Proposal (967) to South American Classification Committee

Note from Remsen: This is a proposal submitted to and passed unanimously (10 to 0) by NACC (2023-B-2), modified by me slightly for SACC.

Transfer the subspecies minor and cinerascens from Myiodynastes chrysocephalus to M. hemichrysus, thereby adding Myiodynastes hemichrysus to SACC list

The NACC Checklist currently lists four species of flycatchers in the genus Myiodynastes, including two species, M. hemichrysus and M. chrysocephalus, identified as constituting a superspecies. These species are sometimes considered to be conspecific (e.g., Cory and Hellmayr 1927), but when they are separated, M. hemichrysus of Costa Rica and western Panama is generally treated as monotypic, whereas M. chrysocephalus includes, in addition to nominate chrysocephalus of the Andes of Peru, Bolivia, and northwestern Argentina, subspecies cinerascens of northern Colombia and Venezuela and subspecies minor of extreme eastern Panama south to extreme northern Peru. Although the subspecies included in each species are not specified in the accounts in AOU (1998), it is clear from the distributional statements that this is the subspecies arrangement.

Plumage is somewhat variable within the complex. According to Cory and Hellmayr, hemichrysus:

“differs immediately from the southern race by the much deeper yellow, wholly unstreaked under parts, leaving only the chin white, and by lacking the conspicuous rufous edges to the rectrices. In wing-markings it more nearly resembles M. c. chrysocephalus.”

The typical allocation of subspecies thus follows the most conspicuous plumage features, and this allocation is followed by most global sources (e.g., Dickinson and Christidis 2014, Clements et al. 2021, Gill et al. 2021). Birdlife, however, has recently partitioned the subspecies in a different way, transferring minor and cinerascens to M. hemichrysus. The rationale for this change was as follows:

“Races minor and cinerascens here transferred from M. chrysocephalus because their dawn songs (repeated “kweee!-tee-tu”) and daytime songs (strident “skeeeuw!”) are identical to those of present species [i.e., M. hemichrysus] and very different (scores of 3 for each) from those of chrysocephalus (respectively “kwee!-tlu-tee” and “ku-weet!.. weet!”, the “weet!” sharply rising and much higher-pitched than first note)…”

They further noted that M. chrysocephalus also differs from M. hemichrysus by its longer wing and tail and much buffier and more restricted rufous edges to the tail.

The vocal descriptions above are condensed versions of the conclusions of Boesman (2016), who compared vocalizations of all four taxa in this complex. The similarity of the dawn and day songs of hemichrysus, minor, and cinerascens are apparent from his figure and measurements comparing the vocalizations (see following pages), as are the differences with chrysocephalus. Boesman’s summary of the differences is as follows:

“Voice of Myiodynastes hemichrysus is about identical to M. c. minor and M. c. cinerascens. We would need a large number of samples to prove any consistent difference, but in any case it would be very small. (Possibly the note shape is slightly different, with M. hemichrysus having a little notch at the right side of the day-time song). Difference score for these taxa is thus 0 (or possibly 1).

“Difference with chrysocephalus at the other hand is quite noticeable: Day-time song has 2 (or 3) distinct notes (score 3) with very different note shape (score 1) and slightly longer overall length (score 1). Dawn song ends with a fairly emphasized rising note (unlike all other races which end in subdued notes) (score 2) and note shape of first note different (score 1). The fact that both dawn song and day-time song are clearly different makes this case even more convincing.”

“Myiodynastes hemichrysus

dawn-song: a repeated "kwee!-tee-t-tu" (n=1)

min. freq. 2140Hz

max. freq. 5600Hz

total length 0.39s

length 1st note 0.13s

“day-time song: a repeated loud strident "skeeew!" (n=6)

min. freq. 1200-1550Hz

max. freq. 5350-5830Hz

total length 0.18-0.25s

“M. c. minor

dawn-song: a repeated "kwee!-tee-tu" or "kwee!-tee-tu-ti-lu" (n=3)

min. freq. 1380-1590Hz

max. freq. 5290-5740Hz

total length 0.32-0.43s

length 1st note 0.12-0.14s

“day-time song: a loud strident "skeeeuw!" (n=6)

min. freq. 1030-1450Hz

max. freq. 5000-5550Hz

total length 0.15-0.29s

“M. c. cinerascens

dawn-song: a repeated "kwee!-tee-tu" (n=2)

min. freq. 1300-1320Hz

max. freq. 5030-5120Hz

total length 0.37-0.39s

length 1st note 0.15-0.16s

“day-time song: a loud strident "skeeew!" or "skeeeuuw!" (n=6)

min. freq. 1060-1400Hz

max. freq. 4540-6340Hz

total length 0.17-0.28s

“M. c. chrysocephalus

dawn-song: a repeated "kwee!-tlu-tee" (n=2)

min. freq. 1950-2050Hz

max. freq. 5220-5300Hz

total length 0.42-0.46Hz

length 1st note 0.12-0.13s

“day-time song: a loud strident "ku-weet!" or "ku-weet!.. weet!" (weet! sharply rising and much higher-pitched than first note) (n=8)

min. freq. 1150-1380Hz

max. freq. 4000-5300Hz

total length 0.22-0.66s

# of notes 2-3”

Sample sizes for these comparisons aren’t huge, especially for dawn songs, but recordings available on the xeno-canto and Macaulay Library websites confirm the differences between the two species and clearly place minor and cinerascens with M. hemichrysus rather than M. chrysocephalus.

