Status of an endangered subspecies: the peninsular pronghorn at

Status of an endangered subspecies: the peninsular
pronghorn at Baja CaLifornia
Jorge Cancino*, Alfiedo Ortega-Rubio* & José A. Sanchez-Pachecot
*Cenno de Investigaciones Biológicas del Noroeste S. C., Apdo. Postal No.
128, La Paz, 23000, BCS, México
fSEDESOL, Guerrero Negm, Dornicillo Conocido, casa de La Fauna
Guewnr, Negm, B. C.S., M k o
During November 1993, wc travmKd by ground and by air the Vucaino
Desert, the last redoubt of the peninsular pronghom (Anharpra ammkww
penmnrhris). A totd of 29 h of aerid census was performed and a total of 1900
km2 werc covercd by ground, totalling 400 man hours of swey. At pment
the peninsular pronghom population consista of 175 individuais, and inhabits
an area of approxlrnatcly 5000 km2. Because of the impossibility of
controlling its activities o v a such an arca and because of the pment srnall
popuiation size, we propose to msnagc pan of the population in semicaptivity at Mesa de la Choya island, with the objective of assuring the
survival of this subspecies, the most cndangcred mamrnal in Mexico.
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Keyworb Antüocapm amkana penincuhris, Baja California; Peninsular
Pronghom; MCxico; Vucaino Dcsm
The peninsular pronghom (~ña~ocapra
americana peninrularis) is the last pronghom
subspecies to be describcd (Nelson, 1912), and at present is the most endangered
mammal subspecies in Mexico (IUCN, 1988; Diario Oficial, 1991). The origPnal
dismbution of the peninsular pronghom included nearly the whole Baja California
peninsula (Hall, 1981). Human population increases, land development and poaching
have been the main causes of its range reducrion and decline in numbers (GonzálezRomero et d., 1991). Nelson (1925) reponed an estimated population of 500
peninsular pronghoms. In 1959, Leopold (1985), considering just two aseas of
dismbuaon, the Vizcaíno Desert and San Felipe Bay, pointed out a serious decline,
which was even more conspicuous by 1964 (Huey, 1964). 1x1 spite of pronghom
hunting being forbidden since 1922, their dismbution is now resmcted to the Vicaíno
Desert Biosphere Reserve (Diario Oficial, 1988). Even with a Recovery Plan from
government agencies operating since the 1980s (SEDUE, 1986), according to
Jaramillo (1989) and Gonzáíu-Romero et d. (1991) numben have fallen to
approximately 100 individuals. This paper reports the result of the November 1993
0140-1963/96/040463
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census, with the highest number counted since 1977. Information in censuses ftom
1977 to 1993 is summarized, and management of pan of the population as an urgent
measure for recovery of the subspecies is proposed.
Materials and methods
As pan of the Federal and State activities for proteaion for this subspecies (SEDUE,
1986), aenal and terresmal surveys were carried out during 15-20 November 1993 in
the Vizcaino Desert (Fig. 1). Aenal survey was undertaken with a Cessna 182 plane
with one pilot and two observers; we Aew in west-east mnsects at an average height
of 100 m, with 1000 m between transects. Terresuial surveys were camed out by three
ground teams. Each ground team induded one vehicle with two observers, each
equipped with 10 X 50 binoculars. S w e y s began at 0600h, driving the vehides ftom
north to south at an average speed of 60km h-', and ended each day at 1900h.
A total of 200 aenal transects was perfonned in 29 h of flight, covering an area of
approximately 3000 km2. The terrestrial survey covered 1900 km2. Each observation
of pronghorns was recorded with date, time of day, size group, sex and age
composition, location on maps (1 :100,000) (Crumpton, 1991) and direction of íiight.
Location from the airplane was obtained with a Global Positioning System instrurnent.
Both ground and aenal records were plotted, conuasted, and analvsed separately to
avoid double counts.
