Interspecific Competition in Grallaria Antpittas: Observations at a Feeder

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1 Interspecific Competition in Grallaria Antpittas: Observations at a Feeder Samuel S. Snow, 1,2* Daniel J. Field, 2,3,4 and Jacob M. Musser 1,2 1 Department of Ecology and Evolutionary Biology, Yale University, P.O. Box , New Haven, CT USA *Corresponding author: samuel.snow@yale.edu 2 Division of Vertebrate Zoology, Peabody Museum of Natural History, Yale University, P.O. Box , New Haven, CT USA 3 Department of Geology and Geophysics, Yale University, P.O. Box , New Haven, CT USA 4 Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 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 discovered 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 contribute 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 First discovered in 1997, the rare and extremely local Jocotoco Antpitta (Grallaria ridgelyi) is among the least numerous and least studied of the antpittas (Passeriformes: Grallariidae) (Krabbe et al. 1999; Krabbe and Schulenberg 2003). Because of their extremely secretive nature, relatively little about general antpitta ecology and behavior has been documented, beyond what can be gleaned from individual sightings and the study of breeding biology at active nest sites (Krabbe and Schulenberg 2003; Greeney et al. 2008; Freile et al. 2010; Greeney 2012). Here we describe, for the first time, direct competitive interactions between G. ridgelyi and a close relative, the Chestnut-naped Antpitta (G. nuchalis). In doing so, we contribute to the knowledge of the habits of a unique, threatened, and little-known species, while also adding to our currently limited understanding of antpitta behavioral ecology. Intraspecific aggression in the Jocotoco Antpitta has been observed only once. F. Mendoza, a park ranger at the Tapichalaca Biological Reserve (lat S, long W; elevation approximately 2,500 m) in southeastern Ecuador, happened to encounter two Jocotoco Antpittas apparently fighting over territory. He first heard the two birds giving challenging contact calls and then, when they emerged onto the trail ahead of him, he described the interaction between the two individuals as reminiscent of two domestic fighting-cocks (Gallus gallus gallus): The strong bill was used for fierce blows, and the victorious Bulletin of the Peabody Museum of Natural History 56(1):89 93, April Peabody Museum of Natural History, Yale University. All rights reserved.

