Avian Diversity on a University Campus in the Mexican Chihuahuan Desert

Abstract

Urban green spaces in arid environments can serve as biodiversity reservoirs, yet their ecological contributions remain underexplored. This study assessed avian diversity on the Universidad Autónoma Chapingo campus Unidad Regional Universitaria de Zonas Áridas (URUZA) in the Chihuahuan Desert, northern Mexico. From February 2022 to April 2025, bird surveys were collected through point transects and photographic records. The species were categorized by seasonality status, trophic guild, and conservation status according to the IUCN Red List and Mexican NOM-059. The Shannon, Margalef, Jaccard, and Bray–Curtis Indices were used to analyze diversity. Statistical analysis was undertaken with log-linear models to evaluate spatial and functional patterns. A total of 90 bird species, including protected and vulnerable species, were identified, belonging to 16 orders and 35 families. The areas with the greatest diversity of vegetation and water bodies also presented the greatest diversity and richness of bird species. Resident birds dominated species richness and trophic structure, although migratory birds contributed to functional heterogeneity. Significant differences were observed between seasonality and trophic guilds. This study demonstrates that the campus contributes to sustainability by preserving biodiversity in arid land, educating the community about the importance of conservation, and laying the groundwork for more informed and sustainable environmental and economic management.

1. Introduction

Although worldwide population growth has slowed, biodiversity loss is predicted to increase over the next 20 years as compared to the previous 20 years, particularly in historically sensitive regions [1]. This loss is related to the most important components of the effect of population growth, such as the loss of vegetation due to increased population density and the human footprint [2]. Ecologists have recently begun to focus on pockets of urban green spaces [3] as potential conservation zones. In particular, these green areas are ecologically important for sustaining bird diversity in urban environments, including areas with native and introduced vegetation within metropolitan boundaries. Green spaces include public and recreational parks, sports facilities, artificial wetlands, and protected natural areas such as national parks, ecological reserves, and university campuses [4].

Since the 1940s, at least 300 universities have conducted biodiversity studies on their campuses, including bird diversity, highlighting these areas as urban green important spaces for biodiversity research and education [5]. Particularly in metropolitan areas, where habitat fragmentation and loss endanger birds, these university campuses serve as biodiversity reservoirs. Several international studies have shown that campuses can host a surprising richness of bird species [6,7,8]—including those that are threatened—thanks to the presence of green areas, water bodies, diverse food resources and habitats, and lower levels of human disturbance compared to the surrounding urban environment [9,10,11].

Moreover, arid and semi-arid lands support a wide variety of bird habitats. Specifically, deserts and other arid regions of North America provide homes for a huge variety of migratory winter species from southern Canada and the central United States [12], in addition to the species that reside in the region. The arid zones of Mexico are home to a significant diversity of these bird species. The Chihuahuan Desert, located in northern Mexico and the southwestern United States, is known as the most important wintering area for 85% of the grassland birds that breed in the Great Plains [13], as well as several threatened or endangered species in Mexico. Unfortunately, this region has experienced significant biodiversity loss over the past 30 years [14], primarily due to human activities and climate change. Although it is well documented that university campuses are important areas for biodiversity conservation [5], few biodiversity studies have been conducted on university campuses in the Chihuahuan Desert region, and none specifically on bird biodiversity.

Our study sought to fill this gap by assessing avian diversity on the Unidad Regional Universitaria de Zonas Áridas (URUZA), a university campus located in the Chihuahuan Desert region in northern Mexico. The objective was to determine whether this space—considering the plurality of its natural resources—serves as a reservoir of diversity for resident and migratory birds, by recording species, assessing their conservation status, and analyzing the relationship between sampling sites, seasonal status, and trophic guilds.

