Proposal (642) to South American Classification Committee

Elevate subspecies Agelaioides badius fringillarius (Pale Baywing) to species rank

In my recent HBW chapter on the Icteridae (Fraga 2011), I treated the Bay-winged Cowbird/Baywing as two separate species, Gray Baywing (A. badius) and Pale Baywing (A. fringillarius). (See SACC proposal 641 for rationale for use of “Baywing.). Below is the rationale for the split.

The Pale Baywing was described as Icterus fringillarius by Spix in 1824 from Minas Gerais, Brazil. Up to Friedmann´s classical monograph (1929), it was treated as a full species (Agelaioides fringillarius). Hellmayr (1937) treated fringillarius as a well-marked subspecies of Grayish Baywing. Jaramillo and Burke (1999) suggested that the Pale Baywing might deserve species rank. The official Brazilian checklist recognizes this form as a species. In Brazil the Pale Baywing is regarded as an endemic species of the Caatinga biome (Pacheco 2000).

After observing Pale Baywings in NE Brazil, I accepted this view in the HBW (Fraga 2011). This proposal presents the case for species rank for the Pale Baywing. The Grayish Baywing would then include only two subspecies, badius and bolivianus.

1) Allopatric status of the Pale Baywing and Grayish Baywing

Most recent references (Ridgely & Tudor 1989, Fraga 2011) show the ranges of Grayish and Pale Baywings as separated by a large geographic gap extending from Mato Grosso do Sul to central Minas Gerais. The natural vegetation in this gap was mostly cerrado.

Willis & Oniki (1982) reported Grayish Baywings from São Paulo state, Brazil. This record was repeated by Fraga (1986, 1998) and Ridgely & Tudor (1989). However, it is based on mistaken identifications of mimetic young Screaming Cowbirds (Willis & Oniki 1993), and therefore invalid. Other recent records of Baywings from central Brazil (e. g. Goiás state, Bagno & Rodrigues 1998) may be based on a similar mistake, because the authors saw the putative Baywings flocking with Chopi Blackbirds, a main host of Screaming Cowbirds.

At the northern edge of their range in Paraguay Grayish Baywings do not occur in the Atlantic Forest or Cerrado formations (Hayes 1995, and my pers. obs.). Grayish and Pale baywing distributions are a good example of the well-known Chaco-Caatinga biogeographical disjunction (Sick 1993) shared with many species of plants and animals. Although baywings occur in human-modified habitats, there is no evidence of a range expansion in central Brazil.

2) Plumage differences

The overall sandy coloration of Pale Baywings is unique in the genus. The dusky areas around the eyes of Pale Baywings extend further down in the postocular region than in Grayish baywings.

3) Behavioral differences

Group singing is more developed in Grayish than in the Pale Baywing (Fraga & D’Angelo Neto 2014). An agonistic collective display of Grayish Baywings (“Leaf Gathering”; Fraga 1981) was not observed in Pale Baywings. Cooperative breeding is found in all baywings, but seems more developed in Pale Baywings (Fraga & D´Angelo Neto 2014).

4) Vocal differences

I use here examples available in the xeno-canto website. I also include four figures with sonograms from my recordings of Grayish Baywings (nominate badius and bolivianus) and Pale Baywings.

Figure 1 shows the contact calls of Grayish Baywings from subspecies badius (A) and bolivianus (B). Localities are Estancia La Candelaria, Buenos Aires, Argentina, and P. N. Tunari, Cochabamba, Bolivia. The first calls are “chucks” resembling those found in many species of quiscaline icterids (Orians & Angell 1985). Far more distinctive is the second call, a short loud whistle with variable harmonics, transcribed as “peeoh” by Friedmann (1929). It is commonly heard from flying individuals, but perched individuals commonly exchange such calls before taking flight. It is also heard from perched individuals lacking visual contact, such as before sunrise or in dense fog. Sometimes “peooh” whistles are included in songs. Both calls show some geographic variation but remain recognizable.

