Role of reptiles and arthropods in the diet of coyotes in extreme desert areas of northern Mexico




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Role of reptiles and arthropods in the diet of coyotes in extreme desert areas of northern Mexico


L. Hernandez*, M. Deibest & F. Hiraldot
* Instituro de EcologIa, Apcio. Postal 632, 34100 Durango, Dgo., Mexico

t Esracion Biolôgica de Donana, CSIC,Apdo. Postal 1056, 41080 Sevilla, Spain
(

The food habits of coyotes (Canis latrans) during autumn in the Mapimf Biosphere Reserve (southern Chihuahuan Desert) and the Pinacate region (Sonoran Desert) of northern Mexico have been studied through the analysis of

117 and 233 faecal scats, respectively. The main foods of coyotes in both areas were leporids and rodents. Reptiles and arthropods were constrnwd rather often in the more arid Pinacate region, but scarcely at all in MapimI, while the contrary occurred with fruits. The results from Pinacate represent the highest occurrence of reptiles and one of the highest occurrences ever of arthropods previously detected in coyote scats. By considering the diets of some other vertebrate predators in different world deserts, we sptc.xtatt that a high tok of reptiles and arthropods as prey would be a characteristic feature of the vertebrate trophic webs in hot desert environments.

Introduction


The habits of coyotes Canis latrans are among the best known of those of all carnivores (Bekoff, 1982). Nevertheless, information about coyote ecology in the southern portion of its range is scarce. Studies on coyote diet in Mexico have been conducted in cattle ranches of Chihuahua, where the main food was carrion (Perez GutiCrrez eta!., 1982; Vela, 1985) and in pine-oak forests of the Sierra Madre Occidental, where the spring—summer staple prey were rodents, arthropods and berries (Delibes eta!., 1989). Furthermore, most of the ecological research on coyotes has been conducted in productive areas, where they are usually considered as a pest (Voigt & Berg, 1987). Thus, studies in desert areas are lacking and are of special interest, as the faunal composition and the trophic relationships in these ecosystems have many peculiarities (see Cloudsley-Thompson, 1976; Macmahon &

Wagner, 1985; Donázar a a!., 1989). In this paper we compare the foods of coyotes in

autumn in two areas of Mexico differing in their degree of aridity: the Bolsdn de Mapimi

area of the Chihuahuan Desert and the Pinacate area of the Sonoran Desert.

Study areas


The areas investigated were the MapimI Biosphere Reserve (MBR) and the Pinacate region (PR) (Fig. 1). The MBR is located in the Mapimf Bolsón area of the Chihuahuan Desert, in the vertex of the Mexican states of Chihuahua, Coahuila, and Durango (approximately 26°40’N, 103°45’W). It is a level plain with an average altitude of about

Figure 1. Map of Mexico showing the locations of the study areas.

1100 m and discontinuous hills reaching 1350 m. Average monthly temperature ranges from 12 to 28°C and the mean annual rainfall is 263mm (Cornet, 1988). The vegetation is dominated by creosote bush (Larrea tridentata), mesquite (Prosopis glandulosa), prickly- pear (Opuntia sp.), and agave (Agave sp.) and allows a small amount of cattle ranching. The PR is located in the north-west of the state of Sonora, on the northern coast of the Gulf of California (approx. 31°48‘N, 113°30’W), and it is a part of the Gran Desierto of Altar, one of the most arid zones of the world. The study was conducted at the foot of the Pinacate volcanos, where average altitude was under 100 m, mean monthly temperature from 10 to

30°C, and mean annual rainfall approximately 50mm (Ezcurra & Rodrfguez, 1985). The sparse vegetation is dominated by creosote bush and ragweeds (Ambrosia sp.) and does not allow exploitation.

Methods
We collected 233 coyote scats in the PR in November 1982 and 117 coyote scats in the MBR in the autumn (September—November) period of 1985 and 1986. Faeces were identified by size, odour and the nearby presence of coyote tracks. Prey hems were recognized by comparison with reference collections of hairs, teeth, bones, seeds, etc. Results are expressed as the number of occurrences and the per cent occurrence (number of occurrences x 100/number of scats). This method does not accurately reflect the weight


of ingested material, but it is usually considered as giving a good representation of food habits (Erlinge, 1968; Niebauer & Rongstad, 1977). Field abundance of leporids (mainly Lepus californicus but also Sylvilagus auduboni) was determined by road counts from a car by Serrano & Sosa(1985)in the MBR and by ourselves in the PR. Through a contingency- table analysis (0-test, SokaL & Rohlf, 1981) we determined differences in the utilization of each food item between the two areas. The Shannon’s index (H’) was used to estimate trophic diversity (Margalef, 1957).

