A Boyd’s Shearwater in a Barolo colony
Introduction
As a part of my work monitoring Barolo Shearwater distribution and abundance on the Canary Islands, we are deploying several automated recording systems (ARS) to cover all the historical colonies of the species and some potential undiscovered places. Each device is set up to record every night during the species’ vocal activity peak (from 5–7a.m.), and the battery therefore can last for up to 2 months. The amount of data is huge and the analysis can be exhausting. However, many weeks of routinely scanning through Barolo vocalisations have given me much experience with the species’ repertoire to that point that a strange-sounding individual stood out. The recording came from a well-known Barolo Shearwater colony in southern La Gomera – a stronghold for this endangered species – at a time when there was moderate Barolo Shearwater activity around the colony. Spectrograms analysed finally confirmed the identification of this bird as a male Boyd’s Shearwater Puffinus boydi (see below).
Figure 1. Boyd's Shearwater Puffinus boydi off Raso, Cape Verde. April 2019. © Guillermo Rodríguez.
The in-field identification of Barolo and Boyd’s Shearwaters has recently been pushed forward in an excellent paper by Flood & van der Vliet, though there is still limited audio material available. Hence, although the vocalisation recorded on La Gomera is noticeably different from the accompanying Barolos, describing what causes these differences is of interest. Of course, my sample is limited to this one individual and the species might show some variation, but it seems probable that at least birds like this one can be safely identified by voice alone in a vagrancy context. Indeed, a recording such as this one may prove less problematic to accept in some cases than, for example, a seawatching record.
Background
Previous records of Boyd’s Shearwaters off the Canary Is.
Right since Boyd’s Shearwater was elevated to species status and some clues on its identification started to emerge, the first evidence of the species’ presence off the Canary Islands began to emerge. Geolocators deployed by Zuzana Zajková and colleagues on birds breeding in Cape Verde showed that Boyd’s Shearwaters occurs regularly off the Canaries, especially during November and December, when a pre-laying exodus takes place (Zajková, et al. 2017). However, both Boyd’s and Barolo Shearwaters are shy species, usually fleeing from boats and foraging in poor areas, far from seabird concentrations, which might so far have obscured the real status of Boyd’s in northern Macaronesia.
There is currently only one record of the species accepted in Spain – a bird seen and photographed by myself from a ferry between Tenerife and La Gomera in December 2012 – but some evidences gathered during the last decade seem to indicate it could regularly occur on the Canary Is (Gil-Velasco, 2013; Zajková, et al. 2017).
Initially identified by myself as a Boyd’s/Audubon’s Shearwater, the Spanish Rarities Committee finally felt the bird was acceptable as Boyd’s based on likelihood and that the aforementioned tracking data showed some tagged Boyd’s to be moving through the Canaries during that exact time period (Copete, et al. 2015). Following a record from Denmark, we now know that Audubon’s Shearwater can also occur in this side of the Atlantic (Flood, et al. 2020); but there is still a much higher probability of the Canarian bird being a Boyd’s. The full account of this bird can be read here.
Figure 2. Boyd’s Shearwater Puffinus boydi. Ferry crossing from Tenerife to La Gomera, December 10th 2012. © Marcel Gil-Velasco
The next evidence of occurrence concerned a singing male at Timanfaya, Lanzarote, on December 20th 2017, recorded in a Barolo Shearwater colony during the first season of the ongoing long-term monitoring programs. However, only 2 calls were detected, both on the same night and both of a much poorer quality than the recordings presented here, and in the end I did not submitt the record to the rarities committee.
Barolo Shearwater sound repertoire
Since Barolo Shearwater isn’t a species most birders would be familiar with, I thought it was worth to include here a recording of intense courtship activity at another colony in South La Gomera, together with some spectrograms depicting different types of song, most-likely delivered by different individuals. It gives a pretty good idea of the species repertoire and I hope even those with less experience with this complex might be able to hear the differences with the presumed Boyd’s.