I never heard “peeoh” calls from Pale Baywings. Their commonest calls (fig. 2) are loud, hook-shaped ascending notes, with a variable number of harmonics. Perched individuals at roosts produce a considerable amount of noise with these calls. Groups flying away from roosts also produce the calls. In such contexts the hook-shaped notes appear to be contact calls. In my own recordings from Minas Gerais hook-shaped calls may have many variants, which can be produced by a single bird in less than a minute (as in fig. 2). In the last call the individual was flying away. During my observations of nesting groups bursts of loud hook-shaped calls occurred when Pale Baywing groups detected and attacked nest predators, also functioning as an alarm call.

The hook-shaped calls are the most distinctive vocalizations of Pale Baywings, as nothing similar occurs in Grayish Baywings. Examples from xeno-canto can be found at 2.7 to 4 s in XC84580 (obtained in Minas Gerais). In XC4548 from Pernambuco there are 8 such calls (the sound is somewhat saturated in this cut).

Other calls of Grayish and Pale Baywings look similar and have similar behavioral contexts, such as the scolding call (a harsh “krrp”) and the begging calls of fledglings. See examples XC84580 and XC4548.

The songs of Grayish and Pale Baywings show recognizable differences. Figure 3 shows one song from a breeding banded individual from Estancia La Candelaria, Buenos Aires. Good examples from Grayish Baywings songs can be found in xeno-canto: Brazil (XC84387 and XC128630), Paraguay (XC15608), Uruguay (XC7889) and Argentina (XC50789). Note the overall similarity across a large geographic area. Songs of Grayish Baywings contain ascending and descending whistles, also trills, series of clicks and flute-like notes.

Figure 4 shows one song from a Pale Baywing attending a nest near Francisco Sá, Minas Gerais. Examples of similar song fragments from Pale Baywings are available in xeno-canto: XC84579 and XC84580. Songs of Pale Baywings are simpler and less musical, lacking trills and flute-like notes, and contain mostly slow descending whistles. Songs are slower, softer, and more hesitant in Pale Baywings.

Summary

Besides plumage, there are important differences in social behavior, contact calls and song between Grayish and Pale Baywings.

References

Bagno, M. A., and F. H. G. Rodrigues. 1998. Novos registros de aves para o estado de Goiás, Brasil. Ararajuba 6:64-65.

Fraga, R. M. 1991. The social system of a communal breeder, the baywinged cowbird Molothrus badius. Ethology 89:195-210.

Fraga, R. M. 2011. Family Icteridae, New World Blackbirds, p 684-801. In: del Hoyo J., Elliot A. & Christie D. (eds.) Handbook of the Birds of the World vol. 16, Lynx Edicions, Barcelona, Spain.

Fraga, R. M. and S. D´Angelo Neto. 2014. Natural history notes and breeding of the Pale Baywing (Agelaioides fringillarius) in northern Minas Gerais, Brazil. Revista Brasileira de Ornitologia, 22: 238-241.

Friedmann, H. 1929. The Cowbirds. C. C. Thomas, Springfield, Illinois, USA.

Hayes, F. E. 1995. Status, distribution and biogeography of the birds of Paraguay. Monographs in Field Ornithology no. 1. American Birding Association.

Hellmayr, C. E. 1937. Catalogue of birds of the Americas. Vol. 12 Icteridae. Field Museum Natural History 13: 1-228.

Jaramillo, A., and P. Burke. 1999. New World Blackbirds. The icterids. Princeton Univ. Press, Princeton, N. Jersey.

Orians, G. and T. Angell.1985. Blackbirds of the Americas. University of Washington Press.

Pacheco, J. F. 2000. A ornitologia descobre o sertão: um balanço do conhecimento da avifauna da caatinga dos primordios aos annos 1950, p. 11-70. In: Straube F. C., Argel-de-Oliveira M. M. & Candido-Jr. J. F. (eds.) Ornitologia Brasileira no século XX. Universidade do Sul de Santa Catarina and Sociedade Brasileira de Ornitologia, Curitiba, Brazil.