2 90 Bulletin of the Peabody Museum of Natural History 56(1) April 2015 bird furiously followed its enemy, attacking its back and rump, until both birds disappeared in the undergrowth again (pers. comm. in Heinz 2002). Similar intense intraspecific aggression in other antpitta species has been previously documented, albeit rarely. For example, a direct fight between a pair of wild Rufous Antpittas (Grallaria rufula) was observed, which resulted in the birds rolling down the slope as a ball (Krabbe and Schulenberg 2003). In captivity at the Bronx Zoo, a male Rufous-faced Antpitta (Grallaria erythrotis) purportedly killed its female partner in a fight (Bell and Bruning 1976). Ecology Interspecific aggression in all antpittas, and in the Jocotoco Antpitta in particular, has rarely been directly documented. However, there is considerable circumstantial evidence to suggest that the Jocotoco Antpitta and its close relative the Chestnut-naped Antpitta (Krabbe et al. 1999) may compete for resources and territory. The Jocotoco Antpitta is found on steep slopes of the Andes, in wet montane forest with a low canopy and extensive bamboo cover between 2,300 and 2,680 m in elevation. This species primarily exploits the lower part of the forest (below 4 m), and is often seen on the ground (Ridgely and Greenfield 2001; Heinz et al. 2005; Greeney 2013). The Chestnutnaped Antpitta occurs in a more extensive geographical range (and a greater elevational range of 2,000 to 3,000 m), but it occupies nearly identical habitat, and is found in sympatry with the Jocotoco Antpitta where the latter species exists (Krabbe et al. 1999; Ridgely and Greenfield 2001). Interestingly, both Grallaria ridgelyi and G. nuchalis (along with several others in this genus) have been reported to engage facultatively in feeding associations, periodically following army ant swarms, as well as large mammals (including humans) that are crashing through vegetation (Greeney 2012). Stomach content analysis of G. ridgelyi and G. nuchalis has revealed nearly identical diets, including millipedes, beetles, ants, and arthropod larvae (Krabbe and Schulenberg 2003). In spite of these ecological similarities, previous work has failed to show any association between the two species. Heinz (2002) hypothesized that Grallaria ridgelyi and G. nuchalis may compete for resources, with implications for determining the range and distribution of the Jocotoco Antpitta (G. ridgelyi). However, Heinz (2002) concluded that there was no direct support for this hypothesis: he documented significant territorial overlap between the two species, and a distinct lack of response by each species to the territorial calls of the other. Anecdotally, only mild aggression between the Jocotoco Antpitta and other birds at worm-feeders has been previously reported. Worm-feeders are a recently developed phenomenon driven by the ecotourism industry as reliable means for tourists to see generally furtive species such as antpittas. The increasing prevalence of these feeding stations may encourage the association of antpittas and other vermivorous birds (Greeney 2012). Greeney (2013) suggested that in such settings the Jocotoco Antpitta is apparently not aggressive towards the similarly-sized Chestnut-naped Antpitta... In contrast to these findings, our observations provide the first concrete evidence for interspecific competition between G. ridgelyi and G. nuchalis. Materials and Methods The events described here took place on the morning of 19 March 2013 in the vicinity of a worm-feeder adjacent to the Tapichalaca Biological Reserve (see Greeney and Juiña 2010 for a detailed site description). The Fundación de Conservación Jocotoco ( established the worm-feeder discussed here in 2005, specifically to attract Jocotoco Antpittas (Woods et al. 2011). We arrived at the feeder at 1006 h ECT (Ecuador Time) accompanied by a guide from the Fundación de Conservación Jocotoco. During our visit we observed two adult Jocotoco Antpittas, a single Chestnut-naped Antpitta, and direct competitive interactions between these two species (Figure 1). The first adult Jocotoco Antpitta was already present at the feeder on our arrival. It began collecting earthworms that were regularly tossed onto a stone platform by the guide. A second Jocotoco Antipitta adult soon joined the first, and they alternated gathering worms from the feeder until the supply was exhausted at 1048 h (see Figure 1B). A typical feeding cycle consisted of the antpitta ingesting some worms, followed by a period of gathering worms to store in the bill or

3 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 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, immediately before being chased away by an adult G. ridgelyi. perhaps crop, and then leaving for several minutes before returning and repeating this process. Our companion from the Fundación Jocotoco, who was familiar with these local birds, indicated that these two adults were a mated pair carrying worms to a nestling nearby, which we did not directly observe. Throughout this interval the two Jocotoco Antpitta individuals often called to one another with the characteristic hoo-coo call, to which they owe their common name (Ridgely and Greenfield 2001; see Figure 1A). We noted that one individual would always call first, followed within seconds by a response with the same call from the second individual. This hoo-coo or ho- grrr call has been described as a territorial challenge-seeking call (Heinz 2002). Our observations suggest that this call may also be used as a contact call within pairs. One individual Chestnut-naped Antpitta first appeared in the area at 1053 h, attracted by whistles from the Fundación Jocotoco guide. It approached tentatively from the opposite side of the clearing relative to the Jocotoco Antpittas at a moment when no Jocotoco Antpittas were present. The Chestnut-naped Antpitta remained at the empty feeding platform until 1055 h, and departed quickly when a Jocotoco Antpitta arrived (see Figure 1C).

