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Much attention has been paid to the impacts of plastics and other debris on marine organisms, but the effects of plastic on terrestrial organisms have been largely ignored. Detrimental effects of terrestrial plastic could be most pronounced in intensively human-modified landscapes (e.g., urban and agricultural areas), which are a source of much anthropogenic debris. Here, we examine the occurrence, types, landscape associations, and consequences of anthropogenic nest material in the American crow (Corvus brachyrhynchos), a North American species that breeds in both urban and agricultural landscapes. We monitored 195 nestlings in 106 nests across an urban and agricultural gradient in the Sacramento Valley, California, USA. We found that 85.2% of crow nests contained anthropogenic material, and 11 of 195 nestlings (5.6%) were entangled in their nests. The length of the material was greater in nests in agricultural territories than in urban territories, and the odds of entanglement increased 7.55 times for each meter of anthropogenic material in the nest. Fledging success was significantly lower for entangled than for unentangled nestlings. In all environments, particularly urban, agricultural, and marine, careful disposal of potential hazards (string, packing and hay bale twine, balloon ribbon, wire, fishing line) could reduce the occurrence of entanglement of nestling birds.

Between 26 and 28 June 2021, the United States' Pacific Northwest endured an unprecedented heatwave that broke previous temperature records by 5 °C. Here, we report the impacts of the heatwave on Bushtit (Psaltriparus minimus) nests being monitored as part of a long-term study in Portland, Oregon. Of the 8 nests active during the event, nestling mortality was 100% in 3 nests and 4 broods survived at least in part. We suspect the excessive heat forced at least one additional brood to fledge early. Remains of nestlings found in 2 nests that eventually fledged suggest that even those encountered brood reduction during the heatwave. Nests with broods that survived were closer to a water source (x̄=13 m) than nests with broods that did not survive (x̄ = 148 m). In addition, surviving broods were younger (either eggs or <4 d of age) than those that perished (>9 d of age). Since these are only the second incidence of total nestling mortality other than depredation observed during Sloane's long-term research on Bushtits in Oregon and Arizona (1986–present), we consider this to be a significant finding and indicative of the future negative effects of global climate change on temperate zone species of breeding passerines.

We sequenced the mitochondrial ND2 gene for 290 Bushtits (Psaltriparus minimus) sampled from northern Washington to Guatemala. Phylogenetic analysis sorted specimens into 2 main lineages residing either west (coastal) or east (inland) of the Sierra Nevada and Cascades. These lineages are separated by 3.5% sequence divergence and correspond with the distributions of 2 long-recognized phenotype groupings (brown-capped and plumbeous, respectively). Three additional monophyletic geographically structured lineages were identified. Birds from southmost Baja California (Sierra de la Laguna) segregate from other coastal samples whereas the inland lineage includes additional lineages occurring in southeastern Mexico (Morelos, Puebla, Guerrero, and Oaxaca) plus Guatemala, and southwestern Mexico (Michoacán). Examination of museum specimens revealed that a black-eared phenotype occurs sporadically in the interior lineage in southern U.S. and northern Mexico, increasing in frequency to the south, corresponding roughly with these southern Mexican mtDNA lineages. Degree of sequence divergence between the 2 main lineages suggests a relatively early divergence, and ample time for 2-way introgression to occur. However, only 1 of our sampling localities (Lake Co., Oregon; n = 4) was mixed for coastal (n = 1) and interior (n = 3) lineages suggesting the possibility of reproductive isolation between the 2 main lineages. Secuenciamos el gen mitocondrial ND2 de 290 mitos colectados desde el norte de Washington hasta Guatemala. Los análisis filogenéticos clasificaron a los especímenes en 2 linajes principales que residían ya sea en al oeste (costero) o al este (interior) de la Sierra Nevada y Cascades. Estos linajes se separan por una divergencia de secuencias de 3.5% y corresponden a distribuciones de 2 agrupamientos fenotípicos reconocidos desde hace mucho tiempo (respectivamente capucha marrón y plomizo). Se reconocieron tres linajes adicionales monofiléticos estructurados geográficamente. Aves de la parte más sureña de Baja California (Sierra de la Laguna) se segregan de otras muestras costeras mientras que linajes del interior incluyen otros linajes que se encuentran en el sudeste mexicano (Morelos, Puebla, Guerrero y Oaxaca), sumado a Guatemala y al sudoeste mexicano (Michoacán). La examinación de especímenes de museo reveló que un fenotipo de oreja negra se encuentra esporádicamente en el linaje interior en el sudeste de Estados Unidos y norte de México, que aumenta su frecuencia hacia el sur y corresponde en general con linajes mtADN del sudeste mexicano. El grado de divergencia de secuencias entre los 2 linajes principales sugiere una divergencia relativamente temprana y un tiempo grande para que ocurriera una introgresión de 2 vías. Sin embargo, solo una de las localidades de muestreo (Lake Co., Oregon, n = 4) presentaba una mezcla de linajes costero (n = 1) e interior (n = 3), sugiriendo la posibilidad de aislamiento reproductivo entre los 2 linajes principales. Palabras clave: ADN mitocondrial, árbol genético, divergencia de linaje, filogeografía, modelos de nicho.

We recorded Bushtit (Psaltriparus minimus) flock size on the Seattle University campus across multiple seasons in order to characterize the timing of pair formation prior to nest building in Washington state and compare it to that of California and Arizona. We also collected autumn and winter foraging locations, specifically vegetation types and foraging heights. We found the disbanding of large flocks (15–20 birds) into nest-building pairs occurred 1–2 months later in the northern part of the Bushtit's range than what is reported in more southern states. Bushtits spent a similar percentage of time foraging in deciduous trees, evergreen trees, and mixed shrubs in fall and winter, often moving along garden strips at heights of 3–4.5 m off the ground. Contrary to published reports, groups of Bushtits repeatedly visited fixed food sources, specifically the yellow flowers of the exotic leatherleaf mahonia (Mahonia bealei) for over 2 weeks on early winter mornings.

