Knowledge about the biodiversity of Baja California has been obtained mainly from natural protected areas (NPAs), while some unprotected natural areas have been poorly studied. The Sierra Cucapá in the northeast of the peninsula is one example. The objectives of this study are 1) to integrate existing knowledge of bird, mammal, and reptile diversity in Cucapá from public databases, citizen science platforms, and information generated from fieldwork, 2) to identify the spatial distribution of records in the study area, 3) to compare the composition of vertebrate species of Cucapá with that of NPAs of northern part of the peninsula, and 4) to assess the biological conservation value of Cucapá. We obtained records of 150 species of native vertebrates (102 birds, 34 mammals, and 14 reptiles) of which 10 species of birds, four mammals, and seven reptiles are included in a risk extinction category. The different sources of information contributed in a complementary way to the species inventories. Large areas in western and northern Cucapá lack records. The total difference in species composition between Cucapá and nearby NPAs ranged between 58 and 69% for birds, 61 and 79% for mammals, and 69 and 87% for reptiles. The species richness of Cucapá, its particular species composition, the presence of species in risk extinction categories, and the number and size of unexplored areas indicate that this area represents an opportunity for biological conservation in the northern part of the Peninsula. This work provides compelling data for the protection of Cucapá.

citizen science, databases, fieldwork, natural protected areas system, species composition

The Baja California Peninsula (hereafter the Peninsula) in northwestern Mexico is a biologically important region with a remarkable species richness and high amount of endemism in various biological groups (Rojas-Soto et al. 2003; Riemann and Ezcurra 2005; Ramírez-Acosta et al. 2012). For example, 514 species of birds (Erickson et al. 2013), 70 mammals (Guevara-Carrizales et al. 2016), and 99 reptiles (Hollingsworth et al. 2015) have been recorded. However, biological diversity on the Peninsula has been evaluated mostly in natural protected areas (NPAs), with gaps in or knowledge of species richness especially in non-protected areas.

The NPAs system in the northern part of the Peninsula includes eight areas covering two main ecosystems types: arid environments under 100 m above sea level (a.s.l.) in the extreme northeast, and coniferous forests between 1500 and 1900 m a.s.l. in the Sierra de Juárez. Biological information on certain groups of terrestrial vertebrates is available for some of these NPAs under government administration (e.g. CONANP 2007, 2011; Guevara-Carrizales et al. 2013; Hinojosa-Huerta et al. 2013). However, some NPAs under community or private management, as well as unprotected natural areas, lack species inventories, making difficult to evaluate their potential for biological conservation and consequently limiting the possibility of including unprotected areas in formal protection schemes.

The Sierra Cucapá (hereafter Cucapá) is an unprotected mountainous massif in the northeast of the Peninsula covering 36400 ha and extending approximately 60 km with a northwest–southeast orientation. Cucapá is known to harbor endemic species of flora and fauna (Grismer 2002; Webb and Salazar-Ceseña 2011) and is located in the proximity of several NPAs under different types of administration (government, private, and community). However, its biological diversity has not been characterized, and its potential contribution to the biological conservation of the region, or its complementarity to the existing NPAs system, has not been evaluated (Riemann and Ezcurra 2005; Lovich et al. 2009; Martínez et al. 2016). Northeast of Cucapá lies the city of Mexicali with a population > 1 million and considerable agricultural production (http://www.inegi.gob.mx). Furthermore, the region is experiencing a growing industrial activity that includes renewable energy generation (Alemán-Nava et al. 2014). Thus, human activities around Cucapá represent a threat to its biodiversity.

Here we present the first comprehensive summary of the biological diversity of three groups of terrestrial vertebrates in Cucapá and the first analysis of its complementarity to the NPAs system of the northern Peninsula. Our objectives are 1) to integrate existing knowledge of bird, mammal, and reptile diversity in Cucapá combining information from public databases, citizen science platforms, and information generated from fieldwork, 2) to identify the spatial distribution of records into the study area, 3) to compare the species composition of birds, mammals, and reptiles of Cucapá with that of NPAs of northern part of the Peninsula, and 4) to assess the biological conservation value of Cucapá.

