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Studies of variation in breeding parameters are often based on temporal analyses of a single population. However, to differentiate between the effects of regional and local factors, neighboring populations with limited interpopulational dispersal need to be compared. We studied two nearby (< 5 km apart) populations of House Wrens (Troglodytes aedon bonariae) at two ranches (Los Zorzales, 10 years; La Esperanza, 13 years) in south-temperate Argentina to assess the possible effects of regional and local factors on breeding phenology. For each breeding season, we recorded laying dates, clutch sizes, and length of the breeding season, and estimated the reproductive synchrony of first and second breeding attempts. We examined how these breeding parameters were affected by weather, population density, and rates of nest failure. With favorable temperatures during the pre-reproductive period (September–October), wrens in both populations initiated first breeding attempts earlier. However, ordinal laying dates were also affected by local factors, with wrens at Los Zorzales initiating breeding attempts earlier than those at La Esperanza. We found a spatial correlation in clutch sizes between populations for the 2007–2012 breeding seasons, but clutch sizes of first and second nesting attempts showed low variability. Reproductive synchrony of first nesting attempts varied among years, suggesting an effect of regional factors. However, we detected no synchronization between populations and were unable to identify environmental variables that explained the temporal variation. Ordinal laying dates of second clutches were strongly correlated with the ordinal laying dates of first clutches. We also found that the length of breeding seasons was longer when daily nest mortality rates were lower. Although environmental factors seemed to affect the decision of when to start breeding, pairs with successful first nesting attempts were more likely to initiate second nests, thus affecting the length of the breeding season. The spatial variation and temporal variation of the breeding parameters of House Wrens in our study provide evidence of marked plasticity in their breeding decisions and allowed us to identify local and regional environmental factors related to this variation. Los estudios de la variación de los paràmetros reproductivos se basan frecuentemente en el anàlisis de una unica población. Sin embargo, para diferenciar entre los efectos de los factores regionales y locales, se necesitan comparar poblaciones vecinas con limitada dispersión entre ellas. Nosotros estudiamos dos poblaciones cercanas (separadas por < 5 km) de Troglodytes aedon bonariae en el sur templado en Argentina (Los Zorzales, 10 años; La Esperanza, 13 años) para evaluar los posibles efectos de factores regionales y locales sobre su fenología reproductiva. En cada estación reproductiva registramos las fechas de puesta de las nidadas, el tamaño de la puesta y el largo de la temporada reproductiva, y estimamos la sincronía reproductiva de los primeros y segundos intentos reproductivos. Examinamos cómo esos parámetros reproductivos fueron afectados por la variacion del clima, la densidad poblacional y la tasa de falla de la nidificación. Con temperaturas pre-reproductivas (septiembre-octubre) favorables, los individuos de ambas poblaciones iniciaron las puestas más temprano. Sin embargo, las fechas de puestas de las nidadas fueron afectadas por factores locales, iniciando los individuos de Los Zorzales sus intentos reproductivos más tempranamente que aquellos de La Esperanza. Aunque encontramos una correlación espacial en el tamaño de las puestas entre las poblaciones durante las temporadas reproductivas de 2007–2012, los tamaños de puesta de los primeros y segundos intentos reproductivos demostraron una baja variabilidad. La sincronia reproductiva varió entre años, sugiriendo el efecto de factores regionales. Sin embargo, no detectamos una sincronización entre las poblaciones y no pudimos identificar las variables ambientales que explicasen la variación temporal. Las fechas de puesta de las segundas nidadas estuvieron fuertemente correlacionadas con las fechas de las primeras nidadas. Finalmente, la temporada reproductiva fue mós corta cuando las fallas en la nidificación fueron mas frecuentes. Mientras que los factores ambientales parecen afectar la decisión de cuándo iniciar la reproducción, el éxito de las primeras nidadas condiciona la decisión de iniciar una segunda nidada, afectando la duracion de la temporada reproductiva. La variacion especial y temporal de los paràmetros reproductivos de T. a. bonariae revelo la existencia de una marcada plasticidad en sus decisiones reproductivas y nos permitió identificar los factores locales y ambientales relacionados a esta variación.

Predation on vertebrate species by insect-eating birds is rarely recorded, with only one report for the House Wren (Troglodytes aedon). On 4 January 2019, we observed a Dominican House Wren (T. a. rufescens) consume a juvenile of the nonnative Puerto Rican crested anole (Anolis cristatellus) in Roseau, Commonwealth of Dominica. This observation suggests the Dominican House Wren could additionally prey on the endemic Dominican anole (Anolis oculatus). This record aids our understanding of the ecosystem-wide impact of the A. cristatellus invasion.