2. Materials and Methods

2.1. Study Area

The Unidad Regional Universitaria de Zonas Áridas (URUZA) of the Universidad Autónoma Chapingo (UACh) is located at the coordinates 25°53′43.783″ N, 103°36′7.82″ W, near the small town of Bermejillo in Durango state, Mexico (Figure 1). This region is part of the geographic subprovince “Bolsón de Mapimí” located in the Chihuahuan Desert, which has a very arid, semi-warm climate according to the Köppen classification adapted for Mexico [15], with little rainfall, an annual average of 264 mm, and extreme temperatures ranging from an average minimum of 3.9 °C to an average maximum of 37.41 °C [16]. The vegetation corresponds to xerophilous scrubland and is characterized by microphyll scrubland and chaparral of various compositions with halophytic flora [16,17], making it a typical ecosystem of the arid zones of Mexico.

This university campus has a variety of land uses, including the following: residential use (classrooms, laboratories, and sports areas); experimental agricultural farms (sunflowers, fruits, cacti, etc.) and production farms (forage maize, alfalfa, sorghum, etc.); livestock areas (cattle, sheep, and poultry); two artificial bodies of water; and natural areas with pastures, scrublands, and trees. The entire area is approximately 260 hectares. The campus vegetation consists of introduced and endemic species, including Phoenix dactylifera, Vachellia farnesiana, Neltuma spp., Larrea tridentata, Opuntia spp., Yucca thompsoniana, Atriplex canescens, Ehretia tinifolia, Parkinsonia spp., Nerium oleander, and Salsola spp.

2.2. Field Methods

The university campus was divided into four sample zones according to the type of use assigned (agricultural, livestock, buildings, etc.), as seen on the above map (Figure 1). Site 1 represents a location with significant human impact, including administrative, academic, and recreational buildings. Site 2 is an experimental agricultural zone in which sunflowers, cacti, pumpkin, melon, marigold, and other products are cultivated. Site 3 relates to agricultural areas for animal production, in which mainly maize, sorghum, and alfalfa are cultivated. In addition, it comprises an agricultural production unit that raises rabbits, goats, lambs, chickens, beef cattle, and ostriches. The site also includes an irrigation reservoir in which tilapia fish are occasionally raised. Finally, site 4 has a big fodder crop area, similar to site 3. This location also features an irrigation reservoir and a farm with 600 dairy cows.

A bird census was conducted from February 2022 to April 2025, using the point transect method because of its efficiency in estimating species diversity in changing environments [18]. This method involves walking along the transect and stopping at predefined spots, allowing time for the birds to settle (one minute), and then recording all birds observed during a 15 min period. A distance of at least 150 m was left between each observation point. Two morning and two afternoon surveys were carried out in each season, within the first three hours after sunrise and within the last three hours before sunset, on days with clear weather without rain or strong winds, and with approximately three weeks between each survey. All the bird species at each observation location were documented via photographic recording, using digital cameras (Nikon P950 and Nikon P1000) for subsequent identification. This study only considered the presence or absence of species at each observation location, not the number of individuals per species. We complemented our records by consulting the online citizen science resources, iNaturalistMX (available at https://mexico.inaturalist.org/, accessed on 16 April 2025) and eBird (available at https://ebird.org/home, accessed on 16 April 2025), considering only those with a research status that included photos of the perched bird.

For bird identification we used the Dunn and Alderfer [19] and the Sibley [20] field guides, which are standard guides for identifying North American birds, and Madero [21] a field guide for birds of northern Mexico. The taxonomy and nomenclature used followed the proposal of the American Ornithological Society [22]. The conservation status of the species was classified using the worldwide Red List of Threatened Species (IUCN) [23], as well as the Mexican national legislation NOM-059-Semarnat-2010 (NOM-059) [24] list of endangered, threatened, and protected species. Each species was assigned one of the following seasonality categories: resident (R), which breeds in the region and can be observed year-round; and migratory (M), which is only found in the region during certain seasons of the year. The migratory species included winter migratory species (which breed in Canada and the northern United States, and which spend the winter in Mexico or further south), summer migrants (found in Mexico during the breeding season from March to September), and transient species (which use the area as a stopover during migration south in the fall or north in the spring). Seasonality was determined with information generated by the Mexican Bird Knowledge Network [25]. Based on González-Salazar et al. [26], the feeding guilds were divided into the following categories: omnivore (Om), carnivore (Ca), scavenger (Sc), insectivore (In), nectarivore (Ne), granivore (Gr), piscivore (Pi), and frugivore (Fr).