The total number of pronghoms observed were 117 and 151 individuals, for the
ground and aerial surveys, respeaively (Table 1). The ratios of males to females were
66: 100 for the ground suntey and 140: 100 for the aerial suntey. The total of both
survevs, discounting double counts, was 175 individuals, with a male to female ratio of
85: 100 (Table 1). The results for sex and age composition of the peninsular pronghom
population were 48 adult males, 56 adult femaies, and 7 1 undetermmed (Fig. 2). It is
irnportant to emphasize that such a population size is the maximum recorded since
1925 (Nelson, 1925; Jaramillo, 1989; González-Romero et d.,1991).
Such a population size for the peninsular pronghom enables us to propose some
management practices which were not practicable with a smaller population size, since
they involved the capture of several individuals. Because of poaching and the
possibility of catasuophic changes, such as severe drought, in the factors that support
the present population, we propose to capnire 30 adult individuals: 12 males and 18
females. The capture of su& individuals will be perfonned with two objectives: (i) to
mark with radio-transmitters 10 maie and 10 female individuals, and (ii) to maintain
in semi-captivity two males and eight females at La Mesa de la Choya island (Fig.
1).
Marking individuals with radio-transmitters will be ve. helpful in following the
seasonal movements of the population, a key factor in understanding the ecology and
biology of the subspecies. Evidence exists that indicate irnportant seasonal population
movements, for instance when more than one census has been camed out in the same
year, the summer figures are lower than during any other season Uaramillo, 1989).
Since the same zones were searched in those censuses at diñerent seasons, the
pronghoms must have moved to unknown places during the sumrner.
We are certain that a radio-mcking snidy would be useful in establishing the precise
dismbution and seasonal movements of the population. Expenence and severa1
options are already available (O'Gara & Yoakum, 1992).
Mesa de la Choya is an artificial island fonned by the development of an evaporation
STATiJS OF THE P E N I N S W PRONGHORN
465
basin for sait production. Its area is approximately 10,000 ha, with controlled access.
We can be sure that the main pronghorn population will be able to reproduce
successfully, as the size of the population will still be above the minimum population
previously reponed (Jaramillo, 1989; Gonzalez-Romero et al., 199 1) .
However, if the main population in freedorn is exterminated by uncontrolled
hunting, other human-related causes, or by any environmentai catastrophe, the
\, Ay-
-<;
\
IQ
Oio de Liebre
,
/
Figure 1. Location of the Vucaino Desert and La Mesa de la Choya island.
Table l. Results of some surveys on the Peninsular Pronghorn
population at the Vizcaino Desert, Baja California Sur, ~Mexico,
1977-1 993. (A=aenal census; S=ground survey)
Year
IMonth
-
Survey type
Toca1 countrd
.Maie:female
Source*
---
1977
1982
1988
1993
Feb
Jan
.Mar
Nov
S
S
S
AS
83
39
48
175
97: 100
69: 100
65:lOO
85: 100
(1)
(1)
(3)
This paper
*(l)Jaramillo(1989);(7) Gonzalez-Romero ct d. (190 1).
Figure 2. Sex and age composition data of the Peninsular pronghorn population, November
1993. (3= males; IJ = females; = undetermined).
survival of the endemic subspecies will be assured by the protected population on the
Mesa de la Choya island.
This 5mdy was carried out wirh the support of the Centro de Investigaciones Biológicas del
Soroesre (CIBSOR), the Consejo Nacional de Ciencia y Tccnoltiqía (COSACyT) projrct So.
0639x91 10, the Delegación Estatal at Baja Califomia Sur of the Secretaria de Desarrt,llo Social
(SEDESOL) and the Compariia Esporradora de Sal íESSA'i. We would like rn rhank Professor
John Cloudsley-Thompson and one anonymous referee for their suggestions which improved
earlier versions of this manuscnpt. We rhank Sandra Lanham (Environmental Fiying Services)
for her excellent piloting.
-
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