Search

Birds commonly adjust timing of breeding to spring temperatures. Wc examine 40 years of data from the Owyhee Mountains of southern Idaho to determine whether mean lay date of Mountain Bluebirds (Sialia currucoides) is associated with May temperatures and whether an increase in those temperatures has advanced the breeding phenology of this species. Average May temperatures increased by 2.20[degrees]C (CI = 0.58, 3.82) from 1980 to 2019, were negatively correlated with the mean lay date of Mountain Bluebirds, and thus were associated with an advancement in breeding phenology of 2.09 (CI =1.16, 3.03) days per decade. Our study demonstrates the importance of long-term monitoring to detect effects of climate change on bird phenology. Received 14 November 2022. Accepted 11 September 2023. Key words: climate change, community science, global warming, Idaho, phenology., Las aves usualmente ajustan su epoca de reproduccion a las temperaturas de primavera. Examinamos 40 aflos de datos de Owyhee Mountains del sudeste de Idaho para determinar si la fecha [...]

Studies on the migratory behavior of songbirds are important to inform full annual cycle conservation. We remotely tracked the early fall migratory movements of both juvenile and adult Savannah Sparrows (Passerculus sandwichensis) that were tagged on their natal breeding territories in southwestern Ontario, Canada, where the Motus Wildlife Tracking System has the highest density of automated receivers in North America. Our primary aims were to describe and compare adult and juvenile migratory movements during the early part of migration, compare frequency of detection of juveniles versus adults as a proxy for minimum apparent survival, and describe potential migration routes and overwintering areas. Juveniles initiated migration approximately a month earlier than adults. Both juveniles and adults typically made their first migratory flight in a southwest direction, but some juveniles displayed subsequent exploratory movements that were not in a southwest direction, potentially to collect information for next year's breeding site selection. Detection rates early in migration were similar, but low. for adults and juveniles (34% and 39% respectively), suggesting that juveniles that had survived the fledgling period likely did not experience high mortality during the subsequent 2 months prior to their fall migration. Long-distance detections of 2 adults preliminarily suggest that individuals from this southern Ontario breeding region may travel west of the Appalachian Mountains along the Mississippi flyway during fall migration. Our study aligns with previously reported patterns of age-specific migratory behavior from other Savannah Sparrow populations and contributes to our overall understanding of the migratory ecology of this species. Received 6 April 2021. Accepted 23 September 2022. Key words: fall migration, migration orientation, migration timing, songbird, telemetry. Los estudios de comportamiento de ave migratorias son importames para conocer su ciclo anual completo de conservacion. Monitoreamos de manera remota los movimientos migratorios de otofio temprano tanto de juveniles como de adultos de gorrion Passerculus sandwichensis que fueron marcados en sus territories natales/ reproductivos en el sudoeste de Ontario. Canada, donde el Sistema de Monitoreo de Vida Silvestre Motus tiene la mayor densidad de receptores automaticos de Norteamerica. Nuestros objetivos primarios ilieron describir y comparar los movimientos migratorios de adultos y juveniles durante !a parte inicia! de la migracion. comparar la frecueneia de deteccion de juveniles versus de adultos como proxy de la sobrevivencia aparente minima asi como describir potenciales rutas migratorias y areas de hibernacion. Los juveniles iniciaron la migracion aproximadamente un mes antes que los adultos. Tanto juveniles como adultos tipicamente hicieron su primer vuelo migratorio en direccion sudoeste. aunque algunos juveniles desplegaron movimientos exploratorios posteriores que no eran en direccion sudoeste. posiblemente para coleetar informacion para la seleccion del sitio de reproduccion del afio siguiente. Las tasas de deteccion de migracion temprana rueron similares. aunque bajas. para adultos y juveniles (respectivamente 34% y 39%), lo que sugiere que tos juveniles que sobrevivieron a su etapa de volantones posiblemente no tuvieron una alta mortalidad durante los 2 meses que siguieron a la migracion otonat. La deteccion a larga distancia de 2 adultos sugiere preliminarmente que los individuos de esta region de reproduccion al sur de Ontario podrian viajar al oeste de las Appalachian Mountains a lo largo del rio Mississippi durante la migracion de otono. Nuestro estudio se alinea con patrones previamente reportados de patrones migratorios especificos por edad de otras poblaciones de gorrion Passerculus sandwichensis y contribuyen al entendimiento general de la ecologia migratoria de esta especie. Palabras clave: aves canoras. migracion otonal, orientacion migratoria. telemetria, tiempo migratorio., The miniaturization of archival tracking devices has allowed scientists to directly follow the movements of individual migrating birds to determine their behavior and overwintering areas (McKinnon and Love 2018), leading [...]

