Abstract: the Annual and Seasonal Diet of the Bobcat (Lynx Rufus) Was Determined From

478

Abstract: The annual and seasonal diet of the bobcat (Lynx rufus) was determined from analysis of 188 feces in the Cape region of Baja California, Mexico, an arid zone with numerous subtropical elements in its flora and fauna. Bobcats fed mainly on lagomorphs, which reached 74% of occurrence, followed by rodents (40%), reptiles (15%), and birds (12%). No seasonal variations were observed. The results were consistent with those of studies elsewhere, indicating that bobcats still rely upon lagomorphs for much of their food in southern latitudes. This supports the hypothesis that lynx have evolved to prey on hares and rabbits. The prevalence of reptiles as prey of hohcats in our study area was the highest ever reported. They were reported as bobcat prey in only I of 20 studies from north of latitude 40°, but in 14 of the 18 studies carried out south of this latitude. With regard to feeding on reptiles, the habits of bobcats in Baja California Sur resemble those of other similar-sized felids in tropical areas, such as ocelots (Felis pardalis) and servals (Leptailurus servo!).

Résumé : L’analyse de 188 tbces recueillies dans la region du Cap, en Basse Californie, Mexique, une zone aride comptaot de nombreux éléments sub-tropicaux dans sa faune et sa fore, a permis de determiner les regimes alimentaires annuel et saisonnier du Lynx roux (Lynx rufus) dans la region. Les lynx se nourrissent surtout de lagomorphes, jusqu’b

74% du régime, de rongeurs (40%), de reptiles (15%) et d’oiseaux (12%). Aucune variation saisonnière n’a été enregistrée. Ces résultats concordent avee ceux obtenus en d’autres regions, ce qui semble indiquer que les lynx comptent surtout sur les lagomorphes comme proies aux latitudes australes. Ces données appuient l’hypothèse selon

laquelle le lynx s’est adapté a chasser les lièvres et les lapins. La proportion de reptiles dans le régime alimentaire des

lynx de cette region est Ia plus haute jamais signalée. Des reptiles ont été mentionnés dans le régime alimentairc du

Lynx roux dans seulement l’une des 20 etudes connues au nord du 40° paralléle, mais daos 14 des 18 etudes connues au sud de cette latitude. En cc qui conceroe Ia consommation de reptiles, les habitudes des lynx de la Basse Californie se rapprochent de celles d’autres félins de taille semblable des regions tropicales, l’Ocelot (Felis pardalis) et le Serval (Leptoilurus serval).

[Traduit par la Redaction]

Introduction

Conspecific populations of widely distributed species will encounter geographical differences in the pressures that mold their feeding behavior (Arnold 1981). Hence, we would expect the regional diets of species having wide geographical distri butions to reflect the availability of different prey resources.

The bobcat (Lynx rufus) is the most widely distributed native cat in North America, ranging from southern Canada (approximately 52°N) to southern Mexico (17°N) (Anderson

1987). Its food habits are well known in many parts of this

Received June 7, 1996. Accepted October 7, 1996.

M. Delibes’ and S.C. Zapata. EstaciOn Bioldgica dc Doiiana, Consejo Superior de Investigaciones Cientificas (CS IC), Apartado 1056, Scvilla 41080, Spain.

M.C. Blázquex. Estacidn BiolOgica dc DoAana, CSIC, Apartado 1056, Sevilla 41080, Spain, and Ccntro de

tnvcstigaciones Bioldgicas dcl Norocste, Apartado 128,

La Paz 23000, Mexico.

R. Rodriguez-Estrella. Centro de lnvcstigacioncs BiolOgicas dcl Norocstc, Apartado 128, La Paz 23000, Mexico, and EstaciOn lliológica de DoOana, CSIC, Apartado 1056, Sevilla

41080, Spain.

Author to whom all correspondence should be addressed.

range, and its diet is usually based on lagomorphs (hares and rabbits), although there is some geographical variation, deer and (or) small mammals being important prey in some areas (McCord and Cardoza 1982; Maehr and Brady 1986). Up to nt)w, no information has existed on the food habits of this felid in the southernmost part of its range, which is included in or neighboring the Neotropical region.

The cat species of northern areas seem to be quite special ized in their diet, and Holarctic lynx species (genus Lynx, following Wilson and Recdcr 1993) are thought to have evolved to prey on Iagomorphs (Kurten 1968). ‘l’ropical felids, by contrast, usually take all the vertebrate taxa they can handle, especially reptiles (Emmons 1987; Kitchcner 1991).

