The Mexican scrub-jay (Aphelocoma wollweberi) is a species of scrub-jay found in Mexico and parts of the southwestern United States. Its range extends from southern California and Arizona in the United States south through Baja California and mainland Mexico to southern Oaxaca.
Quick Facts
Here are some key facts about the range of the Mexican scrub-jay:
- Native to Mexico and the southwestern United States
- Range extends from southern California and Arizona south to Oaxaca, Mexico
- Partially migratory – northern populations migrate south for the winter
- Found in arid scrublands, deserts, and pine-oak forests
- Closely related to the Florida scrub-jay and the island scrub-jay
Geographic Range
The Mexican scrub-jay has an extensive range spanning parts of two countries. Their range extends from southern California and Arizona in the United States south through the Baja California peninsula and mainland Mexico. It reaches as far south as Oaxaca.
In the United States, Mexican scrub-jays are found in southern California, including areas like San Diego and the Transverse Ranges, and just into southern Arizona. They are generally limited to areas west of the deserts in both states.
The jays occupy both the Pacific and Gulf coastal slopes in Mexico. On the Pacific side, they are found from central Sonora south to Oaxaca. On the Gulf side, their range stretches from Tamaulipas south to northern Oaxaca.
Mexican scrub-jays occupy several major habitat types across their large range. These include:
- Arid scrublands
- Deserts
- Oak and pine-oak forests
- Edge habitats between forests and scrublands
They are found across a range of elevations from sea level up to around 2,600 m in oak-pine forests in the interior highlands of Mexico.
Clinal Variation
Mexican scrub-jays show subtle clinal variation in size and color across their range. Clinal variation refers to gradual changes in characteristics across the geographical range of a species. Jays in the northernmost part of the range tend to be slightly larger and paler blue than birds in the southern areas.
For example, birds in California and Arizona (United States) tend to average a little larger than birds in southern Mexico. Similarly, jays in the northern areas have paler blue upperparts compared to the darker blue-toned birds in Oaxaca and areas farther south.
These minor differences in size and color likely reflect adaptation to local environmental conditions. The more subtle variations don’t warrant dividing the jays into different subspecies.
Partially Migratory
The Mexican scrub-jay is partially migratory over its range. Populations in the northernmost areas of California, Arizona, New Mexico, and Mexico migrate southward in winter months. Birds in southern Arizona may wander locally in winter but do not typically leave the state.
Farther south, the jays are non-migratory. For example, populations in central Sinaloa, the Baja California peninsula, and south do not migrate. The differences in migratory tendency are linked to the harsher winters in the northern parts of the range.
Closely Related to Other Scrub-Jays
The Mexican scrub-jay is closely related to two other species of scrub-jay found in restricted ranges of the United States:
- Florida scrub-jay – Found only in Florida
- Island scrub-jay – Native only to Santa Cruz Island off the coast of southern California
These three jays were previously considered a single species – the western scrub-jay. Based on differences in morphology, behavior, genetics, and range, the Mexican and Florida populations are now classified as distinct species.
All three scrub-jay species have similar habits adapted for living in arid scrublands. However, the Mexican scrub-jay has a much larger range extending thousands of miles into Mexico.
Declines and Threats
Overall populations of the Mexican scrub-jay appear to be declining in many areas, especially in the northernmost parts of its range. However, the species remains relatively common over much of Mexico.
Some key threats to the jays include:
- Habitat loss and degradation
- Urbanization and agricultural development
- Climate change – may threaten marginal populations
- Nest parasitism by brown-headed cowbirds
Ongoing habitat destruction across the Baja California peninsula and southern Arizona is especially concerning for the jays. Preserving patches of oak woodland and other key habitats will be important for the long-term outlook of the species.
Conclusion
In summary, the Mexican scrub-jay occupies an extensive range spanning the southwestern US and Mexico. Its range reaches from southern California and Arizona south to Oaxaca. The birds inhabit desert scrublands, arid woodlands, pine-oak forests, and other habitats. Northern populations are migratory while southern groups are year-round residents. Ongoing habitat loss poses the biggest threat to the species’ long-term survival.