Measures of body condition, immune function, and hematological health are widely used in ecological studies of vertebrate populations, predicated on the assumption that these traits are linked to fitness. However, compelling evidence that these traits actually predict long-term survival and reproductive success among individuals in the wild is lacking. Here, we show that body condition (i.e., size-adjusted body mass) and cutaneous immune responsiveness to phytohemagglutinin (PHA) injection among neonates positively predict recruitment and subsequent longevity in a wild, migratory population of House Wrens ( Troglodytes aedon ). However, neonates with intermediate hematocrit had the highest recruitment and longevity. Neonates with the highest PHA responsiveness and intermediate hematocrit prior to independence eventually produced the most offspring during their lifetime breeding on the study site. Importantly, the effects of PHA responsiveness and hematocrit were revealed while controlling for variation in body condition, sex, and environmental variation. Thus, our data demonstrate that body condition, cutaneous immune responsiveness, and hematocrit as a neonate are associated with individual fitness. Although hematocrit's effect is more complex than traditionally thought, our results suggest a previously underappreciated role for this trait in influencing survival in the wild.

Human and animal populations increasingly encounter smoke pollution as climate change enhances the frequency and intensity of wildfires. Most work on smoke effects in animals has studied populations close to fires, populations experiencing small, prescribed burns, or animals in the lab. In June of 2023, smoke from distant Canadian wildfires quickly elevated particulate matter (PM 2.5 ) pollution in a wild house wren ( Troglodytes aedon ) population for three days before returning to baseline levels. Compared to previous years, nestlings experiencing three days of elevated PM 2.5 within the first 6 days of life weighed less on days 6 and 10 after hatching and had shorter tarsometatarsus bones, a sign of smaller skeletal size. In contrast, nestlings that hatched before or after this event did not differ in size from previous years. Although sublethal, these effects may have important consequences for survival and reproduction. As wildfire activity increases, more wildlife populations are at risk of smoke-related fitness consequences, even those distant from the blaze.

Many bird species vary their alarm calls according to the level of risk they face and this information can be used by receivers to respond to the mobbing event. Recent studies have also found that the number of callers can play an important role in the decision of subsequent individuals to join a mobbing event. We conducted a playback experiment to assess if differences in calling rate and number of callers elicit different behavioural responses in the house wren (Troglodytes aedon chilensis). We broadcast the alarm call of either one or two individuals, at different calling rates along the breeding season. We found that house wrens responded more frequently during playback of alarm calls at higher rates than during playback of calls at lower rates. However, focal individuals moved closer to the speaker when calls were played back at lower rates. There were no differences in the response of house wrens when we broadcast the calls of one or two individuals. These results suggest that call rates are an important element in the communication of danger in the house wren, rather than caller number.Significance statementMobbing is an anti-predator strategy observed in many species, and often involves the use of calls that can communicate to conspecifics and heterospecifics about the threat of the predator. Understanding the factors and cues that receivers use to respond is an important element in understanding communication between individuals. We studied the role of call rate and number of callers in the behavioural response to mobbing calls of individuals in the house wren during the breeding season. Using a playback experiment, we show that individuals respond more often to calls played at a high rate, regardless of the number of callers. House wrens' call rates vary according to the level of perceived risk, so our results show that receivers use this information to respond to mobbing calls.

Abstract Nesting house wrens (Troglodytes aedon bonariae) use two basic alarm calls (Type I and Type II) when detect a threat near the nest. We experimentally analysed if calls distract predators or serve to recruit other birds to create a mobbing flock to deter predators. The results show that individuals preferentially position themselves in front of the threat, disclosing the location of the nest. Also, using playbacks of house wren alarm calls we found that these calls recruited both conspecific and heterospecific individuals to create a mobbing response. The alarm calls of house wrens seem to fulfil multiple functions, not only conveying information about the threat to their mates and nestling as revealed in previous studies, but also as a signal that attracts the attention of other conspecific and heterospecific individuals and can trigger a mobbing response to deter the predator.

Cryptic genetic differentiation is being increasingly documented in birds and other organisms using genome‐wide variation. A recent example of cryptic genetic differentiation in a widespread species with conserved morphology is the northern house wren Troglodytes aedon. We found that, despite extremely similar morphology and no documented vocal differences, the two subspecies of the northern house wren, T. a. aedon (eastern) and T. a. parkmanii (western), exhibited both nuclear and mitochondrial genomic differentiation. Individuals present along the Front Range of the Colorado Rocky Mountains possessed nuclear genetic variation intermediate between T. a. aedon and T. a. parkmanii; additionally, both divergent mitochondrial lineages, corresponding to the western and eastern northern house wren populations, occur in Colorado. However, the dynamics of this putative contact zone (i.e. amount of hybridization or introgression) and the degree of differentiation between the two subspecies remain uncharacterized. To expand our understanding of northern house wren population genetic differentiation and explore the possibility of hybridization, we used a double digest restriction‐site associated (ddRAD) approach and sequenced 127 northern house wrens, including 109 individuals from across Colorado and Wyoming, as well as nine individuals each from eastern and western allopatric regions. Our results highlight that T. a. aedon occur significantly further west than previously thought, and provide evidence for weak population structure within the northern house wren, while generally setting the stage for future investigations of northern house wren population genomics and the genetic basis of cryptic speciation.

