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HELODERMA SUSPECTUM (Gila Monster). PREY. Gila Mon-sters are specialized nest predators; their diet includes eggs ofground-nesting birds and reptiles, and juvenile mammals (e.g.,Ammospermophilus leucurus, Neotoma albigula, and Sylvilagusaudubonii; Beck 2005. Biology of Gila Monsters and Beaded Liz-ards. University of California Press, Berkeley. 247 pp.). Here, wereport prey not previously known for H. suspectum, Desert Kan-garoo Rats (Dipodomys deserti). We describe predation episodeson juvenile kangaroo rats in the field, and we document adult kan-garoo rat rescue of nestlings from H. suspectum predation.

We radio-tracked H. suspectum from March 2000 to August 2004at a Mojave Desert site near Lake Mead, Nevada (36.5°N, 114.5°W;elev. 600 m; Gienger 2003. Natural History of the Gila Monster inNevada. Unpubl. MSc Thesis. Univ. of Nevada, Reno. 55 pp.).We located each lizard 2–4 times per day during the active season(March–October). When we found H. suspectum surface active,we followed each lizard from a distance of 5–10 m to record suc-cessful foraging bouts and specific prey.

At 0710 h on 30 May 2003, we observed an adult female H.suspectum excavating an entrance to a rodent burrow complex atthe base of a sandy mound (Fig. 1a). After 2 min of excavation,the H. suspectum disappeared into the burrow and an adult kanga-roo rat ran out of a hole on the other side of the sand mound.Immediately, two altricial (eyes still closed) kangaroo rat pupswere observed trying to crawl out of the burrow. The H. suspectumthen emerged from the burrow behind the pups (Fig. 1b) and seizedone pup by the mid-body. After consuming the first pup, alongwith considerable sand, the Gila Monster then exited the burrow,seized the second pup by the head (Fig. 1c), and consumed it aswell.

At 0758 h on 19 June 2003, we observed the same female H.suspectum excavating a rodent burrow. After digging for ca. 1 min,the burrow collapsed on itself and the lizard disappeared inside.An adult Desert Kangaroo Rat then sprinted out of a second bur-row entrance 70 cm from the collapsed entrance. Three juvenileDesert Kangaroo Rats (pre-weening age; eyes still closed) becamevisible at the second entrance of the collapsed burrow, with onepup attempting to crawl out of the burrow. The adult Desert Kan-garoo Rat (presumably the mother) returned to the opening of thesecond burrow (Fig. 2a), grabbed the pup that was outside of theburrow (Fig. 2b) and carried it to a third burrow opening located3.5 m away from the second (Fig. 2c). The mother then stood out-

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FIG. 1. Excavation and consumption of a nest of kangaroo rats(Dipodomys sp.) by a foraging Gila Monster.

FIG. 2 (opposite). Sequence showing adult female Desert KangarooRat (Dipodomys deserti) attempting to rescue her pups from predation bya Gila Monster. The Gila Monster is inside the burrow and the motherremoves one of the pups before it can be eaten.

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side the third burrow and began a foot-drumming display (Kenagy1976. J. Mammal. 57:781–785; Randall and Matocq 1997. Behav.Ecol. 8:404–413.) in which she rapidly and repeatedly beat herfeet against the sand.

The remaining pups inside the second burrow were squeaking,and the mother returned and moved quickly into the burrow withboth the remaining two visible pups and the H. suspectum. At 0807h, the mother emerged from the second burrow (without any pups)and moved over to the third burrow where she had left the rescuedpup. At 0820 h, the mother left the third burrow without her pupand moved out of sight. For 20 min, the H. suspectum remainedinside the second burrow. At 0840 h, squeaking noises emanatedfrom the third burrow where the Desert Kangaroo Rat mother hadplaced the rescued pup. The Gila Monster remained undergroundin the second burrow until 0923 h, and then emerged from theburrow (Fig. 2d) and walked to, and into, the third burrow, whereit presumably consumed the rescued pup. The H. suspectum re-mained inside the third burrow for ca. 30 min and then emergedabove ground. After walking a few steps, the H. suspectum lickedits face and arched its back with snout pointed upward, a postureGila Monsters often assume after eating large meals (pers. obs.;Beck 2005, op. cit.). This arching posture may help force fooditems down into the stomach, especially when the stomach is al-ready full.

We were also able to verify nest predation by three other GilaMonsters on kangaroo rats at this Nevada site on four additionaloccasions. Each time, we were able to verify the genus of the prey(Dipodomys) by observing adults leaving the nest or pups attempt-ing to crawl out of the burrow. Most of the time we were not ableto identify Dipodomys to species, as the adults fled the nest once itwas discovered, and Gila Monsters immediately consumed thepups. The possible kangaroo rat species in this area include D.deserti and D. merriami (Hall 1946. Mammals of Nevada. Uni-versity of California Press, Berkeley. 710 pp.), but because theseobservations were made as part of a larger natural history study ofNevada H. suspectum, we did not interfere with lizard foragingactivities to determine which of the two Dipodomys species wereinvolved. However, the observation of 19 June 2003 is undoubt-edly a nest of D. deserti, as the kangaroo rat we observed waslarge and had white hairs on the terminal end of its tail (D. merriamiare smaller and have black terminal tail hairs).

These six observations suggest that kangaroo rats can consti-tute an important part of the diet for certain populations of GilaMonsters. Our study site had a considerable amount of sand dunesand Creosote Bush (Larrea tridentata), both of which are appro-priate habitat elements for Dipodomys (Longland and Price 1991.Ecology 72:2261–2273; Schroder 1987. Ecology 68:1071–1083).Most previous ecological studies of Gila Monsters have been con-ducted at sites lacking sand dunes (Beck 2005, op. cit.), henceDipodomys might not be available prey to those populations. Ad-ditionally, our Nevada study site lacks conspicuous populationsof Desert Cottontail Rabbits (S. audubonii), which constitute themost common food item at other study populations of Gila Mon-sters (populations in Arizona and Utah; Beck 2005, op. cit.).

We thank Ned Dochtermann and Kellie Kuhn for reading earlydrafts of the manuscript. The Clark County (Nevada) Multi-spe-cies Habitat Conservation Program and the Biological ResourcesResearch Center at UNR provided funding.

Submitted by C. M. GIENGER and C. RICHARD TRACY,Program in Ecology, Evolution, and Conservation Biology, De-partment of Biology, University of Nevada, Reno, Reno, Nevada89557, USA (e-mail [CMG]: gienger@biodiversity.unr.edu).