This paper reports the annual and seasonal diet of bobcats in the Cape region of Baja California (Mexico), an area with numerous suhtropical elements in its vegetation and fauna (Goldman and Moore 1946). We expected that lagomorphs were important in the diet of Baja California bobcats (as they, like other lynx species, have evolved to capture lagomorphs), but also that reptiles would be more important here than else where (owing to subtropical conditions in the area). To try to detect whether there is a latitudinal gradient in the impor tance of lagomorphs and reptiles as bobcat prey, we review

38 papers concerning the Ibod habits of this species in differ cnt areas.

Delibes el al. 479

Bobcats in Baja California belong to the subspecies Lynx rufus peninsularis and are reported to be the smaNest members of the species (Thomas 1898; Samson 1979). Given the strong relationship between predator and prey sizes (Rosenzweig

1966), especially in feuds (Leyhausen 1965), we expected

this small size to influence the kind of prey taken.

Study area

Fieldwork was conducted in an area of about 10 km2 in and around El Comitán, owned by the Centro de Investigaciones Biológicas del Noroeste. It is a coastal lowland located 17 km north of La Paz City (24°17’N, 110°20’W). Soils are sandy loam, while the xerophytic sarcocaulescent scrub vegetation (Leon de Ia Luz et a!. 1996) is dominated by cardon cacti (Pachycereus pringlel), dagger cacti (Stenocereus gu,n,nosus), mesquites (Prosopis articulara), palo verde trees (ercidiu,n microphyllurn), Adam’s trees (Fouquieria thguem), plum (Cyriocarpa edulis), copales (Bursero spp.), lomboys (Jairopha cinerea), and chollas (Opunüa cholla). This kind of vegetation (“cardonal”) is very characteristic of the best preserved habitats in Baja California Sur. Mean annual rainfall

is 150 mm, with precipiuition concentrated during the summer months, from July to September. Mean annual temperature is 23.9°C.

Methods

We collected bobcat feces (n 188) during 1994 by walking peri odically along sandy paths and dry riverbeds. At least two females with kittens and some males were known to be living in the area during the study period. All of the area was covered regularly, so we considered the collected feces to be a representative sample of those produced, although some were found in easily recognizable clusters ( toilets” or fecal marking locations; Bailey 1972). Feces were separated, labeled, and dried at 60°C until they reached a constant dry mass. If possible, prey items were identified to species by comparing hairs, teeth, feathers, scales, and bones with a refer ence collection. Results are presented as frequency of occurrence (number of occurrences of each prey type x 100 divided by the number of fecal samples; this implies that the sum of frequencies may be above 100). This method does not accurately reflect the mass of ingested material (e.g., Weaver 1993), but it is usually con sidered to give a good representation of food habits (Corbett 1989). Samples were divided into four, according to season: winter (January—March), spring (April—June), summer (July—September), and autumn (October—December). Numbers of occurrences were compared among samples through a contingency-table analysis (G test; Sokal and Rohlf 1981).

Results

Prey items in bobcat feces from Baja California Sur included at least 9 species of mammals, 7 birds, 5 reptiles, and 1 arthro pod (Table 1). The most important prey category was lago morphs, which occurred in 73.9% of the feces. Rodents were the second most important component of the diet, as they occurred in 40. 1 % of the feces. Reptiles ranked third in importance (15.4% in occurrence), followed by birds (12.2%). Scorpions were also found.

In the study area the predominani prey of the bobcat were the jackrahbit and cottontail rabbit, consumed in about the same proportions. The pocket mouse was the most frequently

consumed rodent, followed by the white-tooted mouse and desert wood rat. The California quail was the most frequent bird in the analyzed feces. Among reptiles, the spiny-tailed iguana was the predominant prey species. It ranked fourth in occurrence, exceeded only by the two leporids and the pocket mouse (Table 1).

No significant seasonal changes in prey composition were detected: bobcats fed primarily on rabbits and secondarily on rodents in all seasons (Table 1). This lack of seasonal change in diet suggests that prey abundance and vulnerability do not vary greatly during the year, which is characteristic of tropi cal environments.

Discussion

Lagomorphs occurred in most of the seats, with little varia tion between seasons, indicating that bobcats still rely upon them for much of their food near the southern limit of their range. This is consistent with the results of most studies of bobcat diets, irrespective of latitude. Lagomorphs occurred in more than 30% of the samples (stomachs and (or) intestine and feces) in 30 (83%) of 36 studies of bobcat diets in areas ranging from 48°N to 24°N (Table 2). Lagomorph remains were present in 49% or more of the samples in almost one- half of these studies. In two cases only, they reached less than 10% occurrence, in each case being replaced by another mammal species, the mountain beaver (Aplodontia rufa; 74% frequency of occurrence versus 7% for lagomorphs in 247 feces from Oregon; Witmer and deCalesta 1986) and white- tailed deer (79% of occurrence in 43 feces collected during the winter in Massachussetts, with only traces of leporids, being found; McCord 1974).

