Interspecific Competition in Grallaria Antpittas: Observations at a Feeder Samuel S. Snow,1,2* Daniel J. Field,2,3,4 and Jacob M. Musser1,2 1 Department of Ecology and Evolutionary Biology, Yale University, P.O. Box 208106, New Haven, CT 06520-8106 USA *Corresponding author: [email protected] 2 Division of Vertebrate Zoology, Peabody Museum of Natural History, Yale University, P.O. Box 208118, New Haven, CT 06520-8118 USA 3 Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8109 USA 4Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560 USA ABSTRACT We describe an aggressive interaction between the extremely rare Jocotoco Antpitta (Grallaria ridgelyi) and a close relative, the Chestnut-naped Antpitta (Grallaria nuchalis). Since first discov- ered in 1997, ecological information about the Jocotoco Antpitta has begun to accrue; however, much remains to be learned about this rare species in its limited native range. The observations described here advance our knowledge of the behavioral ecology of this elusive species and con- tribute more broadly to our knowledge of interspecific competition in antpittas in general. We show that in avian systems in which playback experiments fail to detect competition, competition may still be prevalent, in this case manifesting in a nonvocal, physically aggressive interaction. We also raise new questions about the potential for temporal variation in interspecific competition in grallariids due to increased resource demands during nestling provisioning. KEYWORDS Grallariidae, Jocotoco Antpitta, interspecific competition, playback experiments, endangered species, Tapichalaca Introduction In doing so, we contribute to the knowledge of the habits of a unique, threatened, and little-known First discovered in 1997, the rare and extremely species, while also adding to our currently limited local Jocotoco Antpitta (Grallaria ridgelyi) is understanding of antpitta behavioral ecology. among the least numerous and least studied of the Intraspecific aggression in the Jocotoco antpittas (Passeriformes: Grallariidae) (Krabbe Antpitta has been observed only once. F. Men- et al. 1999; Krabbe and Schulenberg 2003). doza, a park ranger at the Tapichalaca Biological Because of their extremely secretive nature, rela- Reserve (lat 04°30ЈS, long 79°10ЈW; elevation tively little about general antpitta ecology and approximately 2,500 m) in southeastern Ecuador, behavior has been documented, beyond what can happened to encounter two Jocotoco Antpittas be gleaned from individual sightings and the apparently fighting over territory. He first heard study of breeding biology at active nest sites the two birds giving “challenging contact calls” (Krabbe and Schulenberg 2003; Greeney et al. and then, when they emerged onto the trail ahead 2008; Freile et al. 2010; Greeney 2012). Here we of him, he described the interaction between the describe, for the first time, direct competitive two individuals as reminiscent of two domestic interactions between G. ridgelyi and a close rela- fighting-cocks (Gallus gallus gallus): “The strong tive, the Chestnut-naped Antpitta (G. nuchalis). bill was used for fierce blows, and the victorious Bulletin of the Peabody Museum of Natural History 56(1):89–93, April 2015. © 2015 Peabody Museum of Natural History, Yale University. All rights reserved. • http://peabody.yale.edu 90 Bulletin of the Peabody Museum of Natural History 56(1) • April 2015 bird furiously followed its enemy, attacking its determining the range and distribution of the back and rump, until both birds disappeared in Jocotoco Antpitta (G. ridgelyi). However, Heinz the undergrowth again” (pers. comm. in Heinz (2002) concluded that there was no direct sup- 2002). Similar intense intraspecific aggression in port for this hypothesis: he documented signifi- other antpitta species has been previously docu- cant territorial overlap between the two species, mented, albeit rarely. For example, a direct fight and a distinct lack of response by each species to between a pair of wild Rufous Antpittas (Grallaria the territorial calls of the other. Anecdotally, only rufula) was observed, which resulted in the birds mild aggression between the Jocotoco Antpitta “rolling down the slope as a ball” (Krabbe and and other birds at worm-feeders has been previ- Schulenberg 2003). In captivity at the Bronx Zoo, ously reported. Worm-feeders are a recently a male Rufous-faced Antpitta (Grallaria erythro- developed phenomenon driven by the eco- tis) purportedly killed its female partner in a fight tourism industry as reliable means for tourists (Bell and Bruning 1976). to see generally furtive species such as antpittas. The increasing prevalence of these feeding sta- Ecology tions may encourage the association of antpittas and other vermivorous birds (Greeney 2012). Interspecific aggression in all antpittas, and in the Greeney (2013) suggested that in such settings Jocotoco Antpitta in particular, has rarely been the Jocotoco Antpitta is “apparently not aggres- directly documented. However, there is consider- sive