An important goal of urban ecology is determining what differentiates urban-tolerant populations of birds from their non-urban ancestors and urban-intolerant species. One key to urban success may be reacting appropriately to human activity, and the degree to which birds view humans as threats can be quantified by their escape behavior. Understanding individual-level plasticity, however, requires the tracking of known individuals. We compared flight-initiation distances (FID) and distances fled (DF) from approaches by a human between an urban and a non-urban population of individually marked Dark-eyed Juncos (Junco hyemalis) in Southern California. The urban population is more tolerant to people as evidenced by attenuated FIDs and DFs relative to non-urban birds. Although individual urban birds either habituated or sensitized to repeated approaches, there was no significant pattern at the population level. Overall, the behavioral patterns exhibited by this urban population of juncos is more supportive of in situ evolution of tolerance than either being a biased sample from an ancestral non-urban population or intrinsic behavioral plasticity that produces a uniform adjustment to urban life. Received 10 December 2020. Accepted 7 December 2021. Key words: anti-predator behavior, avian, fleeing, flight-initiation distance, urban ecology. (Spanish)--Un objetivo principal en el estudio de ecologia urbana es identificar las diferencias entre poblaciones de aves urbanas con poblaciones ancestrales no-urbanas o poblaciones que no toleran cl ambiente urbano. Una clave para su exito urbano cs la manera en que las aves reaccionan a la actividad humana y el grado en que las aves se sienten amenazadas por la presencia humana puede ser cuanlificada por su coinportamiento de escape. Para tener un conoeimiento fundamental sobre la plasticidad a nivel individual, se requiere el seguimiento de individuos marcados. Nosotros comparamos la distancia de iniciacion al vuelo (FID) y la distancia de huida (DF) de acercamientos por humanos entre poblaciones urbanas y no-urbanas de junco de ojos oscuros (Junco hyemalis) en el sur de California. Segun las FIDs y DFs que medimos, encontramos que individuos de la poblacion urbana pueden tolerar la presencia humana mas que la poblacion no-urbana. Aunque encontramos individuos que son tolerantes o vulnerables a los multiples acercamientos humanos, no encontramos un patron significativo a nivel de poblacion. En conjunto, los patrones de comportamiento mostrado por los juncos urbanos apoyan la evolucion en situ, en vez de apoyar una muestra sesgada de una poblacion ancestral no urbana ni la plasticidad conductual intrinscea que produce un ajustc uniforme a la vida urbana. Palabras clave: aviar. comportamiento anti-depredador. distancia de inicio de vuelo. ecologia urbana, escape., Urbanization creates both costs and benefits across bird species. Some species thrive in urbanized settings due to factors such as feeders providing abundant and stable food supplies (Reynolds et al. [...]

This study presents the first description of the breeding biology of the IUCN Endangered North Philippine Hawk-Eagle (Nisaetus philippensis). We describe a single pair's breeding phenology, nest characteristics, diet, chick development, and behavior through on-the-ground and remote observations from 1 February to 14 May 2020. Due to limited mobility during the COVID-19 pandemic, we improvised a video recording setup for remote monitoring and used machine learning to extract data from images. The nest was a low cup/fork type stick nest placed on a Malabulak tree (Bombax ceiba) in a heavily disturbed secondary forest. When it was first found, the incubation stage was underway and lasted for 1 month as the nestling emerged on 1 March 2020. Both adults provided parental care throughout the breeding period, with the male primarily providing food and the female attending to the nest, egg, and chick. They preyed on a wide range of vertebrates such as lizards, ground birds, bats, rodents, and domestic animals. With a single egg per clutch and a relatively long breeding cycle, the species has a slow reproductive output that may contribute to its current threatened status. Received 10 February 2021. Accepted 7 December 2021. Key words: Asian raptors, chick development, nest monitoring, parental care, threatened raptor. (Filipino)--Makikita sa pag-aaral na ito ang unang paglalarawan ng biolohiya ng pag-aanak ng IUCN Endangered na North Philippine Hawk-eagle (Nisaetus philippensis). Inilarawan namin ang penolohiya ng pag-aanak, katangian ng pugad, karaniwang pagkain, paglaki ng sisiw, at pagkilos ng isang pares ng magulang sa pamamagitan ng obserbasyon mula 1 Pcbrero hanggang 14 Mayo 2020. Dahil