2.3. Diversity Analysis

We calculated the Shannon–Wiener Index ($H^{\prime }$) and the Margalef Richness Index to assess the species diversity on each site. The Jaccard Similarity Index and the Bray–Curtis Dissimilarity were computed to analyze the differences in site functional structure, with the former based on species presence or absence and the latter taking into account the abundance of each trophic guild. Diversity and similarity indices were calculated for all the species combined and for the migratory and resident species individually to assess species composition overlap. Finally, a Non-Metric Multidimensional Scaling (NMDS) analysis utilized the previously obtained Bray–Curtis Dissimilarity matrix. The diversity and similarity indices and the NMDS analysis were performed using PAST version 4.17. Graphical visualizations were created in Python version 3.11.5, using the matplotlib version 3.7.2 [27], seaborn version 0.12.2 [28], and plotly version 5.14.1 packages.

2.4. Statistical Analysis

A log-linear hierarchical model was used to determine the relationship between sample site, seasonality, and trophic guild. Data on trophic guild abundance by site and seasonality were grouped into a three-dimensional contingency table containing the variables ‘Site’, ‘Seasonality’, and ‘Trophic Guild’. A saturated log-linear model was developed, which included all possible interactions between the three variables. The goodness-of-fit of the saturated model was confirmed with a likelihood ratio statistic (X²). Subsequently, a hierarchical descent modeling strategy was adopted to identify the most parsimonious association structure. Likelihood ratio tests (LRs) were performed to compare nested models, evaluating the significance of the third-order interaction and the second-order interactions. A post hoc Chi-square test of independence was applied to examine the nature of the significant relationships, and standardized adjusted residuals were computed. To control the false discovery rate in multiple comparisons, we used a Benjamini–Hochberg (BH) correction to the p-values associated with these residuals. A significance level of $\alpha =0.05$ was established. All statistical analyses were performed using R software, version 4.0.0 [29]. The loglm() functions from the MASS package were used for log-linear modeling, and stdres() from the stats package was used for standardized adjusted residuals.

3. Results

In total, 90 bird species belonging to 16 orders and 35 families were identified (Figure 2a). The complete record is listed in

Table A1. Alphabetical checklist of bird species recorded from the Unidad Regional de Zonas Áridas located in Durango, Mexico. Seasonality: migratory (M) and resident (R). Conservation status: near threatened (NT), special protection (Pr), threatened (A). Trophic guilds: carnivore (Ca), scavenger (Sc), frugivore (Fr), granivore (Gr), insectivore (In), nectarivore (Ne), omnivore (Om), piscivore (Pi). NOM-059: Mexican national legislation list of endangered, threatened and protected species.