These differences were also recognized in the field guide to the birds of Peru (Schulenberg et al. 2007), in which a clear distinction was made between the vocalizations of minor of northern Peru and those of the more widespread chrysocephalus, although without comparing the vocalizations of minor with those of Central American hemichrysus.

Recommendation:

I recommend that we transfer subspecies minor (and extralimital subspecies cinerascens) from M. chrysocephalus to M. hemichrysus. Although plumage favors the traditional placement of minor and cinerascens in chrysocephalus, this is contradicted by the vocal data, which indicate that these two subspecies belong in M. hemichrysus. Vocalizations are innate and primary indicators of species limits and affinities in suboscine birds, and in this case they demonstrate that the traditional allocation of subspecies in the complex was in error. If adopted, this change would add M. hemichrysus to the SACC main list.

References:

Boesman, P. 2016. Notes on the vocalizations of Golden-crowned Flycatcher (Myiodynastes chrysocephalus) and Golden-bellied Flycatcher (Myiodynastes hemichrysus). HBW Alive Ornithological Note 141. In: Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/932065 on 10 August 2016).

Schulenberg, T. S., D. F. Stotz, D. F. Lane, L. B. McQueen, J. P. O’Neill, and N. J. Schmitt. 2007. Birds of Peru. Princeton University Press, Princeton.

Terry Chesser, February 2023

Comments from Remsen (as in my NACC comments): “YES. Of course we would prefer a peer-reviewed paper on those vocalizations, but I think the differences shown by Boesman, and consistent with those mentioned by Schulenberg et al., shift the burden of proof to justifying maintaining the current treatment. Voice is everything in cases of species limits in parapatric and sympatric tyrannids, and so I think we are on solid ground to revise our classification based on the latest information on voice.”

Comments from Robbins: “YES. Both dawn song and calls support transfer of the subspecies of minor and cinerascens from Myiodynastes chrysocephalus to M. hemichrysus. I agree we don't need to wait for a peer-reviewed paper to make this move. Needless to say, it will be interesting to eventually see what genetic data demonstrate.”

Comments from Lane: “YES to shifting minor and cinerascens to M. hemichrysus, leaving M. chrysocephalus monotypic. The voice here makes this a fairly easy decision, but I do chafe on one detail: some verbiage has been spent discussing dawn song distinctions, but I cannot locate a recording of dawn song from true hemichrysus (which seems surprisingly poorly sampled in general), and Boesman's voice assessment maddeningly does not specify what recordings he reviewed (including which are the sources of the sonograms)! I really would like to compare the dawn songs of hemichrysus and minor just to feel a little better about this taxonomic shift.”

Comments from Areta: “YES to a monotypic M. chrysocephalus and to moving minor and cinerascens to M. hemichrysus, the differences between the northern and southern South American populations of "chrysocephalus" have puzzled me for several years, and were in my "to do" list. I never compared songs against hemichrysus, but the decision is straightforward. As per the Boesman pieces, I agree with Dan, and I have also repeatedly pointed out their deficiencies, which is a pity, given the amount of work performed.”

Comment from Peter Boesman: “I noticed in the proposal 967 (Golden-bellied Flycatcher complex) that Dan Lane commented he could not find a dawn song of the hemichrysus taxon. There is one in Macaulay Library:”

ML144068 Golden-bellied Flycatcher Macaulay Library

Comment from Stiles: “YES to moving these two subspecies from chrysocephalus into hemichrysus: in such a case, vocalizations clearly trump the rather weak plumage differences.”

Comment from Del-Rio (who has Pacheco vote): “YES.”

Comments from Claramunt: “NO. Plumage is also innate and primary indicator of species limits and affinities in suboscine birds. If there is a conflict between vocal and plumage data, then we should examine that conflict and seek additional data to clarify the situation, not accept whatever the vocal data suggest at face value.”

Comments from Bonaccorso: “NO. We need to aim toward a more integrative taxonomy when making these decisions. Plumages tell one story, songs tell another, and we don´t have genetic or other data to solve the ‘tie.’”

Comments from Oscar Johnson (voting for Jaramillo): “YES, with a nod toward the concerns raised by others about the discordance between plumage and song. Both plumage and song do of course have a genetic basis in suboscines, but given how important song is for mate recognition, I'm much more inclined to place emphasis on song in species delimitation for species complexes in which plumage is broadly similar. It is hard to argue with the similarity in vocalizations, which are really nearly identical in all taxa north of the Marañón Valley, and quite distinct to the south. The song differences in particular are remarkably consistent, but I will note that there does appear to be some variation in the daytime calls, with some recordings of hemichrysus/minor/cinerascens having some rising notes, but these are usually given singly and not in combination with the arched note as in chrysocephalus. That said, I agree that nominate hemichrysus is quite distinctive in plumage compared to all other taxa in the group, and I wonder about the possibility of a three species treatment; hemichrysus, minor (including cinerascens), and chrysocephalus, which would emphasize the distinct combinations of differences in both song and plumage. More work is clearly needed.”