Little Grebe

Of all the grebes in Europe, it is the smallest one that frequently performs nocturnal territorial flights and in so doing, utters a penetrating pik, pik… pik, pi-pi-pe-pe-pe-pe-pe-pe-pe-pe-pe-pe-pe.

On the water, Little Grebes engage in courtship displays with a duet of long tittering trills. Male and female trills are so perfectly synchronised in unison that it is difficult to discern who starts first. In territorial dispute, Little Grebes use a different long trill, this time uttered by only one of the two, usually for defence (cf. Hartley 1937). Besides being slightly lower-pitched, it differs more markedly by having just a single frequency band. Courtship trills by contrast have several harmonics of similar strength, showing in sonagrams as several frequency curves of similar shape, one above the other. It is the territorial trill that Little Grebes also use as NFC in territorial flights, which at some point become indistinguishable from genuine migration flights. Compare the visually confirmed recording of a territorial trill below with nocturnal flight call trills in the identification section.

Little Grebe NFCs have baffled ornithologists for years and a common error is to confuse them with Eurasian Whimbrel Numenius phaeopus. For sure, there are similarities but once learned, it is not difficult to discriminate the two. Actually, the mystery of this NFC was solved over half a century ago by Baron van Lynden (1962) after having heard the call for 28 years without knowing what it actually was.

Little Grebes also have a second NFC, which is briefly mentioned by Baron van Lynden (1956) as well. This is a plaintive wailing whee… whee, quite unlike the trill. In our experience, Little Grebes use a similar series of wails in anxiety or especially when lone birds cannot participate in courtship displays of other pairs. Wailing at water level usually involves long series of whee, whereas the NFC is usually just one or two whee together. Arguably, the NFC whee is derived from the wailing series on the water, and may signify lone birds prospecting for congeners. The following recording illustrates a typical situation in which a series of whee calls are being used by a visually confirmed bird.

pik, pik… pik, pi-pi-pe-pe-pe-pe-pe-pe-pe-pe (territorial trill)

• long rippling trill, descending briefly at the start then levelling out, usually preceded by a variable number of pik notes
• generally has three-part structure: pik, pik… pik, pi-pi-pe-pe-pe-pe-pe-pe-pe-pe
  • 1) variable number of loosely uttered introductory pik calls (may be missing or inaudible)
  • 2) first two (or only the first) pi are of higher pitch than the following pe; the two notes can be highly variable in shape, eg, shaped like a ‘U’, ending with a spike, gradually turning from pik to pe, (example b & c)
  • 3) long and quick series of pe notes; the series as a whole is usually on one pitch, sometimes slightly descending or oscillating up and down
• introductory high-pitched pik notes are a diagnostic feature when present (may be lacking, or, used solely, see below)
• individual pe (or pi) notes are arch-shaped; as in Whimbrel
• median of 13 notes per series (90% range: 10 – 21 notes; n = 50; excl. pik calls), thus more than twice as many as in Whimbrel’s NFC
• maximum frequency of the trill 2.2 kHz (mean; ±0.11 kHz; n = 50), measured without the first two pi notes, which are usually higher pitched, and also excludes the odd lower pitched note in-between
• the territorial trill as a whole can be broken off at any point, but typically at the end of one of the three structural parts, eg, after a few pik notes (see below), after a few pik notes and two pi-pi (e) or after long series of pe notes (most common)
• sometimes, pik or pi notes are also added at the end of the long trill (f)

Effects of recording quality

• At close range, the territorial trill may show harmonics above the main pe-pe-pe-pe-pe-pe-pe-pe trill, giving it a closer resemblance to courtship trills. However, the additional harmonics will never be as prominent as in courtship trills.
• At a distance or in noisy surroundings, the introductory pik notes may not be visible or audible. A few pe notes at the end can also be undetectable due to recording quality, which makes the NFC appear shorter (ie, fewer notes) than it actually is. However, the gradually descending beginning of the trill separates it from Whimbrel’s NFC.

whee… whee (wail or lone call)