Specie	Comun Name	Seasonality	IUCN Red List	NOM-059	Feeding Guild
Agelaius phoeniceus	Red-winged Blackbird	R			In
Amphispiza bilineata	Black-throated Sparrow	R			Om
Anas diazi	Mexican Duck	R		A	Om
Anser caerulescens	Snow Goose	M			Om
Archilochus alexandri	Black-shinned Hummingbird	M			Ne
Archilochus colubris *	Ruby-throated Hummingbird	M			Ne
Ardea ibis	Western Cattle Egret	R			In, Pi
Athene cunicularia	Burrowing Owl	R			Ca
Auriparus flaviceps	Verdin	R			In, Fr
Bubo virginianus	Great Horned Owl	R			Ca
Buteo jamaicensis	Red-tailed Hawk	R			Ca
Buteo swainsoni	Swainson’s Hawk	M		Pr	Ca
Callipepla squamata	Scaled Quail	R			Gr
Campylorhynchus brunneicapillus	Cactus Wren	R			In
Cardellina pusilla	Wilson’s Warbler	M			In
Cardinalis sinuatus	Pyrrhuloxia	R			Gr
Cathartes aura	Turkey Vulture	R			Sc
Charadrius vociferus	Killdeer	R	NT		In
Chondestes grammacus	Lark Sparrow	R			Gr
Chordeiles acutipennis	Lesser Nighthawk	R			In
Colaptes auratus	Northern Flicker	M			In
Columba livia	Rock Pigeon	R			Gr
Columbina inca	Inca Dove	R			Gr
Contopus cooperi	Olive-sided Flycatcher	M	NT		In
Contopus sordidulus	Western Wood-Pewee	M			In
Coragyps atratus	Black Vulture	R			Sc
Corthylio calendula	Ruby-crowned Kinglet	M			In
Corvus corax	Common Raven	R			Om
Dryobates scalaris	Ladder-backed Woodpecker	R			In
Elanus leucurus	White-tailed Kite	R			Ca
Empidonax hammondii	Hammond’s Flycatcher	M			In
Empidonax oberholseri	Dusky Flycatcher	M			In
Empidonax wrightii	Gray Flycatcher	M			In
Falco sparverius	American Kestrel	R			In, Ca
Fulica americana	American Coot	R			Om
Geococcyx californianus	Greater Roadrunner	R			Om
Geothlypis tolmiei	MacGillivray´s Warbler	M		A	In
Haemorhous mexicanus	House Finch	R			Gr
Himantopus mexicanus	Black- necked Stilt	M			In, Pi
Hirundo rustica	Barn Swallow	M			In
Icteria virens	Yellow-breasted Chat	M			In, Fr
Icterus cucullatus	Hooded Oriole	M			In
Lanius ludovicianus	Loggerhead Shrike	R	NT		In, Ca
Leiothlypis celata	Orange-crowned Warbler	M			In, Fr
Megaceryle alcyon	Belted Kingfisher	M			Pi
Megaceryle alcyon	Melanerpes aurifrons	R			In, Fr
Melospiza lincolnii	Lincoln’s Sparrow	M			Gr
Mimus polyglottos	Northern Mockingbird	R			Om
Molothrus aeneus	Bronzed Cowbird	R			In, Gr
Molothrus ater	Brown-headed Cowbird	R			In
Myiarchus cinerascens	Ash-throated Flycatcher	M			In
Numenius americanus	Long-billed Curlew	M			In, Ca
Nycticorax nycticorax	Black-crowned Night Heron	R			Pi, In, Ca
Parabuteo unicinctus	Harris’s Hawk	R		Pr	Ca
Passer domesticus	House Sparrow	R			Gr
Passerculus sandwichensis	Savannah Sparrow	M			Gr, In
Passerina caerulea	Blue Grosbeak	M			Gr
Passerina ciris	Painted Bunting	M		Pr	Gr
Passerina cyanea	Indigo Bunting	M			In, Gr
Petrochelidon fulva	Cave Swallow	M			In
Pipilo chlorurus	Green-tailed Towhee	M			Gr, In
Piranga ludoviciana	Western Tanager	M			In, Fr
Polioptila caerulea	Blue–gray Gnatcatcher	M			In
Polioptila melanura	Black-tailed Gnatcatcher	R			In
Pooecetes gramineus	Vesper Sparrow	M			Gr, In
Pyrocephalus rubinus	Vermilion Flycatcher	R			In
Quiscalus mexicanus	Great-tailed Grackle	R			Om
Sayornis phoebe	Eastern Phoebe	M			In
Sayornis saya	Say’s Phoebe	R			In
Setophaga coronata	Yellow-rumped Warbler	M			In, Fr
Setophaga townsendi	Townsend’s Warbler	M			In
Spatula discors	Blue-winged Teal	M			Om
Sphyrapicus nuchalis	Red-naped Sapsucker	M			In, Fr
Sphyrapicus varius	Yellow-bellied Sapsucker	M			In, Fr
Spinus psaltria	Lesser Golgfinch	R			Gr
Spizella breweri	Brewer’s Sparrow	M			In, Gr
Spizella pallida	Clay-colored Sparrow	M			Gr
Spizella passerina	Chipping Sparrow	M			Gr
Streptopelia decaocto	Turkish collar Dove	R			Gr
Toxostoma curvirostre	Curve-billed Thrasher	R			In
Troglodytes aedon	Northern House Wren	M			In
Turdus migratorius	American Robin	M			In
Tyrannus verticalis	Western Kingbird	M			In
Tyrannus vociferans	Cassin’s Kingbird	M			In
Tyto furcata	Barn Owl	R			Ca
Vireo cassinii *	Cassin’s Vireo	M			In
Xanthocephalus xanthocephalus	Yellow-headed Blackbird	M			Gr
Zenaida asiatica	White Dove	R			Gr
Zenaida macroura	Mourning Dove	R			Gr
Zonotrichia leucophrys	White-crowned Sparrow	M			Gr, In