sa limitadong mobilidad sa panahon ng pandcmyang COVID-19. nag-improbisa kami ng video recording setup para sa tnalayuang pagsubaybay at gumamit ng machine learning para makakuha ng datos mula sa mga imahe. Ang pugad ay isang low cup o fork type na gawa sa mga patpat at nakapatong sa isang punong Malabulak (Bombax ceiba) sa isang seknndaryong gubat malapit sa mga tao. Nang una itong natuklasan. nakapagsimula na ang yugto ng pagfilimlim na tumagal ng isang buwan. Lumabas ang sisiw noong 1 Marso 2020. Inalagaan ng dalawang magulang ang sisiw sa buong panahon ng pag-aanak, ang lalaki ang pangunahing naghanap ng pagkain samantalang ang babae ang nagbantay sa pugad, itlog, at sisiw. Kumain sila ng iba't ibang uri ng vertebrates katiilad ng mga bayawak, tikling, paniki, daga, at domcstikong hayop. Dahil paisa-isa lamang ang kanilang pangingitlog at may kahabaan ang siklo ng pag-aanak, matagal ang proseso ng pagpapalahi nila na maaaring isa sa mga dahilan kung bakit ito nanganganib ngayon. Susing salita: ibong-mandaragit ng Asya, nanganganib na ibong-mandaragit, pag-alaga ng magulang ibon, paglaki ng sisiw, pagsubaybay ng pugad., The North Philippine Hawk-Eagle (Nisaetus philippensis) is an IUCN Endangered raptor endemic to Luzon and Mindoro Island, Philippines (Allen 2020). The population is in decline with a global estimate of [...]

We monitored the emergence of cooperative breeding behavior in 2 Brown-headed Nuthatch (Sitta pusilla) populations that were reintroduced to formerly occupied sites in south Florida. Individuals from presumed family groups were captured and moved (n = 48) in the first reintroduction attempt (1998-2001) an Everglades National Park, Florida, USA. Two cooperative breeding groups were observed in the second breeding season (2000) and the proportion of cooperative breeding groups increased to -20% of the territories present in year 5. The second reintroduction attempt focused on capture and release of juveniles (n = 30) onto Jonathan Dickinson State Park. Florida, USA. A cooperative breeding group was observed in the first breeding season (2019) of this second attempt and in the 2 breeding seasons that followed (20202021). Cooperative breeding behavior was observed in both reintroduction attempts when nuthatches occupied a small fraction of the available habitat. Habitat saturation has been linked to cooperative breeding behavior in other avian taxa, but our observations point to the potential influence of other factors in promoting cooperation in the nuthatch. Recent studies suggest these factors might include mate limitations, benefits derived from group activities, and direct benefits of co-breeding among >2 adults. Received 30 November 2019. Accepted 4 October 2021. Key words: collective actions, habitat saturation, mate limitations, reintroduction. El comportamiento cooperativo de anidacion emerge pronto en poblaciones restauradas del trepador Sitta pusilla Dimos scguimiento a como emerge el comportamiento cooperativo de anidacion en 2 poblaciones del trepador Silta pusilla que fucron reintroducidas en sitios previamentc ocupados en el sur de Florida. Individuos presumiblementc de grupos familiarcs fucron capturados y translocados (n = 48) en el primer intcnto dc reintroduccion (1998-2001) en el Everglades National Park. Florida, EUA. Dos grupos cooperatives de anidacion fueron obscrvados en la segunda temporada reprodnctiva (2000) y la proporcion de grupos cooperatives de reproduccion se increment!) -20% de los territorios presentes en el ano 5. El segundo intento de rcintroduccion se enfoco en la captura y liberacion de juveniles (n = 30) en el Jonathan Dickinson State Park, Florida, EUA. Un grupo cooperative de anidacion se observo en la primera temporada reproductiva (2019) de este segundo intento y en las 2 temporadas reproductivas subsiguicntes (2020-2021). El comportamiento coopcrativo de anidacion t'ue observado en ambos intentos de reproduccion cuando los trcpadores ocuparon una pequefta fraccion del habitat disponiblc. La saturacion del habitat ha sido vinculada al comportamiento coopcrativo dc anidacion en otros taxa de aves, aunquc nucstras obscrvaeioncs scftalan la posiblc influencia de otros factores en promovcr la cooperacion en el trepador. Estudios recientes sugieren que cstos factores podrian incluir limitacion de parejas. beneficios derivados de actividades gaipales y beneficios directos de la co-reproduccion entre >2 adultos. Palabras clave: accioncs colectivas, limitaciones de pareja, reintroduccion, saturacion de habitat., Cooperative breeding is uncommon among birds and features the presence of adults that appear to forego opportunities for independent breeding and paradoxically assist in the reproductive efforts of other adults [...]