We recorded a total of 150 species of vertebrates for Cucapá: 102 species of birds, taxonomically grouped in 15 orders, 38 families and 83 genera; 34 species of mammals, grouped into six orders, 14 families and 26 genera, and 14 species of reptiles, belonging to one order, five families and 12 genera (Tables 1, 2). Additionally, we recorded six species of exotic birds, but we did not include those in the analysis (Table 1). The best-represented families (by number of species) are Passerellidae in birds (11 spp.), Heteromyidae in mammals (eight spp.), and Phrynosomatidae in reptiles (nine spp.). Sixteen, seven, and three bird, mammal, and reptile families, respectively, were represented by a single species (Table 1).

In general, data sources contributed with multiple overlapping species (i.e. same species reported in two or more data sources), but each source also contributed with unique species (Table 1). Of the 102 species of birds, we recorded 79 during fieldwork and 20 of them were observed exclusively with this method; similarly, we obtained records of 23 bird species from GBIF and five were not recorded in any other data source; and citizen science platforms contained records for 76 species, 19 of which were only reported there. In the case of mammals, we recorded 27 species during fieldwork, with 12 of them observed exclusively with field efforts; similarly, GBIF and iNaturalist contained records for 15 and 12 species respectively, five and one of which were only recorded respectively in each platform. For reptiles, five of the 10 species that we identified during fieldwork were not reported in other data source; however, three out of the nine species obtained from GBIF were not reported in any other data source. The four reptile species reported in citizen science platforms from Cucapá were either observed in the field or reported in GBIF.

In terms of number of records and locations, birds are the best represented group in the study area, followed by mammals, while reptiles are the group with the fewest records. The records are located mainly in the south, southeast, and central-west parts of the study area, covering the entire elevation range of Cucapá, while wide high areas with rugged terrain in the western portion, the northern area, and some low and flat areas to the east lack records (Fig. 1).

According to SEMARNAT (2010), 21 of the vertebrate species reported here are included in some risk of extinction category. In the case of birds, two species are Threatened, seven are Subject to Special Protection, and one is Probably Extinct in the Wild. For mammals, two species are Threatened, one is Subject to Special Protection, and one is Endangered. In the case of reptile species, four are Threatened and three are Subject to Special Protection. According to the IUCN Red List, only one species of mammal is Vulnerable (Table 1).

Comparison of species richness and composition with natural protected areas

Bird species richness in Cucapá (102 spp.) is higher than richness in community NPA Rancho Rodeo del Rey (90 spp.), but lower than in the rest of the NPAs. Mammal species richness in Cucapá (34 spp.) is higher than in HDRC (30 spp.) and SHRRC (24 spp.), but lower than in the rest of the NPAs. For reptiles, species richness in Cucapá (14 spp.) was lower than for all NPAs (Table 2). The largest differences in bird species composition were between the community NPA Rodeo del Rey and RBAGC, Constitución de 1857, and Laguna Hanson (β_jac = 0.72 in all cases; Table 3A); for mammal and reptile species, the largest differences were between Laguna Hanson and HDRC (β_jac = 0.81 and 0.89 respectively; Table 3B, C). The lowest total difference in species composition of birds, mammals and reptiles were between Laguna Hanson and Constitución de 1857 NPA (β_jac = 0.08, 0.42 and 0.34, respectively; Table 3A–C).

Table 2.

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Number of orders, families, genera, and species of birds, mammals and reptiles recorded in Sierra Cucapá and six NPAs of northern Baja California: Parque Nacional Constitución de 1857, Reserva de la Biosfera del Alto Golfo de California (RBAGC), Humedales Remanentes del Río Colorado (HDRC), Sistema de Humedales Remanentes del Río Colorado (SHRRC), Laguna Hanson, Rodeo del Rey (community).