^* Record taken from iNaturalistMX.

. Regarding families, Tyrannidae had the highest number of species with 11, followed by Passerellidae with 10, Icteridae with 7, and Cardinalidae, Columbidae, Picidae, and Parulidae with 5 each (Figure 2b). These seven families represented 53.33% of the total number of recorded species. In terms of seasonality, 47 (52%) species were migratory and 43 (47%) were residents. Site 1 stands out as the habitat with the highest species abundance, with almost equal contributions from both the migratory and the resident species. Sites 2, 3, and 4 had a similar amount of species, as seen in Figure 2c.

Regarding the IUCN list, three species were in the near threatened (NT) category (Figure A1): (Contopus cooperi), Killdeer (Charadrius vociferus), and Loggerhead Shrike (Lanius ludovicianus). According to NOM-059, three species were subject to special protection (Pr): Harris’s Hawk (Parabuteo unicinctus), Painted Bunting (Passerina ciris), and Swainson’s Hawk (Buteo swainsoni); and there were two threatened species (A): MacGillivray’s Warbler (Geothlypis tolmiei) and Mexican Duck (Anas diazi). We found four semi-endemic species (Figure A2), i.e., they are only found in Mexico at specific times of year: Cassin’s Kingbird (Tyrannus vociferans), Cassin’s Vireo (Vireo cassinii), Clay-colored Sparrow (Spizella pallida), and Gray Flycatcher (Empidonax wrightii).

Bird diversity, assessed using the Shannon and Margalef Indices, showed variations among the four sampling sites (

Table 1. Diversity indices divided by sampling site and seasonal status.

	Shannon			Margalef
Sites	Total	Resident	Migratory	Total	Resident	Migratory
Site 1	4.74	3.98	4.10	16.24	9.15	9.97
Site 2	4.27	3.81	3.24	11.36	8.10	5.41
Site 3	4.10	3.74	2.85	9.97	7.65	4.17
Site 4	4.27	3.85	3.18	11.36	8.32	5.17

). According to the Shannon Index, site 1 showed the highest total diversity value (4.74), while site 3 had the lowest (4.10), indicating high diversity on all the sites. When comparing the resident and migratory species, it was observed that the diversity of the resident species was slightly higher on all sites, except for site 1. This pattern suggests a lower contribution of the migratory species to the overall community structure on most of the sites studied. The Margalef Index, which measures species richness, reported total values ranging from 9.97 to 16.24. Site 1 had the highest total richness, suggesting a higher number of species than the other sites. Except for site 1, the richness of the resident species was also greater than that of the migratory species. The observed distribution suggests a community structure predominantly driven by the resident species, with the migratory species making a comparatively smaller contribution to the ecosystem’s overall richness. However, all the values obtained indicated high richness on all the sites.

