Predation on Caecilians (Caecilia Orientalis) by from the Nest, on the Opposite Side of a Stream

Home , Barred hawk, Caecilia, Caecilian, Caecilia orientalis, Dermophis, Dermophis mexicanus

ment, and thus are listed as “Data Deficient” by the IUCN (2006). Perhaps because of their elusive nature, there is an increasing in- terest in the biology of caecilians (Kupfer et al. 2006; Measey and Herrel 2006). Predator-prey interactions are widely recognized to have important effects on population dynamics (e.g., Krebs et al. 1995; Lotka 1925; Volterra 1926), but in the case of caecilians, little is even known about which taxa act as predators. Snakes are consid- ered the main predators of caecilians (Duellman and Trueb 1994; Kupfer et al. 2003), although some other predators such as turtles (Zamprogno and Zamprogno 1998), spiders (Boistel and Pauwels 2002), and ants (Measey 2004) have been documented preying on caecilians. Identifying predators of amphibians is important in the context of amphibian declines, because predation may tip already declining populations over the edge toward extinction (Corn 1993; Parker et al. 2000). Here we show that a tropical hawk acts as an important predator of the caecilian Caecilia orientalis and that this unexpected ecological interaction depends strongly on weather. Methods.—We filmed a Barred Hawk (Leucopternis princeps) nest using a hidden camera from 15 February–8 May 2004 and 7– 28 January 2005 for a total of 599 h in the private reserve of Cabañas San Isidro, next to Yanayacu Biological Station (00°35'S, 77°53'W; 1950 m elev.). During most days of filming, the nest was filmed continuously during daylight hours (from morning to evening) when the hawks were active. The Barred Hawk is a rare, large hawk (total length = 52–61 cm) found from northern Peru to Costa Rica (700–2200 m; Ridgely and Greenfield 2001). The 1700 ha reserve comprises a mosaic of primary and secondary growth in humid, montane, evergreen forest about 3 km W of the town of Cosanga in the Napo Province of northeastern Ecuador (for a more complete site description, see Greeney et al. 2006). Each year, the same Barred Hawk pair raised a single chick in Herpetological Review, 2008, 39(2), 162–164. the same nest. The nest was located on a rocky ledge 5 m from a © 2008 by Society for the Study of Amphibians and Reptiles rushing waterfall. The blind was installed 3.5 m above and 10 m Predation on Caecilians (Caecilia orientalis) by from the nest, on the opposite side of a stream. All videos were Barred Hawks (Leucopternis princeps) Depends transcribed at a later date. In addition to recording prey brought to on Rainfall the nest, we recorded whether it rained during each hour-long time interval. Since video quality was excellent, most taxa were clearly identifiable, but seven unknown taxa were excluded from the analy- HAROLD F. GREENEY and sis. Because caecilians surface primarily during heavy rains and RUDY A. GELIS snakes are active at Yanayacu when it is clear and sunny, we hy- Yanayacu Biological Station, Cosanga, Napo, Ecuador pothesized that Barred Hawks would bring more caecilians to the and nest, but fewer snakes, when it was raining. We tested this in 2004 W. CHRIS FUNK using a Fisher’s exact test. This was the second Barred Hawk nest Department of Biology, Colorado State University ever documented (Muela and Valdez 2003) and the first closely Fort Collin, Colorado 80523-1878, USA e-mail: [email protected] monitored to document feeding behavior. Details of the breeding ecology of these Barred Hawks are being prepared separately for Caecilians are limbless, subterranean or aquatic amphibians an ornithological journal (R. A. Gelis and H. F. Greeney, unpubl. found throughout much of the tropics (Duellman and Trueb 1994; ms.). Himstedt 1996). Although amphibians are declining dramatically Results.—To our surprise, a caecilian species (Caecilia (Stuart et al. 2004), the conservation status of caecilians is largely orientalis) was the main prey item brought to the nest by two Barred unknown due to lack of information on their ecology and natural Hawk parents to feed a single chick brooded each year (Fig. 1; history (Gower and Wilkinson 2005). A handful of studies have videos available upon request). Caecilia orientalis is a large cae- documented caecilian life histories (e.g., Funk et al. 2004; Gans cilian (total length = 31–62.5 cm) found in the Andes of Ecuador 1961; Kupfer et al. 2005; Malonza and Measey 2005; Parker 1936, and Colombia and is the only caecilian known from this site (Funk 1958; Sanderson 1937; Sarasin and Sarasin 1887–1890; Taylor et al. 2004; IUCN 2006). Prey items delivered to nestlings included 1968; Wake 1980). Nevertheless, 114 out of 172 species (66%) of 50 caecilians (48.1% of diet), 36 snakes (34.6%; Atractus caecilians remain too poorly known for an accurate status assess- occipitoalbus and two unidentified colubrid species), five giant

