls; triple calls and especially quadruple or longer are rare (n = 183)
• asymmetrical arch with greater part descending; descent may be straight (d) or more curved (e); minority show more symmetrical arch (a, h); few have flat (a) or slightly rising top (m)
• modulations create buzzy timbre; 68% have fine type 1 modulations measuring 5.7 – 7.6 ms (90% range; median 6.7 ms; n = 125); most other calls have more untidy type 2 modulations measuring a multiple of this, eg, 11.4 – 15 ms (g, h, k); type 1 modulations sometimes nestled within type 2 modulations (secondary modulations)
• closer calls appear two-banded; fundamental at exactly half the frequency of the dominant band (a, c, e – h); usually weak but occasionally stronger (e)
• main energy in 5.5 – 6.2 kHz range; total range for dominant second harmonic 3.1 – 7.5 kHz from bottom of ‘legs’ to highest modulation (mean minimum 4.1 kHz; mean maximum 6.5 kHz; n = 180)
• duration of first note 95 – 183 ms (90% range; median 137 ms; n = 183); second note shorter, (median 99 ms; n = 66); third note shorter still (median 86 ms; n = 9)
• calls far-carrying; long sequences possible from a single individual

Effects of recording quality

• Fundamental only appears in calls recorded at close range, when stronger giving a slightly ‘thicker’ timbre to the calls.
• ‘Forelegs’ and ‘hindlegs’ appear shorter in more poorly-recorded calls.
• Type 1 modulations easily blurred when echoes present.

• Redwing Turdus iliacus has NFCs that are high-pitched, buzzing and descend in pitch. However, they are twice as long and roughly 1 kHz higher. The modulations are slightly shorter than in Tree Pipit, the call has no ‘forelegs’ or ‘hindlegs’ and the descent is usually straight or has a concave curve.
• European Pied Flycatcher Ficedula hypoleuca has NFCs that are similar in pitch, length and overall curve. Two bands typically just over 1 kHz apart easily exclude Tree Pipit, but one band may be lacking in distant calls. Pied Flycatcher has deepest modulations right at the start; Tree Pipit just after the start or in the middle.
• Red-throated Pipit Anthus cervinus NFCs also frequently has a descending series of successively shorter notes. However, each note usually has a much more pronounced peak near the start, followed by a concave, not arched, descent. Only slower modulations occur (none as fast as Tree Pipit’s type 1). A striking difference is the big drop in pitch from the first to any subsequent notes; in this regard, Red-throated is to Tree Pipit what Redshank is to Common Greenshank.

• anywhere: over towns, forests, mountains, offshore
• nocturnal and diurnal: uses same flight calls day and night
• can be expected at any hour: a bias of activity towards second half of night

As a vagrant, Olive-backed Pipit A hodgsoni will appear in this guide at a later stage and at present we have few positively identified NFCs to study. Many readers will already know the excellent comparison of daytime flight calls by Ralph Martin (2013). Caution is needed before applying the same criteria to NFCs. Many of the birds in the recordings used by Ralph will have been recorded in situations where they were more excited (and higher-pitched) than migrants at night. At present we simply suggest that Olive-backed Pipit is worth considering, but not assuming, for any ‘Tree Pipit’ recorded particularly late in the season. We would be interested to hear any strong candidates.

Martin, R 2013. Identification of Olive-backed and Tree Pipit by call. Avesrares blog.