Ridgely, R. S., and G. Tudor. 1989. The Birds of South America. Vol. 1, the Oscine Passerines. The University of Texas Press, Austin.

Sick, H. 1993. Birds in Brazil. A Natural History. Princeton University Press, Princeton NJ.

Willis, E. O., and Y. Oniki. 1985. Bird specimens new for the state of Sao Paulo, Brazil. Revista Brasileira Biologia 45:105-108.

Willis, E. O., and Y. Oniki. 1993. New and reconfirmed birds from the state of Sao Paulo, Brazil, with notes on disappearing species. Bulletin British Ornithologists’ Club113: 23-?.

Rosendo M. Fraga, August 2014

Figure 1. Contact calls of Grayish Baywings (“chuck” and “peeoh”) from Argentina and Bolivia

Figure 2. Hook-shaped calls of a single individual Pale Baying, showing variants.

Figure 3. Song of a banded Grayish Baywing near its nest

Figure 4. Song of a Pale Baywing near its nest

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Comments from Zimmer: “YES”. This squares with my field observations regarding vocal and morphological differences between these two taxa, and it sounds as if there may be some differences in behavior/social structure as well. These differences also reflect a biogeographical pattern seen in Gray-crested vs. Caatinga cacholotes (which we recognize as distinct species), the chaco vs. caatinga subspecies of Nystalus striolatus (which SACC does not recognize as distinct), the wagtail-tyrants (Stigmatura) and others. The only question in my mind is whether the handful of spectrograms presented in the proposal, along with the other evidence presented, meets our standard of rigor as regards published analysis. My perception that it does (barely) is no doubt influenced by my own field-based preconceptions on this issue, and I could certainly understand others feeling that we should wait for a more thorough, peer-reviewed, published analysis.”

Comments from Robbins: “YES. Fraga does a good job of highlighting the differences between these two taxa and this is an excellent example of how and why online audio resources should be used in supporting proposals, regardless if they have been formally published. This committee often provides a more rigorous evaluation than many published papers that lacked proper vetting (i.e., inappropriate reviewers, editors ignoring appropriate reviewer’s comments, etc.).”

Comments from Stiles: “YES, the evidence presented by Fraga seems quite convincing.”

Comments from Jaramillo: “YES – I am very excited that Fraga has been able to put together these observations, recordings and make a solid case. The information available to us for the Icterids book was very scant, but even with what was available it seemed a very convincing case for two species at the time. Now even more so.

As a note on the English Name, I would very much prefer that the concise Baywing be left for badius rather than Gray or Grayish Baywing. There is precedence for this, Pale Sand Martin for Riparia diluta, versus Sand Martin for …. well the Bank Swallow Riparia riparia. So Baywing and Pale Baywing still seem appropriate, and these names have now been out for nearly 15 years or so.

Response from Remsen: “Concerning Alvaro’s comment above … If the proposal passes, there is NO WAY one could be called Baywing and the other Something Baywing. This violates every principle of standardization of English names.”

Comments from Pacheco: “YES. The arguments raised by Chendo are perfectly in line with my experience with these taxa. I totally agree with the proposal, a case already anticipated by Jaramillo & Burke’s Monograph.”

Comments from Remsen: “NO. The plumage differences mean only that they are separate taxa, worthy of recognition minimally at subspecies rank. The differences in social systems seem to be only a matter of degree or based on small N. Intraspecific geographic variation in social system structure is known for several species. That leaves the vocal data, which I am convinced from what I see provide solid evidence for species rank for the two taxa …. but the data are not published per se. Chendo could take this proposal and turn it into a short MS for RBO with just a little additional work. Although HBW and CBRO, those treatments are not based, as far as I can tell, on published primary literature.”

Comments from Cadena: “NO. I'm with Van on this one - see my comments on proposal 630 for my views on cases involving unpublished analyses regardless of how different taxa may look. Here the most important piece of the story seem to be vocalizations, but these have not been fully analyzed with appropriate sample sizes, formal tests, etc., and no paper documenting results has been published.”