Understanding how diet and life history strategies interact is important for exploring constraints of available nutrition on energetically expensive life history events in wild animals (i.e.. reproduction, annual migration, molt). Previous research on migratory birds breeding in the Northern Hemisphere has demonstrated trophic niche shifts from invertebrates to fruit in order to fuel spring migration. We examined whether a trophic niche shift occurred in a Neotropical austral migrant, the Fork-tailed Flycatcher (Tyrannus savana savana), prior to spring migration by measuring stable nitrogen isotopes in feathers. We found that the austral migrant subspecies T. s. savana did appear to shift in diet from a higher to a lower trophic level (consistent in pattern with a shift from a higher to a lower ratio of invertebrates to fruit) but the shift occurred earlier than expected if it was preparation for migration. A sympatric sedentary subspecies occupying the same habitat (T. s. monachus) appeared to forage only at the lower trophic level during its annual molt and showed no evidence of a trophic niche shift; however, the molt of the 2 subspecies occurs at slightly different times of year. The timing of the trophic niche shift leads us to conclude that a higher trophic level diet early in molt is not related to preparation for spring migration but that it may be related to seasonal changes in food availability as the wet season concludes. A remaining challenge for understanding the ecological consequences of trophic niche shifts is to find ways to empirically measure trade-offs between different diets across energetically expensive life history events and compare these between taxa with differing life history strategies. Received 2 December 2020. Accepted 8 October 2021. Key words: flycatcher, migratory ecology, stable nitrogen isotope analysis. Mudanca de nicho trofico em um migrante da America do Sul: assinatura de isotopo estavel de nitrogenio em penas da tesourinha (Tyrannus savana) Compreender como a dieta e estrategias de historia dc vida interagem e importante para explorar limitacoes de disponibilidade nutricional cm eventos de historia de vida energeticaniente custosos em animais selvagens (i.e., reproducao, migracao anual, muda). Estudos anteriores em aves migratorias que se reproduzem no hemisferio norte demonstraram mudancas de nicho trofico, de invertebrados para frutos. para abastecer a migracao de primavera. Nos examinamos se a mudanca de nicho trofico ocorreu em um migrante austral neotropical, a tesourinha (Tyrannus savana savana), antes da migracao de primavera medindo iscitopos estaveis de nitrogenio nas penas. Nos encontramos que a subespecie migratoria austral T. s. savana aparcnta modifies sua dieta de unt nivel trofico mais alto para um mais baixo (consistente com um padrao de mudancas de uma dicta com alta proporcao de invertebrados para uma rica em frutos) mas essa mudanca ocorrcu mais eedo do que o esperado se ela fosse uma preparacao para a migracao. Uma subespecie simpatrica sedentaria que ocupa o mesmo habitat (T. s. monachus) aparentou Ibrragear apenas em niveis troficos mais baixos durante sua muda anual c nao moslrou evidencias de uma mudanca trofica. Entretanto, a muda dc ambas as subespecies ocorreu em pcriodos ligeiramente distintos do ano. O momento da mudanca de nicho trofico nos leva a concluir que dietas baseadas em nivel trofico mais alto no inicio da muda nao se relaciona com a preparacao para a migracao de primavera. mas pode se relacionar com mudancas sazonais na disponibilidade de alimentos a medida cm que a estacao umida se encerra. Um desafio remanescente para compreendcr as consequencias ecologicas de mudancas de nicho trofico c encontrar modos para medir empiricamente as demandas conflitantes dc difercntes dietas cntre eventos de historia de vida energcticamente custosos e compara-las cntre taxa com diferentcs eslrategias de historia de vida. Palavras-chave: analises de isotopos estaveis de nitrogenio, eeologia migratoria. papa-moscas., One of the most critical parts of the annual cycle of migratory birds is the preparation for spring migration because properly timing arrival on the breeding grounds is a key [...]