Figure 3 presents the results of the Jaccard Index segmented by resident and migratory birds. When only resident birds were included (Figure 3a), the similarity values ranged from 0.43 to 0.65. Sites 1 and 2 had the most similarity (0.65), followed by sites 2 and 3 (0.64). In contrast, the similarity across the sites that solely included migratory species (Figure 3b) declined significantly, with values ranging from 0.12 (sites 2 and 3) to 0.62 (sites 3 and 4).

Regarding trophic guilds, insectivores and granivores were the most prevalent on all the sites, both resident and migratory, as seen in Figure 4. The resident bird community contributed most abundantly to all the trophic groups, except insectivores on sites 1 and 2, as seen in Figure 4a). Nectarivorous birds were exclusively migratory (Figure 4b), while scavengers were resident and only present on site 4, probably because it was the most remote and extensive site, with less human disturbance and a greater likelihood of finding dead animals.

Considering the trophic structure of the birds on the four sampling sites, Bray–Curtis Dissimilarity was applied to complement the similarity analysis in species composition. When only resident birds were included (Figure 5a), the Bray–Curtis matrix indicated high dissimilarities between sites, with values ranging from 0.81 to 0.97. The dendrogram shows that sites 2 and 3 formed a cluster (overlapping almost completely), while site 4 was segregated. According to the NMDS graph (Figure 5c), site 1 was connected with frugivores and insectivores. Sites 2 and 3 were related to insectivores, granivores, carnivores, and omnivores. Site 4 was linked to piscivores and scavengers.

The trophic structure of the migratory birds displayed the greatest dissimilarities (up to 0.82, Figure 5b). The dendrogram clearly distinguishes site 1 from the others, although sites 3 and 4 are clustered together. The NMDS graph (Figure 5d) shows that site 2 was clearly separated from the others, while sites 3 and 4 were quite near and were connected to granivores, carnivores, and omnivores. Site 1 had a greater relationship to frugivores and nectarivores, but it was also related to insectivores and granivores.

Finally, we used a log-linear hierarchical model test to investigate the patterns of connection between feeding guilds, seasonal status, and sample site. The significance of the third-order interaction (Site–Seasonality–Guild) was tested by comparing the saturated model with one that included all second-order interactions (Site–Seasonality + Site–Guild + Seasonality–Guild). The test of this third-order interaction was not significant. This indicates that a model with only second-order interactions is sufficient to represent the data structure. When assessing the significance of each second-order interaction individually, the comparisons were as follows: Site–Seasonality was not significant; Site–Guild was not significant; Seasonality–Guild was statistically significant ($X^2=25.27911,df=7,p=0.00068$). To determine which combinations of seasonality and trophic guild contributed most to significance, a post hoc analysis with Benjamini–Hochberg correction was performed. No combination was statistically significant. This means that the pattern of trophic guilds differs between resident and migratory birds; however, this difference is not due to the abundance of a particular guild for a specific seasonal status.

4. Discussion

4.1. Richness and Abundance

Over the three-year observation period, 90 bird species were recorded, of which 89 were by fieldwork. Only one record was taken from iNaturalistMX, while eBird did not have any reports of birds within the university campus. Studies conducted in nearby areas such as the Mapimí Biosphere Reserve, a protected natural area located in the central part of the Chihuahuan Desert, have documented 149 bird species [30]. On the other hand, a recently published study for the microphyll desert scrubland of southeastern Mapimí [31], which borders the campus, identified 112 bird species. Finally, the total birdlife recorded in Durango state is 516 species [32]. Our study covered 60.4% of the birds reported in the first study, 80.35% of the species documented in the second, and 17.44% of the total species in the state. Although the university campus has a smaller surface than the aforementioned study areas (0.075%, 0.71%, and 0.002%, respectively), it has the potential to support a large number of bird species.