162 Herpetological Review 39(2), 2008 consistently find these elusive amphibians. These results suggest that Caecilia orientalis may actually be fairly common, as has been found for some other caecilian species (Measey 2004), yet C. orientalis is reported as “uncommon in Ecuador” by the Global Amphibian Assessment (IUCN 2006). Because of the rarity and huge ranges of Barred Hawks, we were only able to find and in- tensively monitor one pair over two years. It will likely take several years of intensive searching to find additional Barred Hawk nests. Nonetheless, the dominance of caecilians in this pair’s diet and consistent use of these amphibians over two years suggests that caecilian predation by Barred Hawks will likely be widespread at sites with abundant caecilian populations. Rainfall has increased at some sites in Ecuador over the last 40 years (Haylock et al. 2006), although rainfall trends at Yanayacu are unknown. If predation on caecilians is typical for Barred Hawks, changes in rainfall could alter this predator-prey interaction and potentially impact populations of both species. Climate change has already been implicated in amphibian declines in Ecuador and elsewhere in the Neotropics (Blaustein and Dobson 2006; Pounds et al. 2006). Predicting the ecological impacts of climate change, however, will require a better understanding of trophic interactions and the influence of weather on these interactions as documented here. Determining the effect of predators on caecilian populations will also require a much better understanding of caecilian population dynamics. Studying the population ecology of these fossorial amphibians has proven difficult in the past due to low detectability, a paucity of methods for individually marking caecilians, and the rareness of some caecilians species. However, at Yanayacu Bio- logical Station and some other sites (Bustamante 2005; Measey 2004; Péfaur et al. 1987), caecilians can be abundant and thus potentially amenable to study. New methods have also recently been developed for marking caecilians for capture-recapture esti- mation of vital rates and demographic parameters (Gower et al.

FIG. 1. (A) Barred Hawk (Leucopternis princeps) with caecilian 2006; Measey et al. 2001, 2003). Use of these methods in combi- (Caecilia orientalis) in talons (left). The white chick is seen in background nation with population modeling (Biek et al. 2002) and molecular (upper right). A color version of this photo is available upon request. (B) genetic markers (Beebee 2005; Funk et al. 2005) should help illu- Proportion of Barred Hawk diet in 2004 and 2005 composed of different minate the demography, ecology, and conservation status of these taxa. (C) Barred Hawks bring significantly more caecilians than snakes fascinating animals. to the nest when it is raining (P < 0.00001, N = 58). Acknowledgments.—We thank Carmen Bustamante for permission to earthworms (4.8%), three young birds (2.9%), three small mam- conduct research on the San Isidro Reserve. We also thank J. Beatty, L. mals (2.9%), and seven unknown animals (6.7%) (Fig. 1B). Coloma, D. Gower, J. Matthews, J. Measey, and A. Sheldon for com- Caecilia orientalis vouchers from this site are available in the ments on the manuscript. Funding was provided by Matt Kaplan, John V. and Ruth Ann Moore, a Pamela and Alexander F. Skutch Award, and a Museo de Zoología at the Pontificia Universidad Católica del Ec- Declining Amphibian Populations Task Force Seed Grant. This study was uador (QCAZ 21417–21419). conducted in compliance with Ecuadorian laws. This is publication num- As predicted, we found that Barred Hawks brought significantly ber 59 of the Yanayacu Natural History Research Group. more caecilians than snakes to the nest during hour-long time in- tervals when it was raining (Fisher’s exact test, P < 0.00001, N = LITERATURE CITED 58; Fig. 1C). Discussion.—It is surprising that an aerial predator, the Barred BEEBEE, T. J. C. 2005. Conservation genetics of amphibians. Heredity Hawk, was able to find subterranean prey such as caecilians. A 95:423–427. previous report states that birds may occasionally prey on caecil- BIEK, R., W. C. FUNK, B. A. MAXELL, AND L. S. MILLS. 2002. What is missing in amphibian decline research: Insights from ecological sensi- ians (Wake 1983), but this report did not provide specific bird tivity analysis. Conserv. Biol. 16:728–734. species names or details of this predator-prey interaction. During BLAUSTEIN, A. R., AND A. DOBSON. 2006. A message from the frogs. Na- several years of research at Yanayacu, caecilians were rarely en- ture 439:143–144. countered on the surface in the day even when it was raining (Funk BOISTEL, R., AND O. S. G. PAUWELS. 2002. Oscaecilia zweifeli (Zweifel’s et al. 2004). Thus it is unknown how Barred Hawks are able to caecilian). Predation. Herpetol. Rev. 33:120–121.

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