Plasticity in bird nest placement is relatively understudied compared to many other aspects of breeding biology. We describe an unusual nest of a Bushtit (Psaltriparus minimus) that was placed inside an old woodpecker cavity instead of being attached to the foliage of a tree or shrub. A pair of Bushtits successfully fledged one brood inside this cavity and then immediately constructed a second nest in the same cavity. Concurrent with this second nesting effort, a Tree Swallow (Tachycineta bicolor) actively competed with the Bushtits for the same cavity and was seen nest building in the cavity as well. The apparent rarity of cavity nesting by the Bushtit suggests this nesting effort was serendipitous and perhaps facilitated by the dimensions of the cavity, which were similar to the hanging, pendulous nest this species typically builds.

Recent experiments support the long-standing hypothesis that Common Cuckoos (Cuculus canorus) are mimics of Eurasian Sparrowhawks (Accipiter nisus). Additional experiments further suggest that mimicry benefits the cuckoos by reducing the intensity of mobbing they suffer near host nests, at least in some host populations, potentially increasing their access to the hosts' nests. We observed two species of birds—one very rarely parasitized and the other never parasitized by cuckoos—responding to a cuckoo as they would a bird of prey. On the island of Öland, Sweden, we observed two instances of a gray phase cuckoo being mobbed by a group of Barn Swallows (Hirundo rustica) during the non-breeding season. These mobbing observations cannot be explained as a consequence of selection in the context of brood parasitism, because swallows are extremely rare cuckoo hosts and should not show co-evolutionary responses to parasitism. Instead, the swallows appear to have mistaken the cuckoos for Eurasian Sparrowhawks and responded as they would to true hawks. Similar observations were made in California, where a vagrant Common Cuckoo repeatedly elicited alarm calls from Bushtits (Psaltriparus minimus), a species completely allopatric with cuckoos and thus with no evolutionary history of brood parasitism. Because Eurasian Sparrowhawks visually resemble related North American bird-eating Accipiter hawks in plumage and flight characteristics, the cuckoo likely triggered a general Accipiter response in the Bushtits. Together, these observations provide additional evidence that cuckoos successfully mimic Eurasian Sparrowhawks and that such mimicry comes not only with benefits to the cuckoos, but costs as well.

There is a growing body of literature covering the responses of bird species to wildland fire events. Our study was unique among these because we investigated the effects of large-scale wildland fires on entire bird communities across multiple vegetation types. We conducted avian point counts during the breeding seasons for two years before and two years after the Cedar and Otay Fires in 2003 in southern California. Our balanced sampling effort took place at two sites, one low-elevation and one high-elevation, each containing replicate stations (burned and unburned) within five vegetation types: chaparral, coastal sage scrub, grassland, oak woodland, and riparian. Although fire caused some degree of change in the vegetation structure at all of our impacted survey points, we found that the post-fire shrub and tree cover was significantly lower in only two of the vegetation types within the low-elevation site, coastal sage scrub and chaparral. We found no significant changes in cover at the high-elevation site. Using univariate and multivariate analyses, we tested whether the fires were associated with a change in bird species diversity, community structure, and the relative abundance of individuals within a species. We found that species diversity changed in only one circumstance: it increased in coastal sage scrub at the low-elevation site. Multivariate analyses revealed significant differences in the post-fire bird community structure in the low-elevation chaparral, low-elevation coastal sage scrub, and the high-elevation grassland communities. Vegetation characteristics altered by fire, such as decreases in shrub and tree cover, influenced the changes we observed in the bird communities. The relative abundance of some species (lazuli bunting [Passerina amoena] and horned lark [Eremophila alpestris]) significantly increased after the fires, while other species declined significantly (Anna's hummingbird [Calypte anna], wrentit [Chamaea fasciata], and bushtit [Psaltriparus minimus]). We detected mixed results for the spotted towhee (Pipilo maculatus), which increased in burned chaparral and declined in burned coastal sage scrub within the low-elevation site. We suggest that the observed responses of birds to these fires may be attributed to: (1) the availability of nearby unburned refugia, (2) the continued suitability of post-fire vegetation at the study sites, and (3) the generally high mobility of this taxon.

I studied a color-banded population of Bushtits (Psaltriparus minimus) in the Chiricahua Mountains of southeastern Arizona from 1986 through 1991. Overall, 37% of nests had one to four supernumerary birds, most of which were adult males. Indirect and direct evidence suggested that most supernumeraries were males that had not acquired a mate, or were failed breeders of either sex. Sex ratios were consistently skewed in favor of males, although males almost always were associated with a nest, and years in which nest loss was high had a correspondingly high incidence of multibird (>2 bird) nests. Some supernumeraries may have contributed genetically to the contents of nests they attended, either by laying eggs or by mating with the female, resulting in possible polygynous, polyandrous, and polygynandrous groups. I suggest that a primary route to multibird nests in Bushtits is via competition for existing nests and mates. Birds without nests (individuals or pairs) attempt to evict the residents and, if unsuccessful, sometimes compromise and join as helpers or additional breeders.

Multilocus DNA fingerprinting was used to investigate parentage in a population of bushtits in the Chiricahua Mountains. In the breeding season studied, the bushtits were sexually monogamous and exhibited no egg-dumping behavior.