towards the similarly-sized Chestnut-naped able circumstantial evidence to suggest that the Antpitta...” In contrast to these findings, our Jocotoco Antpitta and its close relative the Chest- observations provide the first concrete evidence nut-naped Antpitta (Krabbe et al. 1999) may com- for interspecific competition between G. ridgelyi pete for resources and territory. The Jocotoco and G. nuchalis. Antpitta is found on steep slopes of the Andes, in wet montane forest with a low canopy and exten- Materials and Methods sive bamboo cover between 2,300 and 2,680 m in elevation. This species primarily exploits the lower The events described here took place on the part of the forest (below 4 m), and is often seen morning of 19 March 2013 in the vicinity of a on the ground (Ridgely and Greenfield 2001; worm-feeder adjacent to the Tapichalaca Biolog- Heinz et al. 2005; Greeney 2013). The Chestnut- ical Reserve (see Greeney and Juiña 2010 for a naped Antpitta occurs in a more extensive geo- detailed site description). The Fundación de Con- graphical range (and a greater elevational range of servación Jocotoco (www.fjocotoco.org) estab- 2,000 to 3,000 m), but it occupies nearly identical lished the worm-feeder discussed here in 2005, habitat, and is found in sympatry with the Joco- specifically to attract Jocotoco Antpittas (Woods toco Antpitta where the latter species exists et al. 2011). (Krabbe et al. 1999; Ridgely and Greenfield 2001). We arrived at the feeder at 1006 h ECT Interestingly, both Grallaria ridgelyi and G. (Ecuador Time) accompanied by a guide from the nuchalis (along with several others in this genus) Fundación de Conservación Jocotoco. During our have been reported to engage facultatively in feed- visit we observed two adult Jocotoco Antpittas, a ing associations, periodically following army ant single Chestnut-naped Antpitta, and direct com- swarms, as well as large mammals (including petitive interactions between these two species humans) that are crashing through vegetation (Figure 1). The first adult Jocotoco Antpitta was (Greeney 2012). Stomach content analysis of G. already present at the feeder on our arrival. It ridgelyi and G. nuchalis has revealed nearly iden- began collecting earthworms that were regularly tical diets, including millipedes, beetles, ants, and tossed onto a stone platform by the guide. A sec- arthropod larvae (Krabbe and Schulenberg 2003). ond Jocotoco Antipitta adult soon joined the first, In spite of these ecological similarities, previ- and they alternated gathering worms from the ous work has failed to show any association feeder until the supply was exhausted at 1048 h between the two species. Heinz (2002) hypothe- (see Figure 1B). A typical feeding cycle consisted of sized that Grallaria ridgelyi and G. nuchalis may the antpitta ingesting some worms, followed by a compete for resources, with implications for period of gathering worms to store in the bill or Interspecific Competition in Grallaria Antpittas • Snow et al. 91 FIGURE 1. Jocotoco Antpitta, Grallaria ridgelyi, and Chestnut-naped Antpitta, G. nuchalis, at a worm-feeder at the Tapichalaca Reserve, southern Ecuador, on 19 March 2013. A, Adult G. ridgelyi performing characteristic hoo-coo call, 1034 h ECT. B, Adult G. ridgelyi collecting the last remaining worms from the feeding platform, 1048 h ECT. C, Adult G. nuchalis approaching empty feeding platform, 1055 h ECT, with feathers ruffled in response to approach from G. ridgelyi. D, Adult G. nuchalis standing at empty feeding platform at 1104 h ECT, immedi- ately before being chased away by an adult G. ridgelyi. perhaps crop, and then leaving for several minutes grrr call has been described as a territorial chal- before returning and repeating this process. Our lenge-seeking call (Heinz 2002). Our observations companion from the Fundación Jocotoco, who suggest that this call may also be used as a contact was familiar with these local birds, indicated that call within pairs. these two adults were a mated pair carrying worms One individual Chestnut-naped Antpitta first to a nestling nearby, which we did not directly appeared in the area at 1053 h, attracted by whis- observe. Throughout this interval the two Joco- tles from the Fundación Jocotoco guide. It toco Antpitta individuals often called to one approached tentatively from the opposite side of another with the characteristic hoo-coo call, to the clearing relative to the Jocotoco Antpittas at a which they owe their common name (Ridgely and moment when no Jocotoco Antpittas were pres- Greenfield 2001; see Figure 1A). We noted that ent. The Chestnut-naped Antpitta remained at the one individual would always call first, followed empty feeding platform until 1055 h, and within seconds by a response with the same call departed quickly when a Jocotoco Antpitta from the second individual. This hoo-coo or ho- arrived (see Figure 1C). 92 Bulletin of the Peabody Museum of Natural History 56(1) • April 2015 At 1059 h, again when no Jocotoco Antpittas others (Woods et al. 2011; Greeney 2013).