Polygamy is common in many taxa, particularly birds. Several hypotheses support evolutionary or ecological explanations for the presence of polygamous mating systems, but these may not explain rare occurrences of polygamy in predominantly monogamous systems. We identified 12 cases of polygyny in 3 populations of varying landscape structure (contiguous wildlands. fragmented wildlands, and suburban) across 97 years of collective study on the monogamous Florida Scrub-Jay (Aphelocoma coerulescens). We categorized each case based on social similarities and compared reproduction between monogamous family groups and polygynous males and females. We found no difference in the relative rate of polygyny across the 3 populations. Neither presence of helpers, annual helper sex ratio, or breeder female survival were associated with polygyny occurrence. Reproductive output was similar between polygynous and monogamous males, but significantly lower for polygynous versus monogamous females. Polygyny in Florida Scrub-Jays appears to occur under certain social contexts but is rare even as those contexts are not. Neither sex appears to benefit from polygynous matings but forming a polygynous triad may be better than forgoing breeding. Received H June 2020. Accepted I October 2021. Key words: cooperative breeding, mating systems, monogamy, polygyny, sexual conflict. La poligamia es comiin en machos taxa. particularmente en las aves. Varias hipdtesis dan soportc a explicaciones evolutivas o ccologicas a la presencia dc sistemas de apareo poligamos. si bien estas no dan expliean eventos de poligamia en sistemas preponderantemcnte monogamos. Idcntilicamos 12 casos de poliginia en 3 poblaciones de estructura de paisaje variadas (areas silvestres contiguas. areas silvestres fragmentadas y suburbano) a lo largo de 97 anos de trabajo colectivo en la urraca monogama Aphelocoma coerulescens. Categorizamos cada caso con base en similitudes sociales y comparamos la reproduccion entre grupos familiarcs monogamos, y machos y hembras poliginos. No encontramos diferencias en la tasa relativa dc poliginia entre las 3 poblaciones. Ninguna de estas tres condiciones: presencia de ayudantes, proportion anual dc los sexos de los ayudantes o sobrevivencia de hembras reproductivas. esruvo asociada con dichos eventos de poliginia. El resultado de la reproduction fire similar entre machos poliginos y monogamos. aunque significativamcnte menor para hembras poliginas versus monogamas. La poliginia en estas urracas parece ocurrir bajo ciertos contcxtos sociales pero es raro aiin euando esos contcxtos no lo son. Ninguno de los sexos parece beneficiarse de apareamientos poliginos si bien la formation de triadas poliginas podria ser mejor que evitar reproducirse. Palabras clave: conflicto sexual, monogamia, poliginia, reproduccion cooperativa, sistemas de apareo., Monogamy is hypothesized to occur when conditions favoring polygamy or other mating systems arc absent or costly (Wittenberger and Tilson 1980, Klug 2018). Originally, birds were thought to be predominantly [...]

Introduction The title of this essay requires explanation. While most readers will have some idea of what human wisdom consists in, it is less common to speak of animal and, [...]

The Eastern Black Rail (Laterallus jamaicensis jamaicensis) is listed as Threatened under the United States Endangered Species Act and as Endangered in 6 states along the Atlantic Coast. Black Rails are difficult to observe and documentation of definitive breeding evidence is limited. This, along with perceived overlaps between the breeding and migratory periods, has led to uncertainty about the breeding status of calling birds across a large portion of their range. To delineate breeding and migratory periods, I examined the phenology of breeding records (N = 170) and documented 'presumed migrants' (N = 55) based on rails that hit radio towers, lighthouses, and buildings or were found in inner cities, on ships-at-sea, or on offshore islands. Nesting in Eastern Black Rails extends 3 months from mid-May to mid-August and peaks during the third week of June. Based on the available sample there is no evidence that egg dates vary with latitude along the Atlantic Coast. Presumed migrants were recorded from early March to early May and from early September to early November. Breeding observations and records of presumed spring migrants overlapped during the first 2 weeks of May. The overlap includes only 2.4% of breeding records. There was no overlap between records of presumed fall migrants and the breeding season. Received 26 June 2020. Accepted 22 February 2021. Key words: eastern North America, egg dates, fall migration. Great Plains. Midwest, nesting, spring migration. El rascon Laterallus jamaicensis jamaicensis se encuentra enlistado como Amenazado por el Endangered Species Act de los Estados Unidos y como En peligro en 6 estados a lo largo de la costa Atlantica. Estos rascones son dificiles de observar y la documentacion de evidencia definitiva de reproduccion es limitada. Esto, junto con los traslapes que se perciben entre sus periodos de anidacion y migracion, nos ha traido incertidumbre sobre el estatus de las aves que emiten llamados en buena parte de su rango. Para delinear sus periodos de anidacion y migracion, examine la fenologia de los registros de anidacion (N-170) y documente individuos 'presumiblemente migratorios' (N = 55) con base en rascones que