• plaintive, wailing whee; completely different structure and timbre to the trills
• gently rising pitch; rarely an almost straight frequency line (example l)
• whimpering quality, due to vibrato: slow and shallow modulation of the frequency
• commonly given in pairs – whee… whee – or single whee (out of 66 calls, 32 were pairs and 26 single; 6 were triple and 2 quadruple)
• two harmonics prominent (appearing as two frequency curves one above the other); sometimes the upper is louder, sometimes the lower
• lower curve starts on average at 1.8 kHz (±0.14 kHz; n = 27) and rises up to max frequency 2.1 kHz (±0.13 kHz; n = 32)
• upper curve starts on average at 3.5 kHz (±0.36 kHz; n = 30) up to max frequency 4.2 kHz (±0.28 kHz; n = 33)
• few calls have a short prefix attached to the curve, which sounds like a crack in the voice (h, k & m)
• prefix has different timbre; mean 1.1 kHz distance between max frequencies of lowest curve and the next one above (±0.08 kHz; n = 5), thus a denser array than the main part whee

Effects of recording quality

• In close recordings more than the two harmonics may appear (n) and it becomes a little more difficult to identify the two prominent ones.
• At a distance or when overlapped with bird songs or noises, only one of the two prominent frequency curves may be visible. Since either the lower or the upper curve can be louder, and therefore one of the two can be invisible in sonagrams, it is easy to be confused about which curve you are looking at.

pik (introductory notes)

• variable high-pitched pik notes are sometimes given without further territorial trill
• shape extremely variable; ranges from slightly arched, or inverted like a shallow ‘u’, or with a foreleg coming from below and a spike at the end (‘hindleg’ going upwards), or sharply uprising with or without an additional spike, etc.
• peak frequency can be anywhere between 2 – 4 kHz (n = 26)
• has a penetrating sound to it; probably because it is uttered loudly (sounds like an ice axe hammering into a solid ice block)
• often uttered three times in a row; a single pik note without any further evidence of another Little Grebe NFC should be identified with special caution

Effects of recording quality

• Distant calls, or calls obscured by background noise, can lose any ‘hindleg’, spike or ‘foreleg’ and, therefore, may appear as a single dot in sonagrams. These calls can only rarely be identified with certainty. A single pik note, especially at a distance can sound confusingly similar to any other man-made noise (eg, a rope banging against a flagpole).

pik, pik… pik, pi-pi-pe-pe-pe-pe-pe-pe-pe-pe-pe-pe-pe

• Eurasian Whimbrel Numenius phaeopus is the main confusion risk. However, Whimbrels 1) never introduce their NFC with high-pitched pik notes; the last of which is often the first of the trill in Little Grebe; 2) Whimbrel’s pi-pi-pi-pi-pi-pi is on average shorter than the territorial trill of Little Grebe (ie, fewer notes: median 6 compared to 13 in Little Grebe); 3) Little Grebe’s territorial trill drops gently in pitch from pi to pe at the beginning of its trill; 4) Whimbrel’s trill averages slightly higher-pitched: the maximum frequency of the single arch notes is marginally lower-pitched in Little Grebe.
• Common Cuckoo Cuculus canorus females have a bubbling advertising trill, also used as a NFC, that is similar to Little Grebe’s territorial trill. Differences in Common Cuckoo included that their NFC 1) typically rises from a lower pitch at the beginning then falls more noticeably over its entire length, whereas Little Grebe’s NFC drops in pitch at the beginning; 2) has a slight but noticeable deceleration in delivery speed of the single notes towards the end; 3) has individual notes where the rising ‘foreleg’ has more energy than the arch at the top, the strongly rising pitch in each note creating the ‘bubbling’ quality; 4) Common Cuckoo’s NFC as a whole is even lower-pitched than Little Grebe’s NFC and often starts very low at c 1.5 kHz.

whee… whee

• Unmistakable. Although Water Rail Rallus aquaticus has remotely similar calls in its repertoire, these are not known to be given in flight or at night.

• anywhere: over towns, forests, deserts, offshore
• strictly nocturnal: no known diurnal flight calls
• can be expected at any hour

We do not know much about the radius of nocturnal territory flights. Therefore, it is reasonable to err on the side of caution when it comes to numbers of migrating individuals per night. Especially in spring and summer it is wise to apply extra caution when a suitable pond or lake exists within one kilometre of your listening post. However, we have recorded Little Grebes over vast spruce forests in mountain ranges (h) where the species is otherwise a rare migrant.

Hartley, P H T 1937. The sexual display of the Little Grebe. British Birds 30: 266–275.

van Lynden, A J H 1956. Wie kent deze roep? Wiek en Sneb 4: 60.

van Lynden, A J H 1962. Dodaars als (hoogvliegende) nachttrekker. Het Vogeljaar 10: 291