Streak-chested Antpitta in Costa Rica- One or Two Species?

During these apprehensive times of self quarantine, social distancing and much of life on pause, I often do what millions of other Earthlings tend to be doing; visually engage with the screen of a computer, a tablet, or a phone. Since I can’t stand messaging by phone or using it as a mini computer (I guess because I’m still stuck with this antiquated idea that phones are (were) for talking with other people), I find myself moving between the tablet and the laptop. I even use both at the same time but still try to remember to be productive, still try to make use of this time to work towards goals, digitally step my way to any number of future finish lines.

While attempting to use time in a productive manner, I also find myself veering off the path, musing about things I would love to study but for which I shouldn’t really invest as many hours. Sometimes, the errant thoughts gain hold, pull me into an inviting whirlpool that promises knowledge. But, as with any species of maelstrom, it can be a challenge to find the exit door, to leave. We all have our personal Hotel Californias; some are merely time consuming, others can be dangerous. Fortunately, one of the mental realms that magnetizes my attention involves nothing more than learning about birds and last night, the rabbit hole took the form of antpitta vocalizations. Not just any antpittas either but Hylopezus species. In non-birding vernacular, that means a smallish, brownish feathered ball with legs that calls over and over unseen and teasing from dense vegetation.

Having access to the Birds of the World doesn’t make it easy to extract myself from exploring the depths of avian information but then again, it’s a great place to mentally lounge. When one can explore birds by genus and family, it’s just too easy to roll with the avian taxonomy, look at their similarities, their subtle differences, and see where they occur. It’s fantastic to have the chance to look at images of those birds, even watch video footage, hear what they sound like. Having an inclination for the auditory side of existence, I find access to this latter aspect of bird knowledge particularly tempting.

I love to listen to what all of those birds sound like, my only complaint is that I can’t choose and listen to several at once for a direct, real time comparison (at least on the same device). Listening to some birds also sometimes reminds me of things I wanted to look into, one of those being the differences in songs shown by the Streak-chested Antpitta.

In Costa Rica, the Streak-chested Antpitta is an uncommon species of interior lowland and foothill rainforest on both slopes. Since it seems to be absent from various areas of rainforest habitat, it is likely subject to edge effects and probably has a preference for certain microhabitats inside forest such as flat or level areas.

I have known about the differences shown between birds on the Carribean and Pacific slopes of Costa Rica for some time but have never tried any playback experiments nor do I have the capacity or time to adequately measure and study the vocal differences found within that species. But, I can mention it here with the hope that others will be able to carry out molecular and extensive vocal studies to determine whether or not two or more species are involved when talking about Hylopezus perspicillatus.

Last night, my interest in this bird was renewed after listening to differences in vocalizations shown by two recently described species in the Spotted Antpitta complex from South America. Formerly lumped with Spotted Antpitta, both Alta Florest Antpitta and Snethlage’s Antpitta were split from that species based on a combination of morphological, molecular, and vocal differences. Most of the emphasis for splitting was placed on the differences in loudsongs between those taxa and since they still sounded fairly close, I figured I would take another look at Streak-chested Antpitta. Could I see differences between Streak-chested Antpitta songs using the same or similar parameters? Would that be even possible by comparing sonograms and would there be enough differences to argue for the occurrence of two species?

In brief, after reviewing recordings of this species from Honduras to Ecuador on Xeno-Canto and eBird, two main songs are evident; one pertaining to birds that occur from Honduras to western Panama on the Caribbean slope (the intermedius subspecies), and another to all other subspecies ranging from southern Costa Rica on the Pacific slope and the Canal Zone of Panama to Colombia and western Ecuador.

Although I didn’t measure vocal differences between both vocal groups, a cursory look at sonograms and listening to each type of song from several individuals appears to point at differences in frequency and structure or pattern of the song. There may also be differences in note structure, especially between the first note but off hand, note structure looks quite similar overall.

For example, in intermedius, the song seems to be mostly above 2 kilohertz in frequency and starts with a distinctive highest pitched note of the song, goes lower for the second note, goes up a bit in frequency for the third note and stays at that frequency for the next two notes before descending in frequency for the last three or four notes. In other words, the song starts high, goes low, then up and level before descending.

In the other subspecies, including birds from southern Costa Rica, the song seems to be mostly below 2 kilohertz and starts on a lower note, slightly ascends in frequency for two or three notes and then descends in frequency with the final note possibly at the same frequency as the starting note. In other words, the song goes slightly up and then back down.

Both types of songs seem to slow down in pace at the end and may also have the same number of notes. Although they may or may not significantly differ in pace, they do seem to differ in other ways. Would these differences be enough to argue for species status? To answer that question, we probably need a measured and adequate statistical analyses of these two song types backed by playback experiments. The results of that study alone might even be enough to make an argument for splitting this species but studies that also use morphological and molecular characters would be even better. If any grad student out there is looking for a project, this might be a good one…

On that note, the same can be said about the Thicket Antpitta (Hylopezus dives). While checking out vocalizations of the Streak-chested Antpitta, I was reminded that the Thicket also has disjunct populations from Central and South America and guess what? Their songs also differ.

This is a song of a bird from Costa Rica that is typical of populations from western Panama north to Honduras:

This is a song of a bird from Colombia typical for birds from the Darien and South America (although there might be some differences between birds from the Choco and eastern Colombia):

The differences are notable for pace, number of notes, and what seems to be note structure. With that in mind, it seems that these two main groups of Thicket Antpitta also merit further study. I wonder when I can start with playback experiments?