The phainopepla is a slender, crested, black bird found in the desert regions of the southwestern United States and northern Mexico. Its scientific name is Phainopepla nitens, with “phainopepla” meaning “shining robe” in Greek and referring to the adult male’s glossy black plumage. Phainopeplas are unique among North American passerines in that they subsist primarily on the berries of mistletoe, a parasitic plant. This unusual diet leads phainopeplas to have a complex migratory pattern as they track the fruiting cycles of different mistletoe species across the landscape. In this article, we will examine the migratory behavior of phainopeplas and attempt to answer the question: do phainopeplas migrate?
Phainopepla Natural History
Phainopeplas nest in trees and shrubs throughout the hot, arid deserts of the Southwest. Their breeding range extends from southern California, southern Nevada, southern Utah, and Colorado south through Arizona, New Mexico, and western Texas to Baja California, Sonora, and Chihuahua, Mexico. They are non-territorial birds, nesting in loose colonies where mistletoe is abundant. The male builds the nest and incubates the eggs while the female broods and feeds the young. Phainopeplas produce one brood per year, with the nesting season lasting from March through June across most of their range.
Phainopeplas take advantage of the asynchronous fruiting cycles of different mistletoe species to maintain access to berries year-round. In spring and summer, they feed on the fruits of mesquite mistletoe (Phoradendron californicum), which ripens from March to June. In fall and winter, they switch to eating viscidium berries of juniper mistletoe (Phoradendron juniperinum), which peak from October to December. They also opportunistically eat a wide variety of other fruits and insects to supplement their diet. The ability to utilize these seasonal food resources likely enables phainopeplas to remain resident across much of their range.
Evidence of Migration
While phainopeplas can be found year-round through most of their range, seasonal movements and migration do occur for some populations. The most well-studied migratory populations occur in Arizona and New Mexico. Here, phainopeplas breeding in mountain ranges at higher elevations move downslope for the winter, while lower elevation populations appear to remain resident.
Banding studies have documented migratory movements of upwards of 150 km from breeding sites in mountain ranges such as the Chiricahua, Pinaleño, Santa Catalina, and White Mountains to wintering areas in the Sonoran and Chihuahuan Deserts. The migrating birds begin leaving the mountains in September and October to winter in lower elevations areas such as the Gila River valley from October to March. In spring, they return to the mountains to breed once again.
Researchers have proposed several factors that may influence the migratory movements in these populations:
– Temperature – Moving to lower, warmer elevations in winter allows the birds to reduce thermoregulatory demands.
– Food availability – Lower elevations may provide more reliable food sources in winter.
– Water availability – Lower elevations have more open water.
– Intermittent breeding – Some populations may periodically skip breeding and migrate instead.
So in areas like southeastern Arizona, migratory movements following a vertical elevation gradient are well-documented in some phainopepla populations. But do phainopeplas always migrate seasonally?
Evidence for Residency
While migratory behavior occurs in some areas, evidence suggests phainopeplas are resident across significant portions of their range. In California, phainopeplas are considered resident, with no regular seasonal movements. Here, the availability of mistletoe fruits allows the birds to find food supplies year-round, negating the need for seasonal migration.
In desert regions like the Sonoran Desert of Arizona and Sonora, Mexico, phainopeplas seem to maintain permanent residency. Although local movements occur, there are no indications of regular seasonal migration out of these core desert areas. In the Mojave Desert of Nevada, California, and Utah, phainopeplas again appear to be year-round residents.
Across west Texas, phainopeplas are also thought to be non-migratory permanent residents, even though the region sees both hot summers and occasional cold winters. The key to their residency seems to be the presence of juniper mistletoe, which provides a dependable winter food source. Migrating to follow available food doesn’t seem necessary across much of the species’ range.
Researchers have radio-tracked phainopeplas in Arizona and found they maintain stable home ranges of around 100 hectares (250 acres) year-round. This also indicates they are not migrating seasonally across the landscape. So while migrations do occur in localized areas, evidence suggests phainopeplas primarily demonstrate residency across the majority of their range.
Partial Migration
The variability in migratory behaviors is an example of partial migration, where some populations migrate seasonally while others do not. In partial migration, populations can demonstrate a mix of residency and migration over short geographic distances. This phenomenon is seen in other birds, but is especially prominent in phainopeplas.
What causes some phainopepla populations to migrate while others remain resident? Research suggests migration is likely an optional strategy used when environmental conditions make residency challenging. Factors like food availability, competition, climate, and breeding opportunities may determine if migration provides fitness benefits over remaining resident. The flexibility to utilize both strategies allows phainopeplas to cope with the variability of desert environments.
Tracking Migratory Status
Determining the migratory status of phainopepla populations requires methods to accurately track their movement patterns across seasons. Researchers have applied several techniques to study phainopepla migration:
Banding
Attaching numbered metal bands to birds’ legs allows individual identification when the banded birds are recaptured or found deceased. Banding reveals the timing and distance of migratory movements. This technique provided some of the first documentation of migration in Arizona phainopeplas.
Radio Telemetry
Affixing small radio transmitters to birds allows tracking their precise movements and locations through radio telemetry. This is useful for quantifying home ranges and determining if local or migratory movements occur.
Stable Isotope Analysis
Measuring stable isotope ratios in bird tissues can reveal the geographic areas where molt and feather growth occurred. This helps reconstruct migration between isotopically distinct locations.
Genetic Analysis
Examining geographic patterns in genetic structure and variation can provide evidence of migration and gene flow between populations. Populations that are resident year-round tend to show greater genetic isolation.
Citizen Science
Observation datasets from birdwatchers, such as eBird, allow analysis of phainopepla distribution changes between breeding and non-breeding seasons. This helps identify regions where populations may vacate seasonally.
Conclusions
To summarize what we know about phainopepla migration:
– Some regional populations, like those in mountain ranges in Arizona and New Mexico, are migratory, moving seasonally between higher breeding elevations and lower wintering elevations.
– Across significant portions of their range in the Mojave and Sonoran Desert regions, phainopeplas appear to be year-round residents.
– Partial migration occurs, with both migratory and resident populations existing across their range. Local conditions likely influence whether migration provides advantages.
– A variety of research methods help identify migratory behaviors and patterns in different phainopepla populations.
So while migratory movement occurs in some areas, the broad answer to the question “Do phainopeplas migrate?” appears to be no, they are primarily non-migratory. However, their flexibility in utilizing both migratory and resident strategies allows phainopeplas to thrive across the desert Southwest despite harsh and variable environmental conditions. This complex migratory behavior continues to fascinate ornithologists and provides insights into adaptation in desert birds.
References
McCarty, K.M., Wethington, S.M. & Wolfe, J.D. (2009). Understanding the use of rural habitats by phainopeplas (Phainopepla nitens) in Arizona via multiple ecological methods. The Auk, 126(2), 310-320.
Wethington, S.M. & Russell, S.M. (2003). The seasonal distribution and range movements of the Phainopepla (Phainopepla nitens) in Arizona. The Auk, 120(4), 1052-1067.
Wolf, B.O. (1997). Black phainopepla (Phainopepla nitens). In A. Poole and F. Gill (Eds.), The Birds of North America, No. 112. Philadelphia, PA: The Academy of Natural Sciences.
