Tropical Phenology in Temperate Regions

Abstract

Abstract. The chronology of birds' breeding has traditionally been thought to depend strongly on latitude, although it can be rather uneven among populations in close proximity. I estimated the extent of the breeding season in a population of the Red-necked Nightjar (Caprimulgus ruficollis) over three years in southwestern Spain. Data from brood patch development and appearance of recently fledged young provided evidence for a breeding season unusually extended (110 days) for a long-distance migrant. Flexible timing in reproduction appeared to affect individual's departure in migration. Although most adult nightjars gradually left the study area beginning in mid August, some late breeders left the area about a month later than the earliest migrants. Decreasing competition for food and free nesting territories, together with a food supply and predation pressure constant through the season, resemble conditions in the tropics and enable the nightjars to breed over an extended period despite inhabiting a temperate region. The nightjars' phenology was further expanded by a protracted period (≥35 days) of parental care, which also led to later molt prior to autumn migration. However, birds partially compensated for time costs to adjust to the annual cycle by initiating a simultaneous shedding of flight feathers immediately after hatching. In accordance with current studies showing how breeding events carry over into the annual routines of birds, results from this nightjar population come on top of recent hypotheses regarding new ways in which breeding, molt and migration could interact and condition each other. Resumen. La latitud es considerada habitualmente como un factor determinante de la cronología reproductiva de las aves, aunque ésta puede resultar dispar entre poblaciones cercanas. Durante tres años, estimé la duración del período reproductor en una población de Caprimulgus ruficollis del suroeste de España. Los datos sobre el desarrollo de la placa incubatriz y la aparición de pollos recién volados mostraron la existencia de un periodo reproductor inusualmente prolongado (110 días) para un migrador de larga distancia. La flexibilidad temporal en la reproducción aparentemente afectó a la partida migratoria de los individuos. Aunque la mayoría de los chotacabras abandonaron el área de estudio de forma gradual desde mediados de agosto, algunos reproductores tardíos partieron con una diferencia de un mes respecto a los primeros. La disminución en la competencia por el alimento y los territorios de cría, junto con el constante aporte de alimento y presión de depredadores, parecen emular condiciones típicamente tropicales, permitiendo a los chotacabras criar durante un largo periodo de tiempo a pesar de habitar regiones templadas. La fenología de los chotacabras se vio además extendida por un cuidado parental prolongado (≥35 días), lo que también generó retrasos en la muda previa a la migración otoñal. Sin embargo, las aves compensaron parcialmente estos costes temporales para ajustarse al ciclo anual, iniciando un...

Phylogeny, Historical Biogeography and the Evolution of Migration in Accipitrid Birds of Prey (Aves: Accipitriformes)

“…Alternatively, other factors, such as selection for early breeding or extended breeding season could generate differences in migratoriness between populations or species (e.g. Tökölyi & Barta 2011, Camacho 2013. Further work is required to clarify ecological determinants of migration in birds of prey.…”

Correlates of individual variation in the porphyrin-based fluorescence of red-necked nightjars (Caprimulgus ruficollis)

“…Most often, the UV-induced fluorescence of nestling plumage has been interpreted as a form of signaling genetic and phenotypic quality to parents 13,33 . Nonetheless, all juvenile nightjars measured in this study exceeded the age at which parents typically cease provisioning (35 days 34 ), indicating that porphyrins, insofar as they can be perceived under natural light, might still act as a signal later in life. For instance, the expression of porphyrin-based coloration so early in life might aid in reproductive signaling in the year post-hatching.…”

“…First, it is possible that porphyrin degradation is most pronounced at the beginning of the season, just around the summer solstice. Because of the protracted breeding period of nightjars (June-September 34 ), the daily exposure time of chicks to sunlight decreases by 20% throughout the season, potentially resulting in greater levels of fluorescence in late-fledging chicks. Second, in the case of adults, increased exposure to sunlight might have contributed to the slight decrease in fluorescence expression observed before the summer solstice, but the onset of molt likely provides a more straightforward explanation for the increasing trend recorded from then onwards.…”

“…Second, in the case of adults, increased exposure to sunlight might have contributed to the slight decrease in fluorescence expression observed before the summer solstice, but the onset of molt likely provides a more straightforward explanation for the increasing trend recorded from then onwards. Nightjars start molting during the chick-rearing period 34 and, therefore, the proportion of newly grown feathers fully loaded with intact porphyrins increases gradually until molt is completed before migration departure. Last, the selective mortality of individuals showing smaller pink patches could also result in the apparent increase in fluorescence as the summer progresses, although the relatively high juvenile and adult survival rates recorded in this population argue against this possibility 36,39 .…”

“…Fieldwork was conducted between 17 May and 16 September 2016 in an intensively (2008–2019) studied population of migratory red-necked nightjars in Doñana Natural Park, SW Spain (37°7′N, 6°33′W) 34,42 . Most nightjars arrive in the region in May, lay one or two clutches of 1–2 eggs between May and August, and head back to West Africa between September and October 34 . Males arrive from migration approximately one week before females, choose a territory, and vocalize to attract females.…”