Climate change has affected the seasonal phenology of a variety of taxa, including that of migratory birds and their critical food resources. However, whether climate-induced changes in breeding phenology affect individual fitness, and how these changes might therefore influence selection on breeding date remain unresolved. Here, we use a 36-yr dataset from a long-term, individual-based study of House Wrens (Troglodytes aedon) to test whether the timing of avian breeding seasons is associated with annual changes in temperature, which have increased to a small but significant extent locally since the onset of the study in 1980. Increasing temperature was associated with an advancement of breeding date in the population, as the onset of breeding within years was closely associated with daily spring temperatures. Warmer springs were also associated with a reduced incubation period, but reduced incubation periods were associated with a prolonged duration of nestling provisioning. Nest productivity, in terms of fledgling production, was not associated with temperature, but wetter springs reduced fledging success. Most years were characterized by selection for earlier breeding, but cool and wet years resulted in stabilizing selection on breeding date. Our results indicate that climate change and increasing spring temperatures can affect suites of life-history traits, including selection on breeding date. Increasing temperatures may favor earlier breeding, but the extent to which the phenology of populations might advance may be constrained by reductions in fitness associated with early breeding during cool, wet years. Variability in climatic conditions will, therefore, shape the extent to which seasonal organisms can respond to changes in their environment.

Secondary cavity-nesting species must find natural cavities or artificial nest boxes to reproduce. Cavities are often limited, which results in intense interference competition among species that rely on them. Nest site shortages may exclude subordinate individuals from cavities and force them to adopt alternative reproductive tactics such as laying eggs in the nests of conspecifics or in the nests of other species. The Prothonotary Warbler (Protonotaria citrea) is a secondary cavity-nesting bird that opportunistically parasitizes conspecifics that has never been recorded parasitizing heterospecifics. Here, we report brood parasitism of a House Wren (Troglodytes aedon) nest by a Prothonotary Warbler and the subsequent fledging of a warbler from this nest. This is the first observation of interspecific brood parasitism for the Prothonotary Warbler and the first instance of interspecific brood parasitism by any New World warbler species. Especies que anidan en cavidades secundarias deben encontrar cavidades naturales o cajas nido artificiales para reproducirse. Las cavidades son usualmente limitadas, lo que resulta en una intensa competencia por interferencia entre especies que dependen de ellas. La escasez de sitios de anidamiento puede excluir individuos subordinados de las cavidades y obligarlos a adoptar estrategias reproductivas alternativas como poner huevos en nidos de conespecíficos o en nidos de otras especies. La reinita Protonotaria citrea es una ave que anida en cavidades secundarias que parasita oportunisticamente a conespecíficos pero que nunca ha sido grabada parasitando a heteroespecíficos. Aquí reportamos parasitismo de nidada en un nido de saltapared Troglodytes aedon por una reinita Protonotaria citrea y el subsecuente emancipamiento de una reinita de ese nido. Esta es la primera observación de parasitismo de nidada interespecífico por la reinita Protonotaria citrea y la primera instancia de parasitismo de nidada interespecífico por alguna especie de reinita del Nuevo Mundo. Palabras clave: nido en cavidad, saltapared, Troglodytes aedon.

Many avian species persist in human-dominated landscapes; however, little is known about the demographic consequences of urbanization in these populations. Given that urban habitats introduce novel benefits (e.g., anthropogenic resources) and pressures (e.g., mortality risks), conflicting mechanisms have been hypothesized to drive the dynamics of urban bird populations. Top-down processes such as predation predict reduced survivorship in suburban and urban habitats, whereas bottom-up processes, such as increased resource availability, predict peak survival in suburban habitats. In this study, we use mark-recapture data of seven focal species encountered between 2000 and 2012 to test hypotheses about the processes that regulate avian survival along an urbanization gradient in greater Washington, D.C., USA. American Robin, Gray Catbird, Northern Cardinal, and Song Sparrow exhibited peak survival at intermediate and upper portions of the rural-to-urban gradient; this pattern supports the hypothesis that bottom-up processes (e.g., resource availability) can drive patterns of avian survival in some species. In contrast, Carolina Chickadee showed no response and Carolina and House Wren showed a slightly negative response to urban land cover. These contrasting results underscore the need for comparative studies documenting the mechanisms that drive demography and how those factors differentially affect urban adapted and urban avoiding species.