NPA/region	Taxonomic group	Orders	Families	Genera	Species
Sierra Cucapá	Birds	15	38	83	102
	Mammals	6	14	26	34
	Reptiles	1	5	12	14
Constitución 1857	Birds	18	45	116	174
	Mammals	8	19	41	63
	Reptiles	1	15	30	48
RBAGC	Birds	22	58	174	320
	Mammals	8	21	42	58
	Reptiles	2	13	32	46
HDRC	Birds	20	50	139	217
	Mammals	7	13	26	30
	Reptiles	2	10	17	21
SHRRC	Birds	20	49	145	241
	Mammals	6	10	18	24
	Reptiles	1	12	25	28
Laguna Hanson	Birds	18	44	110	165
	Mammals	7	15	26	39
	Reptiles	1	12	20	31
Rodeo del Rey (C)	Birds	15	36	68	90

Total differences in species composition (β_jac) between Cucapá and the NPAs ranged between 0.58–0.69 for birds (Table 3A; Fig. 2A), 0.61–0.79 for mammals (Table 3B; Fig. 2B), and 0.69–0.87 for reptiles (Table 3C; Fig. 2C). The differences in species composition between Cucapá and the NPAs were mainly explained by turnover of species in the comparisons with Laguna Hanson, Rodeo del Rey and Constitución 1857, in the case of birds (β_jtu = 0.55, 0.54, 0.53, respectively; Table 3A; Fig. 2A), for mammals in the comparisons with Laguna Hanson, HDRC and SHRRC (β_jtu = 0.62, 0.74, 0.58, respectively; Table 3B; Fig. 2B), and for reptiles in the comparisons with Laguna Hanson, HDRC, SHRRC, and Constitución 1857 (β_jtu = 0.78, 0.67, 0.44 and 0.60, respectively; Table 3C; Fig. 2C). In contrast, the differences in composition were mainly explained by nestedness in the comparisons between Cucapá and HDRC, SHRRC, and RBAGC for birds (β_jne = 0.35, 0.51, 0.63, respectively; Table 3A; Fig. 2A), for mammals in the comparisons between Cucapá with Constitución 1857 and RBAGC (β_jne = 0.48, 0.45 respectively; Table 3B; Fig. 2B) and for reptiles only in the comparison between Cucapá and RBAGC (β_jne = 0.51; Table 3C; Fig. 2C).

Table 3.

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Differences in species composition between pairs of sites. A birds B mammals C reptiles. The values outside the parentheses correspond to the total difference in species composition (β_jac), the first value inside the parentheses indicates the difference due to species turnover (β_jtu) and the second value indicates the proportion due to nestedness (β_jne).

	Sierra Cucapá	Laguna Hanson	HDRC	SHRRC	Const. 1857	RBAGC
A)
Laguna Hanson	0.68 (0.55+0.13)
HDRC	0.63 (0.28+0.35)	0.62 (0.53+0.09)
SHRRC	0.60 (0.09+0.51)	0.59 (0.44+0.15)	0.31 (0.25+0.06)
Const. 1857	0.69 (0.53+0.16)	0.08 (0.02+0.06)	0.61 (0.54+0.07)	0.56 (0.44+0.13)
RBAGC	0.69 (0.06+0.63)	0.61 (0.29+0.32)	0.33 (0.02+0.31)	0.33(0.12+0.21)	0.60 (0.31+0.29)
Rodeo del Rey	0.58 (0.54+0.04)	0.72 (0.55+0.17)	0.58 (0.02+0.56)	0.64 (0.08+0.56)	0.72 (0.53+0.19)	0.72 (0.02+0.70)
B)
Laguna Hanson	0.75 (0.62+0.13)
HDRC	0.79 (0.74+0.05)	0.81 (0.78+0.03)
SHRRC	0.61 (0.58+0.03)	0.79 (0.70+0.09)	0.65 (0.59+0.06)
Const. 1857	0.72 (0.24+0.48)	0.42 (0.05+0.37)	0.76 (0.57+0.19)	0.72 (0.34+0.38)
RBAGC	0.69 (0.24+0.45)	0.78 (0.70+0.08)	0.54 (0.12+0.42)	0.64 (0.15+0.49)	0.59 (0.56+0.03)
C)
Laguna Hanson	0.87 (0.78+0.09)
HDRC	0.74 (0.67+0.07)	0.89 (0.86+0.03)
SHRRC	0.69 (0.44+0.24)	0.77 (0.75+0.02)	0.63 (0.52+0.11)
Const. 1857	0.85 (0.60+0.25)	0.34 (0+0.34)	0.84 (0.71+0.13)	0.63 (0.44+0.19)
RBAGC	0.76 (0.25+0.51)	0.83 (0.78+0.05)	0.64 (0.18+0.46)	0.62 (0.40+0.22)	0.70 (0.69+0.01)