Figure 4. Different examples of male Barolo Shearwater Puffinus baroli spectrograms. All the exhaled phases are composed by 3 to 6 peaks, with a tendency to increase the number of peaks as the song goes on. The peaks are similar, although some birds can sometimes produce sharper modulations leading to more pointed peaks, as in C). Peaks can be connected (D) or discrete (C), but most individuals produce both types (A & B).
The inhaled note tends to be arched, without a flat topping, and readily follows the last exhaled note. A) and D) show how flat it can get, while B produced a combination of quite flat and arched notes and C) very arched notes..
In addition, the overall frequency stays the same along the entire song.
Note also the short distance to the first visible harmonic, what makes them sound harsher (particularly visible in the last 2 phrases of C), almost female-like!).
A) Male Barolo Shearwater Puffinus baroli. Montaña Clara, Canary Islands, December 2019. ©Cory’s
B) Male Barolo Shearwater Puffinus baroli. Timanfaya, Lanzarote, Canary Islands, December 2020. ©Cory’s
C) Male Barolo Shearwater Puffinus baroli. Montaña Clara, Canary Islands, December 2020. ©Cory’s
D) Male Barolo Shearwater Puffinus baroli. Timanfaya, Canary Islands, December 2020. ©Cory’s
The bird at La Gomera
While evaluating the size of a well-known Barolo Shearwater colony by quantifying the species’ vocal activity, I detected an ear-catching song that, fortunately, had been recorded loud and clear over a prolonged period between the nights of December 8th and December 23rd. The activity of this bird became more intense during the nights of 21st and 22nd, coinciding with a peak in Barolo Shearwater activity.
Figure 3. Vocal activity of both Boyd’s Shearwater Puffinus boydi and Barolo Shearwater Puffinus barolii at the colony during December 2020, S La Gomera. ©Cory’s
Here’s a compilation of the best recordings of the strange-sounding bird. Striking, uh?
My first impression was that of a very slow Barolo, with fewer notes in the exhalated phase of the song. There isn’t much material available for the species but, fortunately, very good records of both male and female are available on in The Sound Approach website (recorded by sound guru Magnus Robb), accompanied by an account on the species identification. All of the features described fit with the La Gomera bird. Here are my impressions of the bird, taking into account the vagrant context of the record:
The exhaled phase consists of 1–3 notes in Boyd’s. The central note is much longer than the notes that precede and follow it, which are almost vestigial. In contrast, the exhaled phase of Barolo consists of 3–5 (rarely up to 8) notes, all of them of a similar shape and duration. These differences lead to Boyd’s Shearwater to sound much slower than Barolo, somewhat reminiscent of an Oystercatcher.
The inhaled note in Boyd’s is longer and flatter compared to the short and arched inhaled note of a typical Barolo. Robb and TSA (2008) suggest it’s lower-pitched too, but at least in this bird it looks like the shape of the note has something to do with it: both Boyd’s and Barolo start this note at a similar frequency, but Boyd’s keeps it flat all along while Barolo increases the frequency to then drop it back to the starting frequency.
The first visible harmonic is quite far up from the fundamental frequency in Boyd’s, whereas it appears soon above the FF in Barolo. In general, Barolo shows more visible harmonics, which leads to a harsher sound, even in males (which are typically neater than females).
All the Boyd’s Shearwater songs recorded at La Gomera showed a tendency to progressively increase the overall frequency from the middle towards the end, whereas they typically remain flat in Barolo or show a steep change between 2–4 flat phrases and 2–3 higher pitched (but also flat) phrases. Again, my sample is limited to one bird, but I found this quite striking in this case.
Figure 5. Different songs of the presumed Boyd’s Shearwater Puffinus boydi recorded in S La Gomera, Canary Islands, December 2020. Note exhaled phases composed by one main note that can be followed and precede by two tiny notes. Overall frequency tends to increase from the middle towards the end and the inhaled note tens to be flat or slightly decreasing. Note also that most exhaled notes in A) are rounded, but they can sometimes be pointed as in B).