Results
Coyote diet varied significantly between areas (0= 2088, p < WOO1, df = 14), with a narrower food spectrum in MBR than in PR (trophic diversity H’ = P79 and P94, respectively).

As in many other areas (Bekoff, 1982) the main food of coyotes in both deserts were mammals, especially leporids and rodents (Table 1). Leporids were largely consumed in both localities, but especially in the MER. This agreed with their abundance on each area, as we counted 0-17 individuals per km of road in the PR, and Serrano & Sosa (1985) reported between 2- and 10-fold more (W4—1-8 ind. km’) in the MBR.

Rodents occurred in 38 and 78% of the scats in the MBR and PR, respectively. Among rodents, woodrats (Neotoma sp.) predominated in the MBR, while kangaroo rats



(Dipodomys sp.) and secondarily pocket gophers (Thomomys sp.) were important food


Table 1. Number of occurrence (and per cent occurrence) offood items in the coyote scats of the Mapimi Biosphere Reserve (MBR) and Pinacate region (PR)
MBR PR Gvaluesf

Number of scats



(117)

(223)





Mammals

Ungulates




3 (2-6)


2 (0-8)


2.7**

Leporids

62 (53)

106 (455)

11.2**

Spermophilussp.

Neotomasp.

4 (Th4)

16 (137)


7 (3)

4 (P7)

07

26.4**


Thomomyssp.

0 (0)

41 (176)

231**

Dipodomyssp.

10 (85)

110 (47-2)

22.7**

Perognathussp.

8(68)

4(P7)

9.1*

Peromyscussp.

Unidentifiedrodents

6 (51)

1 (0-8)

6(2-6)

11 (4-7)

34

2-3

Birds

3(2-6)

16 (fr9)

1-0

(Totaireptiles) Sauna Crotalussp.

2 (P7)

1 (0-8)


0(0)

54(23-2)

27 (11-6)

9(3-9)


19.4**

9.8*

5-2

Unidentified Ophidia

0 (0)

10 (43)

51

Unidentified reptiles

1 (0-8)

8(34)

11

Arthropods

0 (0)

46 (19-)

26i**

Fruits

22 (18-8)

0 (0)

60.6**

Otherniaterials

1 (0-8)

2 (0-9)

0-1

t G values indicate differences between areas in the proportion of consumed items.

*p.cQ.Q1. **p.
items in the PR. Differences for these species (and also for pocket mice Perognathus sp., occurring more often in the MER) were statistically significant. The number of seats containing squirrels (Spermophilus sp.) and white-footed mice (Peromyscus sp.) were low in both areas and did not differ statistically (Table 1).

Reptiles and arthropods were eonsumtd rather more often in the P1k, but scarcely or not at all in the MBR. By contrast, fruits were consumed in the MBR and not in the PR. In all cases, the differences were highly significant (Table 1). In the PR, snakes (including nine Croralus) occurred in 19 seats, lizards in 27, and unidentified reptiles in eight. In the MBR we only detected reptiles in two scats (Table 1). Arthropod remains were also a usual component of coyote scats in the PR. Most of the samples included imagos of Coleoptera

(21 scars), while others had larvae (12; mainly of Coleoptera and Lepidoptera) and scorpions (9). On some occasions Orthoptera reach very high densities in the MBR and coyotes include them in their diet (authors, unpubi.), but we did not detect any arthropods in the MBR autumn scats analysed. Vegetative items (excluding some occasional grasses) occurring in the seats of MBR included remains of prickly-pear and mesquite fruits (10 and eight stats respectively). Birds, ungulates (cattle and deer, probably carrion) and garbage occurred in low proportion in both areas and did not differ statistically between them (Table I).

Discussion


The remarkable role of Iagomorphs in the diet of coyotes in both deserts, despite their different abundance, suggests that they are selected by coyotes as a preferred prey. The importance of leporids to many coyote populations has been documented by Clark (1972) and Johnson & Hansen (1979), among others. Additionally, Short (1979) presented evidence that leporids were the main food item for coyotes in an area oI Arizona which is rather similar to the PR.