These results support Kurten‘s (1968) hypothesis concern

ing the evolution of the feeding specialization of lynx species on lagomorphs. Nevertheless, rodents seem to be more impor tant than rabbits as food of bobcats in the southern Appala chians and western United States, and deer are also a notable prey of bobcats in the northeastern United States (Machr and Brady 1986).

Besides the fact that bobcats depend upon lagomorphs even at subtropical latitudes, the most distinctive feature in the diet of bobcats in Baja California is the high frequency of occurrence of reptiles, which appeared in more than 15% of the feces. The reptiles included at least two species of iguanas and three species of snakes, one of them venomous (Table 1). Both of the iguanas are relatively large, reaching 300 g in the case of the spiny-tailed iguana. These were consumed also in winter, in spite of the fact that they have a short hibernation period in the area (Blázqucz and Ortcga-Ruhio 1996).

Predation on reptiles by bobcats has been considered unusual elsewhere. In the review by Anderson (1987), reptiles were not even referred to as an occasional prey of the spe cies, while in the reviews by McCord and Cardoza (1982) and Rolley (1987), it is stated that bobcats cat mammals and some birds, although in certain circumstances they can take almost anything available, including reptiles.

Approximately 40% of the studies reviewed reported one

or more reptiles as prey of the bobcat (Table 2), including snakes (51.4% of all identified reptiles; most were non- venomous) aiid lizards (48.6%). The frequency of occurrence

Cc) t997 NRC Canada

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Can. J. Zool, Vol. 75, 1997

Table 1. Seasonal diet (numbers of prey items) of bobcats from El Comitán, Baja California Sur, through analysis

of feces.

Frequency of occurrence

Total Winter Spring Summer Autumn

(n = 188) (n = 74) (n = 49) (a = 24) (n = 41) G p

Mammals

Lagomorphs

Cottontail (Sylvilagus sp.)

Black-tailed jackrabbit (Lepus californicus)

Unknown lagomorph Total lagomorphs Rodents

Antelope squirrel (Animosperniophilus leucurus)

Pocket gopher (Thoniornys sp.) Pocket mouse (Chaetodipus sp.) Kangaroo rat (Dipodomys merriami) White-footed mouse (Peromyscus sp.) Desert wood rat (Neotoma lepida) Unknown rodent

Total rodents

Others

28.2

26.0

19.7

73.9 76.9 67.3 70.8 78.0 1.919 0.7

1.6

1.0

19.1

3.2

4.7

5.8

40.1 39.0 38.7 41.4 41.4 1.778 0.7

Domestic cat (Fells catus)

Total mammals

Birds

American kestrel (Falco spa rverius California quail (Callipepla calfornica) White-winged dove (Zenaida asiatica) Ground dove (Columbina passe rina) Common flicker (Colaptes auratus) Flycatcher (Myiarchus sp.)

Thrasher (Toxostoma sp.) Unknown bird

0.5

96.8

0.5

4.2

1.1

1.6

0.5

2.1

1.3 0 0 0 —

95.9 97.9 91.6 100 1.787 0.7

Total birds

Reptiles

Desert iguana (Dipsosaurus dorsalis)

Spiny-tailed iguana (Ctenosaura hemilopha)

Unknown lizard

Whipsnake (Masticophis flagellum) Gopher snake (Pituophis melanoleucus) Speckled rattlesnake (Crotalus mitchelli) Unknown snake

Total reptiles

Arachnida

Scorpion

Note: vi is the number of feces examined.

of reptiles ranged between 0 and 15.4% (this study), hut rarely exceeded 2%. A definite north to south trend was not detected, but reptiles were reported as bobcat prey in only I of 20 studies carried out north of 40N, but in 14 of 18 studies carried out south of this latitude (Table 2).

North to south differences in predation upon reptiles could he related to changes in reptile abundance and the distribu ti()n of reptile sizes. A high incidence of reptiles in the diet of predators has been reported in desert areas at low lati tudes. In a pioneer study on the ecology of Saharan birds, Valverde (1957) stated that “in hot climates, vegetarian rep tiles play the same role as prey of carnivores as rodents in

12.2 8.1 22.4 4.2 12.5 4.519 0.2

2.1

5.3

1.6

1.1

2.1

1.1

2.1

15.4 21.0 12.6 16.7 9.7 2.802 0.4

1.1 0 0 0 4.8

cooler climates.” Likewise, Hernández et al. (1994) reported the importance of reptiles and insects in the diet of coyotes (canis lutrans) living in the arid Sonoran desert, and other authors (e.g., Bothma et al. 1984) have also reported earn iVCOS feeding on reptiles in other deserts. This is possibly due to the high species divcrsity and abundance of reptiles in these areas, because of the increased solar radiation (Schall and Pianka 1978) and the high production effIciency of small ectotherms under these conditions (Turner Cf al. 1976).