Figure 2. 

Differences in species composition between Cucapá and the NPAs A birds B mammals C reptiles. Total difference in species composition (β_jac; complete bar), proportion of the difference due to species turnover (β_jtu; black portion of bar) and proportion of the difference due to nestedness (β_jne; gray portion of bar).

To our knowledge, this is the first study that integrates information on the diversity of terrestrial vertebrates that inhabit Cucapá and analyzes its conservation value. Our results indicate that Cucapá is home to a considerable number of bird, mammal, and reptile species. The number of species recorded in Cucapá represent 22% of the 473 bird species (Erickson et al. 2013), 48.5% of the 70 species of mammals (Guevara-Carrizales et al. 2016), and 14% of the 99 reptile species (Hollingsworth et al. 2015) reported from Baja California state. These percentages take on a greater importance considering that Cucapá occupies only 0.5% of the state.

The geographic distribution of bird, mammal, and reptile records available through GBIF, iNaturalist, and eBird indicates that large areas of Cucapá remain unexplored. Furthermore, some nearby NPAs (e.g. Parque Nacional Constitución de 1857 and Laguna Hanson) hold greater richness in considerably smaller areas. Thus, we consider that species richness of terrestrial vertebrates in Cucapá might actually be higher than what we report here, especially considering that at least 41, five, and 14 additional species of birds, mammals, and reptiles respectively have been recorded in nearby locations (Hathaway 2000; Guevara-Carrizales et al. 2013) and could inhabit Cucapá. Further efforts in unexplored areas of Cucapá are needed to complement the biological inventory of terrestrial vertebrates presented here. Population-level studies in the region, especially of threatened and endangered species, would be desirable to deepen our understanding of the conservation value of this region. Considering that the lowest elevation of Cucapá is essentially at sea level, future studies could consider climate change predictions in order to evaluate the persistence of species under future scenarios (e.g. with reptiles, see Lara-Reséndiz et al. 2020; Pérez-Delgadillo et al. 2021).

The inclusion of records from three different data sources provided complementary contributions to the inventory of Cucapá. The high percentage of bird, mammal, and reptile species recorded during fieldwork (78%, 79%, and 71%, respectively) and the percentage of species recorded exclusively by this method (20% for birds, 35% for mammals, and 35.7% for reptiles) indicate the importance of field sampling efforts to the species inventory for this relatively unexplored area. It also suggests the need for further fieldwork in areas that still lack information, but seasonal variations in species composition and overall activity should be considered. In the case of birds, for instance, seasonal changes are particularly marked due to migratory processes (Danemann et al. 2002). The contribution of records from citizen science platforms was notable for birds, with 76% of all species that we recorded being reported there, and 18% of species recorded exclusively with this data source. This demonstrates the utility of such platforms for studies that integrate knowledge of species diversity and that evaluate the conservation value of areas that are poorly explored and of which little is known of their flora and fauna (Schmiedel et al. 2016). The effectiveness and precision of birdwatchers, for example on the eBird platform, have been linked to the experience and high level of interest in the group, since the identification skills of the participants have been inferred to be as good as those of ornithologists with scientific training (Lukyanenko et al. 2016).