The diversity and uniformity of the distribution of sampling sites in this study, calculated using the Shannon Index, yielded values corresponding to high diversity for both migratory and resident species [33], except for the migratory species on site 3, where diversity was classified as medium. The richness evaluated using the Margalef Index indicated that for both resident and migratory birds all the sites had values above 4.0, which corresponds to high richness [33]. Compared to other university campuses in arid areas [34], URUZA achieved higher diversity rates. These findings highlight the importance of the university campus, which is regarded as a more functional ecosystem due to the diversity of food sources available [35]. The results of the Jaccard Index suggests that resident bird communities are more homogeneous across locations. This might be attributed to resilient adaptation to the local environment and human activity, or to greater temporal permanency, enabling them to thrive in any microhabitat on campus [36,37]. In contrast, migratory birds do not use all sites uniformly, as there is low similarity between sites. They likely choose certain habitats based on their temporal needs, such as resting, eating, or shelter during migration [38].

Figure 6 shows that birds prefer specific areas within the university campus. We observed that orchards attracted the largest number of birds (the zone in red), finding more than 15 species within a 50m radius, most of which were migratory birds. This tendency is consistent with the findings of Nolfork et al. (2014) [39], who found that orchards in arid lands attract a wider range of birds. Artificial water bodies are also a more species-rich environment (the zones in blue and green). This is also consistent with the literature, which reports that water sources (both artificial and natural) contribute to the greater abundance and richness of birds in arid lands [40,41]. These water points are of utmost importance: they contribute to the richness and abundance of bird species, and permanent access to water lessens the danger of mortality from dehydration, mainly for small birds such as passerines [42,43].

4.2. Seasonality and Trophic Guilds

Granivores and insectivores were the trophic guilds with the greatest presence on all the sites. This may be linked to the greater abundance of insects present in farmland and orchards, as fertilizers and pesticides are not used on all of them [44], due to various experimental studies carried out throughout the year. In addition, these crops and orchards provide diverse food sources for granivorous birds.

When we studied the resident birds separately, all the sites were slightly dissimilar from one another, according to the Bray–Curtis Index, with site 4 being the most dissimilar and linked to piscivores and scavengers, according to the NMDS graph, although it also showed a high presence of carnivores. This trophic guild may be connected with the presence of small mammals [45] and reptiles drawn to the cattle feed available on the site. On the other hand, this site contains an artificial body of water with surrounding vegetation but no fish, suggesting that piscivores utilize it as a resting spot.

In contrast, the migratory birds exhibited a significant degree of dissimilarity. Site 1 was the most dissimilar and closely connected to frugivores, nectarivores, insectivores, and granivores. This location features the most diversified vegetation, including tree species such as Tamarix aphylla, along with cacti, shrubs, weeds, two organic gardens, and water sources. These resources provide abundant food, shelter, and nesting opportunities, making the site particularly attractive to migratory birds. In summary, resident birds mainly shape the central trophic structure, while migratory species introduce specialized and seasonal niches, enhancing trophic variability between the sites.

4.3. The Campus as a Refuge for Protected Birds

Among North American songbirds, insectivores and long-distance migrants have experienced some of the sharpest population declines in recent years [46,47]. This study recorded the Olive-sided Flycatcher (Contopus cooperi) (Figure A1H), an insectivorous migratory species that travels from South America to North America to breed during the summer, and whose population has declined dramatically [48]. This bird was observed feeding and perching on a Tamarix aphylla tree on site 2, where insects are abundant thanks to the flood irrigation of the crops there. The observation in April coincided with the period of its migratory return from South America to Alaska. Another grassland bird that has lost habitat due to intensive anthropogenic uses is the Loggerhead Shrike (Lanius ludovicianus) (Figure A1A). The decline of its population, mainly in the United States, led to its designation as NT on the IUCN list [49,50]. Although it is not a threatened species in Mexico and was frequently observed on campus during sampling, its conservation remains important. Another NT species found on campus is the Killdeer (Charadrius vociferus) (Figure A1C). This bird has adapted to human-modified environments, but this has made it vulnerable to human activity [51,52]. This bird was frequently observed in crop fields throughout the year, suggesting that it may nest on campus.