Rodents were probably consumed in proportion to their availability; whereas bipedal

kangaroo rats are more abundant in the Sonoran Desert, where rainfall and plant cover are very low, while quadrupedal rodents (Neoroma sp., Peromyscus sp.) are more common

in the less arid region of the Chihuahuan Desert (see Kotler, 1984; A. Gonzalez, pers. comm.). A high occurrence of leporids and rodents and a low occurrence of ungulates are

cited in some other studies of coyote food habits in semi-arid regions of the U.S.A. (Johnson & Hansen, 1979; Short, 1979; Andelt, 1985).

Som& of our results could be indicative of certain latitudinal trends in the feeding of

coyotes. So, Knowlton (in Voigt & Berg, 1987) reported a general north to south increase in the availability of small prey in North America. However, we think that some of the trends detected reveal mainly the general features of predation by vertebrates in hot arid environments. This may explain the high proportion of reptiles and arthropods in coyote diet in the PR.

To our knowledge, the results in the PR represent the highest occurrence of reptiles ever previously detected in coyote scats. Young (1951) referred to the occurrence of ‘fish, frogs and reptiles’ in only 116 out of more than 50,000 coyote stomach contents analysed (approx. 02%) while Bekoff (1982) and Voigt & Berg (1987) did not refer to reptiles as prey of coyotes in their revisions of the species ecology. In the same way, reptiles occurred in about 10% of the seats of the black-backed jackal (Canis mesomelas) and in 12% of those of the Cape fox (Vulpes chama) in the Namib Desert (Bothma a al., 1984). They are cited as a common prey of almost all the canids in the Sahara Desert (Le Berre, 1990), while it is difficult to find reptiles as the prey of canids in more mesic environments. When comparing the food habits of the eagle owl Bubo bubo and the great homed owl Bubo virginianus in different Palearctic and Nearctic biomes, however, Donázar a al. (1989) related their diets in deserts to the presence of reptiles and arthropods as prey. Moreover, in a pioneer study on the ecology of the Saharan birds5 Valverde (1957) referred to the


important role of reptiles as the food of the diurnal and nocturnal birdsof prey, staring that

‘in hot climates, vegetarian reptiles play the same role as prey of carnivores than rodents in

cold climates’.

The relevant ecological function of reptiles in hot desert foodwebs is possible because of the high species density and abundance of reptiles in these areas, due to the increased insolation (Schall & Pianka, 1978) and the high production efficiency of small ectotherms

under these environmental conditions (Turner at al., 1976).

Arthropods are also an important component of desert faunas [for instance, in the Negev

Desert, density biomass of isopods is 400 times that of hares (Lapin europaeus) and 14 times that of jerboas (Jaculusfaculus) (Steinberger, 1991)] and a relevant prey group for desert predators. So, two canids in the Namib Desert (the aardwolf, Proteles cristatus, and the bat-eared fox, Otocyon megalotis) are specialized for the consumption of insects, while Scorpionidae are usually consumed by other canid species (Bothma at at., 1984). As indicated previously, both species of great owls (Bubo bubo and B. virginianus) often capture arthropods in the Palaearctic and Nearctic deserts (Donäzar at at., 1989). Valverde (1957) also found invertebrates (mainly Tenebrionidae and Acrididae) to be common prey of the Saharan carnivores, from foxes (Vulpes spp.) to hyaenas (Hyaena brunnea). By contrast, in the analysis of more than 50,000 coyote stomachs from California, Young (1951) referred to the presence of invertebrates only in about P1% of the samples. In the same way, scarcity of fruit in the diet of the Pinacate coyotes could be typical of extreme deserts, although Valverde (1957) reported a fruit (Rhus typartirum) as the May—June staple food of jackals (Canis aureus) in some areas of the Sahara.

In conclusion, we think that some of the differences detected in the diet of coyotes in MapimI and Pinacate, especially the major role of reptiles and invertebrates as prey, and probably the low importance of fruit and the high trophic diversity, may be characteristic features of the trophic webs in the most arid hot ecosystems, which therefore have longer food chains than usually thought.


The study was supported by the Instituto de Ecologla A.C. (projects ‘Mapimf’ and ‘Pinacate’) and through an agreement between the Spanish CSIC and the Mexican CONACYT for research on Biological Reserves. A. L. Herrera, A. Herrera, F. Herrera, R. RuIz de Esparza, F. Pizarro, N. Bustamante and B. Ezcurra helped us in many ways.

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