The number of species listed in the NOM-059 (Table 1) highlights the value of Cucapá as an important area in the region for the conservation of terrestrial vertebrates. In the case of birds, it is particularly important for the presence of raptor species threatened with extinction (genera Accipiter, Buteo, Parabuteo, and Athene), and of species considered threatened throughout North America such as Athene cunicularia and Lanius ludovicianus (CCA 2000; SEMARNAT 2010), since several of these migrant species require natural areas along their migration route. For mammals, it is worth highlighting the presence in Cucapá of threatened species that need large areas of land due to their environmental requirements, such as Ovis canadensis (SEMARNAT 2010), which is considered a flagship species in the arid-mountainous ecosystems of Mexico (SPABC 2012) and whose Peninsular subspecies (Ovis canadensis nelsoni) is considered Endangered in the USA according to the U.S. Fish and Wildlife Service (https://ecos.fws.gov/ecp/species/4970). Cucapá is thus important for the conservation of this species in situ because of the extension of habitat it conserves and because it connects parts of the Sistema de Humedales Remanentes del Río Colorado located to the west and east of Cucapá (Fig. 1). In the case of reptiles, besides the presence of four Threatened and three Subject to Special Protection species, there is one particular species not listed neither in the IUCN or NOM-059 which we consider makes Cucapá a priority area for conservation. This is Crotaphytus grismeri, a lizard endemic to Cucapá and Sierra El Mayor (McGuire 1994), which is another unprotected mountainous area south of Cucapá. Therefore, C. grismeri is not included in any NPA (Ramírez-Acosta et al. 2012). This illustrates that there is no need to wait until a species with particular ecological requirements is considered to be under a risk category to start protecting it.

The diversity of vertebrates and the number of species under risk categories reported in this study suggest that Cucapá represents an important conservation region and an opportunity for biological conservation in the northern Peninsula. Currently, Cucapá is not under any legal protection scheme and is therefore not within the NPAs system, not even within the priority terrestrial regions of the state of Baja California (Arriaga et al. 2000a, 2000b) or any other initiative that would provide for its protection in the future. Both in the interior and in the surroundings of the Sierra, various anthropogenic activities threaten its biodiversity (e.g. mining, agriculture, off-road racing, and illegal looting of species for sale; Mellink 1995). Additionally, the recently approved Proyecto Integral EcoZoneMX will allow activities that include mining, commercial construction, and a photovoltaic farm in an area of 14,782 ha (VRM 2015) that overlaps with more than 40% of Cucapá, which would have considerable negative effects on its biodiversity.

We found that Cucapá harbors high bird, mammal, and reptile species richness. Considering the number and size of unexplored areas, as well as the cryptic behavior and generally low detection probabilities of some species or groups (e.g. reptiles), species richness could be even higher than what we report here. The Cucapá Sierra has a particular species composition of the three groups of vertebrates, with high species turnover with three or more NPAs, and it harbors several species in risk extinction categories as well as endemic species. Taken together, these characteristics indicate that Cucapá has a complementary conservation value to the NPAs system of a region that has been severely transformed by various human activities. The lack of records in certain areas indicates the need to carry out further fieldwork to complement the species inventory reported here. In terms of conservation, we recommend the urgent establishment of strategies for the protection of Cucapá and its biodiversity.

We thank the technical staff of Unidad de Servicios Altamente Especializados del Instituto de Ecología, A.C. for help with fieldwork. Thanks are extended to Paulina García for producing the map. Milton Díaz Toribio, Rosaura Valdez and Sergio Cabrera provided helpful suggestions that improved this manuscript. Margaret Schroeder revised the English of the manuscript. The authors have no funding, and no conflicts of interest to report.