In terms of birds subject to special protection in Mexico, we found the Swainson’s Hawk (Buteo swainsoni) (Figure A1B), a migratory species that breeds in North America and usually spends the winter from Mexico to Argentina [53]. Although its population has been increasing over the last two decades [54], its monitoring and protection have not been neglected. On this campus, we observed both juvenile and adult individuals. Another protected bird of prey is the Harris’s Hawk (Parabuteo unicinctus) (Figure A1F), a resident species known for being a pest controller. Like the previous one, its population has been increasing [55] but it remains under protection in Mexico. Also protected is the Painted Bunting (Passerina ciris) (Figure A1G), a migratory species that winters from northwestern Mexico to Central America [56]. The illegal capture and trade of this species in Mexico is causing a decline in local populations [57]. In terms of endangered species, we found MacGillivray’s Warbler (Geothlypis tolmiei) (Figure A1D), a long-distance migratory bird that travels from Canada to northeastern Mexico. Although it is considered abundant globally, it is listed as endangered in the Greater Yellowstone Ecosystem and is a threatened species in Mexico [58]. The last endangered species found was the Mexican Duck (Anas diazi) (Figure A1E), a species that was not recognized as such until 2020 [59]. This meant that it was not added to the list of globally endangered species, but in Mexico it remains in that category.

Four semi-endemic species were recorded on campus. This category is designated by Mexico’s National Commission for the Knowledge and Use of Biodiversity (CONABIO) for species that are found only in the country during part of the year. The first of these species was the Cassin’s Kingbird (Tyrannus vociferans) (Figure A2M), a short-distance migratory bird that breeds in the southern United States and northern Mexico and moves south in the fall [60]. The next species was the Clay-colored Sparrow (Spizella pallida) (Figure A2N), a grassland bird that breeds in the Great Plains and spends the winter in Mexico. Although it is not a threatened species worldwide or locally, a population drop has been seen in recent decades [61]. The Gray Flycatcher (Empidonax wrightii) (Figure A2K), which is common throughout the winter in the semi-arid scrublands of northern Mexico, was also observed. Its population appears to be increasing [62]. The last species was the Cassin’s Vireo (Vireo cassinii) (Figure A2L), a migratory songbird that breeds in the forests of western North America. This record was taken from iNaturalistMX [63].

Finally, we identified numerous grassland birds that, while not considered endangered, have had population declines in recent years as a result of habitat loss and degradation in their breeding and wintering regions [64], including the Chihuahuan Desert. These included the White-crowned Sparrow (Zonotrichia leucophrys) (Figure A2G), the Lark Sparrow (Chondestes grammacus) (Figure A2H), the Brewer’s Sparrow (Spizella breweri), Lincoln’s Sparrow (Melospiza lincolnii) (Figure A2I), the Burrowing Owl (Athene cunicularia) (Figure A2J), the Savannah Sparrow (Passerculus sandwichensis), and the Vesper Sparrow (Pooecetes gramineus).

5. Conclusions

The structure of the university campus, including agricultural fields, organic gardens, man-made structures, and patches of native vegetation, contributes to increasing bird diversity [65,66], principally migratory. Artificial bodies of water help to increase the presence of birds while also protecting them from dehydration, particularly in smaller birds. This campus has the characteristics of being considered a bird reservoir; however, it is necessary to promote scientific research, continuous monitoring, and environmental education, fostering knowledge and awareness of the importance of conserving regional and global birdlife. The scientific dissemination of the campus biodiversity is equally vital for creating awareness among the university community and the public population, thereby strengthening the sense of institutional ownership, as well as managing resources to carry out new research related to this topic.

Finally, given that this study is a pioneering work in compiling a list of bird species present on a university campus in the arid land of the Mexican Chihuahuan Desert, the data collected and the results obtained could serve as a model for other university campuses or urban parks in arid areas, demonstrating that even in hostile environments, green infrastructure can be designed to maximize the benefit to biodiversity.