4 92 Bulletin of the Peabody Museum of Natural History 56(1) April 2015 At 1059 h, again when no Jocotoco Antpittas were visible, a Chestnut-naped Antpitta appeared and approached tentatively, taking a few steps and then pausing for several seconds, becoming erect and alert before again proceeding forward another few steps. It advanced in this way until it arrived at the feeder at 1103 h (see Figure 1D). At 1104 h, a Jocotoco Antpitta emerged from the ground vegetation and began to run toward the Chestnutnaped Antpitta, which quickly retreated. The Jocotoco Antpitta did not pursue the Chestnutnaped Antpitta out of sight, and the chase ended as soon as the Chestnut-naped Antpitta disappeared into the underbrush at the edge of the clearing. The third and final interaction between the two species occurred when the Chestnut-naped Antpitta returned to find a Jocotoco Antpitta at the empty feeding platform at 1109 h. At the appearance of the Chestnut-naped Antpitta, the Jocotoco Antpitta became visibly agitated, ruffled its feathers, and chased the Chestnut-naped Antpitta far from the clearing at high speed, following it up a slope and out of sight. It was unclear whether both or just one of the adult Jocotoco Antpittas engaged in this aggressive behavior. Discussion This aggressive interaction is a curious window into the ecology of an extremely rare and littleknown bird. In contrast to previous findings, the Jocotoco Antpitta may indeed engage in resource competition with other closely related, sympatric Grallaria antpittas. Though playback experiments have failed to reveal interspecific aggression between these two species, we have observed directly that they do interact aggressively, with the larger Jocotoco Antpitta appearing to represent the dominant combatant (Heinz 2002). It could be that in certain contexts playback experiments may simply be inconclusive, failing to reveal physical conflict over food resources, as opposed to mere vocal conflict. In this case we have shown that aggressive interactions between G. ridgelyi and G. nuchalis apparently consist of silent chasing and posturing rather than vocalizing. These would naturally be overlooked in a playback experiment. Perhaps more curious is the contrast between our findings of violent interspecific aggression between Grallaria ridgelyi and G. nuchalis and those of previous observations at this feeder and others (Woods et al. 2011; Greeney 2013). The Jocotoco Antpittas we observed were purportedly provisioning a nestling at the time. It may be that competition for food is at its highest during the nestling provisioning period, and that previous reports derive from nonbreeding periods. If this is the case, it could indicate previously underappreciated temporal variation in interspecific competition in grallariids. Future research may focus on whether sympatric antpittas stagger breeding periods so as not to overlap during this potentially demanding time. Acknowledgments We would like to thank our friends at the Fundación de Conservación Jocotoco and the Tapichalaca Biological Reserve for their admirable work to conserve these fascinating birds. We would also like to thank Dr. Kristof Zyskowski of the Yale Peabody Museum of Natural History and Dr. Harold Greeney of the Yanayacu Biological Station for reviewing this manuscript and providing many helpful comments. The authors acknowledge the following sources of funding: Yale University (Snow, Musser, and Field); National Sciences and Engineering Research Council Canada Graduate Scholarship D and Smithsonian Predoctoral Fellowship (to Field); and National Science Foundation Graduate Research Fellowship under grant no. DGE (Snow and Musser). Received 30 May 2014; revised and accepted 19 December Literature Cited BELL, J., AND D. BRUNING Hatching and handrearing the Rufous-faced Antpitta. Notes on antbirds kept at the New York Zoological Park. Avicultural Magazine 82: FREILE, J.F., J L. PARRA AND C.H. GRAHAM Distribution and conservation of Grallaria and Grallaricula antpittas (Grallariidae) in Ecuador. Bird Conservation International 20(4): GREENEY, H.F Antpittas and worm-feeders: A match made by evolution? Evidence for a possible commensal foraging relationship between antpittas (Grallariidae) and mammals. Neotropical Biology and Conservation 7(2): Jocotoco Antpitta (Grallaria ridgelyi). Neotropical Birds Online. T.S. Schulenberg, ed. Ithaca, NY: Cornell Lab of Ornithology. Available from: nell.edu/portal/species/overview?p_p_spp

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