tuvieron colisiones con torres de radio. faros y edificios, o que fueron en ciudades interiores. barcos en el mar o en islas lejos de la costa. La anidacion de Laterallus jamaicensis se extiende por 3 meses. de mediados de mayo a mediados de agosto, y tiene su pico en la tercera semana de junio. Con base en la muestra disponible. no hay evidencia de que las fechas de los huevos varian con la latitud en la costa Atlantica. Los presuiniblcmcnte migratorios se registraron de principios de marzo a principios de mayo y de principios de septiembre a principios de noviembre. Las observaciones de reproduccion y los registros de presumiblemente migratorios en primavera se traslapan durante las primeras 2 scmanas dc mayo. Este traslape incluye unicamente 2.4% de los registros de reproduccion. No hay traslape entre registros de presumiblemente migratorios en otoho y la temporada reproductiva. Recibido el 26 de junio de 2020. Aceptado el 22 de febrero dc 2021. Palabras clave: anidacion, este de Norteamerica. fechas de huevos. Grandes Planicies. Medio Oeste. migracion de otono. migracion de primavera., The Black Rail (Laterallus jamaicensis) breeds in tidal and freshwater marshes within disjunct ranges throughout the Americas. Currently, 2 recognized subspecies breed in North America (California Black Rail [L. j. [...]

Agricultural management, particularly haying, can cause synchronous nest failure of ground-nesting songbirds. As a consequence, these birds may subsequently renest and choose a new social mate (divorce). This study (1) quantified within-year and between-year divorce rates of grassland songbirds, and (2) determined if divorce rates differed after haying or predation-caused nest failure, and if so, whether divorce influenced reproductive success. From 2002 to 2017, we monitored 121 Bobolink (Dolichonyx oryzivorus) pairs and 436 Savannah Sparrow (Passerculus sandwichensis) pairs in an agricultural region of Vermont, USA. Within-year and between-year divorce rates were 0-84.9% for Bobolinks and 17-69.1 % for Savannah Sparrows. Between years, Bobolinks, but not Savannah Sparrows, were more likely to divorce after nest failure, but haying did not influence divorce rates. Within years, Savannah Sparrows were more likely to divorce after nest failure, but as with Bobolinks, divorce rates in Savannah Sparrows were not different between nests that failed due to haying or predation. Across all Savannah Sparrow renests, divorce had no influence on the number of young fledged per female. However, between years, female Bobolinks that divorced fledged more young in their first attempt while those that did not divorce fledged more young in their second attempt. This study showed that pairing decisions were not differentially affected by cause of nest failure. Further, we identified no reproductive benefit to divorce. Our results indicate no adaptive benefit and potentially a significant reproductive cost to divorce, and that these effects vary between species. Received 22 January 2019. Accepted 20 October 2020. Key words: agricultural management, Bobolink, grassland songbird, haying, mate choice. Savannah Sparrow. El manejo agricola, particularmente el cultivo de forrajes, puede causar perdidas sincronicas en pajaros que anidan en el suelo. Como consecuencia, estas aves pucden reanidar subsecuentementc y elegir una nueva pareja social (divorcio). Este estudio 1) cuantifico las tasas de divorcio intra- e interanuales de pajaros de pastizales y 2) determino si las tasas de divorcio difirieron despues de la siega de forrajes o fallos en el nido ocasionados por depredadores, y de ser asi, discernir si el divorcio influyo en el exito reproductivo. De 2002-2017 monitoreamos 121 parejas del arrocero Dolichonyx oryzivorus y 436 parejas del gorrion Passerculus sandwichensis en una region agricola de Vermont. Estados Unidos. Las tasas de divorcio intra- e interanuales fueron 0-84.9% para el arrocero y 17-69.1 % para el gorrion, respectivamente. Entre anos, los arroccros, mas no los gorriones, fueron mas proclives a divorciarse despues del fallo del nido. si bien la siega no influyo en la tasa dc divorcios. Intraanualmente, los gorriones fueron mas proclives a divorciarse despues del fallo del nido, si bien como en el caso de los arroceros sus tasas de divorcio no dificren entre nidos fallidos por la siega o la depredacion. Entre todas las reanidaciones del gorrion, el divorcio no tuvo influencia en el numero de polluclos emancipados por hembra. Sin embargo, de manera intcranual las hembras de arrocero que se divorciaron emanciparon mas polluelos en su primer intento mientras que aquellas que no se divorciaron emanciparon mas polluelos en su segundo intento. Este estudio muestra que las decisiones para fopnar parejas no fueron diferencialmente afectadas segun las causas que ocasionaron el fallo de los nidos. Mas aun, no identificamos ningun beneficio reproductivo del divorcio. Nuestros resultados indican que no hay un beneficio adaptativo o un costo potencialmente significativo por divorciarse y que sus efectos varian entre especies. Palabras clave: Dolichonyx oryzivorus, eleccion de pareja. manejo agricola, manejo cultural, pajaros dc pastizal, Passerculus sandwichensis, siega., The decision to divorce--select a different social mate in a subsequent nest attempt while the original mate is available to pair with--may significantly influence lifetime fitness (Culina et al. 2015, [...]