Finally, I tried do indicate all the differences in the following spectrograms, providing a side-by-side comparison between the two species. As for the future, it would be interesting to actually measure some of the key parameters and perform a proper statistical analysis to quantify the differences. However, nowadays there isn’t much material available (mine was the first Boyd’s Shearwater recording uploaded to xeno-canto!) and hence such analysis isn’t doable yet.
Figure 3. Comments on some of the most striking sound features in a vagrant Boyd's Shearwater.
Conclusions
The emerging pattern of occurrence of Boyd’s Shearwater in northern Macaronesia coincides with the bad weather that predominates in the area during late autumn and winter, so the chances of finding one offshore are low. However, it’s still worth paying attention to each small shearwater seen during this period, especially given how rare Barolo Shearwater is during these days. The ferries used to provide a good observation platform across the entire Archipelago but, sadly, the tendency is to replace the nice, old slow ferries (with comfortable outer decks) with new, fast ferries that have indoors platforms only (and which, due to their speed, are also more dangerous for cetaceans, especially Sperm Whale).
In this context, the best chance to connect with an extralimital Boyd’s comes from the Barolo colonies, where future acoustic surveys could reveal a more regular occurrence of this Cape Verdean endemic. In that respect, the bird shared the same vocal activity patterns with the local Barolo, what could indicate something more than a genuine vagrant. Despite having carefully checked all the female sounds recorded in this colony over December 2020, I failed to detect any Boyd’s Shearwater candidate, but female Shearwaters are far less vocal than males (females account for less than 10% of the total Barolo Shearwater vocal activity). That said, some Cape Verde Shearwaters Calonectris edwardsii regularly spend the summer in different Cory’s Shearwater Calonectris borealis colonies of the Canary Islands, vocalising along with the Cory’s, but breeding has never been confirmed. Given the steep decline of Barolo Shearwater on the Canary Islands, the limited access to the remaining Barolo Shearwater colonies challenges data collection, but we are working hard to reverse the situation of the species on this archipelago. Meanwhile, taking a look at the tracking data shows us just how much we still have to discover.
Acknowledgements
I want to thank first of all my workmates, especially Juan Bécares and Gustavo Tejera, who have been part of the team during all these years of work with Barolo Shearwater. I also want to thank all the skippers, the local and regional administrations and in general all the local people who have always helped us out while in the field and also with paperwork and project management. Regarding this post itself, I want to thank Magnus Robb - so far the only reference when it comes to Boyd’s Shearwater sounds - for his invaluable comments on the 2020 bird and Stephen Menzie for his master edition of the starting manuscript.
References
Copete, J. L., Lorenzo, J. A., Amengual, E., Bigas, D., Fernández, P., López-Velasco, D., Rodríguez, G. y García-Tarrasón, M. (2015). Observaciones de aves raras en España 2012 y 2013. Ardeola, 62: 453-508.
Flood, R. L., & van der Vliet, R. (2019). Variation and identification of Barolo Shearwater and Boyd’s Shearwater. Dutch Birding, 41, 215-237.
Flood, R. L., Olsen, K., Senfeld, T., Shannon, T. J., & Collinson, J. M. (2020). Audubon’s Shearwater collected in Skagerrak, Denmark, in September. Dutch Birding, 42, 147-156.
Gil-Velasco, M (2013). Mystery shearwater in Canary Islands in December 2012. Dutch Birding, 35, 186-189.
Robb, M., & Mullarney, K. (2008). Petrels night and day. The Sound Approach.
Zajková, Z., Militão, T., & González-Solís, J. (2017). Year-round movements of a small seabird and oceanic isotopic gradient in the tropical Atlantic. Marine Ecology Progress Series, 579, 169-183.