Territorial protandry, or early season male-biased settlement at breeding sites, is a widespread phenomenon in a range of animal breeding systems. While protandry is common across several avian lineages and has been linked with increased reproductive success of earlier breeding males in terrestrial species, the selective advantage of breeding protandry has only rarely been studied in seabirds. We assessed the seasonal changes in the sex ratio at the breeding site and sex-specific correlates of arrival date with reproductive success during 2 breeding seasons of a colonial seabird, the Australasian Gannet (Morus serrator), at Cape Kidnappers, New Zealand. We found no biases in overall sex ratios of adults and fledglings but detected a male sex bias during nest site establishment, and a significantly higher probability of reproductive success for earlier-settling males. In contrast, the reproductive success of females did not correlate with the timing of arrival. Our findings provide an assessment of the sex differences in reproductive correlates of the timing of breeding settlement in gannets and are consistent with selective advantages as suggested by indirect selection hypotheses. This study contributes to our understanding of the fitness benefits of protandry, and its linkages with sex differences in breeding philopatry and mate fidelity, in a long-lived seabird species with obligate and extended biparental care. Received 6 September 2017. Accepted 16 December 2019. Key words: Australasian Gannet, behavioral dimorphism, breeding ecology, Morus senator, reproductive benefits, territorial protandry La protandría territorial, o establecimiento estacional temprano sesgado a machos en sitios de reproducción, es un fenómeno generalizado en muchos sistemas reproductivos en animales. Si bien la protandría es común en varios linajes de aves y ésta ha sido vinculada con incrementos en el éxito reproductivo de los machos que anidan temprano en especies terrestres, la ventaja selectiva de la protandría reproductiva ha sido estudiada raramente en aves marinas. Durante 2 temporadas reproductivas, determinamos los cambios estacionales en la proporción de sexos en el sitio de reproducción y correlaciones especificas a sexo entre fecha de arribo y éxito reproductivo de un ave marina colonia!, el alcatraz Monis serrator, en Cape Kidnappers, Nueva Zelandia. No encontramos sesgos en las proporciones de sexos de adultos y polluelos, aunque detectamos un sesgo de sexo hacia machos durante el establecimiento de nidos y una probabilidad significativamente más alta de éxito reproductivo de los machos que se establecen temprano. En contraste, el éxito reproductivo de las hembras no se correlaciona con la temporalidad de su llegada. Nuestros hallazgos proveen una determinación de las diferencias entre sexos en las correlaciones reproductivas de la temporalidad de establecimiento reproductivo y son consistentes con sus ventajas selectivas como sugiere la hipótesis de la selección indirecta. Este estudio contribuye a nuestro entendimiento de los beneficios reproductivos de la protandría, y su relación con diferencias entre sexos en filopatria reproductiva y fidelidad a pareja en una especie longeva de ave marina con cuidado biparental obligado y extendido. Palabras clave: Alcatraz, beneficios reproductivos, dimorfismo conductual, ecología de la reproducción, Morus serrator, protandría territorial, Territorial protandry, or the tendency for males to arrive at breeding sites before females (Morbey and Ydenberg 2001), occurs in a diverse array of animals and may be a critical [...]