Cerulean Warblers (Setophaga cerulea) are among the fastest declining Nearctic-Neotropical migrant wood-warblers (Parulidae) in North America. Despite ongoing conservation efforts, little is known about their non-breeding distribution. In June 2016-2018, we deployed geolocators (n = 30) on adult male Cerulean Warblers in Indiana, USA, to track annual movements of individuals. Recovered geolocators (n = 4) showed that Cerulean Warblers occurred broadly throughout northern South America. Autumn migration lasted 44-71 days (n = 4), whereas spring migration lasted 37-41 days (n = 3). The average migration distance was 5268 km. During autumn migration, Cerulean Warblers made 1-4 stopovers (i.e., ≥2 days; n = 4) and 1-2 stopovers during spring migration (n = 3). When crossing the Gulf of Mexico during autumn migration, two birds stopped over after crossing, but not beforehand. Two others navigated through the Caribbean rather than crossing the Gulf of Mexico. During spring migration, one individual stopped after crossing, one individual stopped before crossing, and one individual stopped before and after crossing the Gulf of Mexico. No birds migrated through the Caribbean Islands during spring migration. These results represent novel information describing annual movements of individual Cerulean Warblers and will inform conservation efforts for this declining species.
The effect of climate on the population dynamics of rainforest vertebrates is known only for a limited subset of species and study locations. To extend this knowledge, we carried out an 8‐year population study of a Viverrid (Malay civet Viverra tangalunga) in the Wallacea biogeographical region (Buton Island, Sulawesi). Civets were trapped annually from 2003 to 2010, during which there were four weak to moderate El Niño events and one moderate La Niña event. In Indonesia, El Niño events are associated with drier than normal conditions, while La Niña is associated with wetter conditions. The number of individuals captured was strongly correlated with the 12‐month summed Southern Oscillation Index (SOI) prior to trapping, with significantly fewer individuals caught in years with lower summed SOI (i.e. stronger El Niño conditions). Adult civet body mass was significantly higher in El Niño years; mean adult male and female body masses were 10.6% and 4.0% greater in El Niño years. There was support for a 1‐year time lagged effect of El Niño on the apparent survival (1 – probability of disappearing from the study site due to death or emigration) of male (but not female) civets, which was approximately 50% higher in the year following El Niño events. Using spatially explicit capture–mark–recapture models, we were unable to detect any significant change in civet density between years, which was estimated as 1.36 ± 0.14 (se) individuals km−2. We suggest that increased apparent survival of males observed in the year after El Niño events was brought about by reduced dispersal (possibly associated with a change in mating tactic) rather than reduced mortality.
Many studies have shown that nest predators affect their prey indirectly by inducing changes in the behaviour of the prey. Studies suggest that the type and degree of nest defence strategies depends heavily on species, along with nest type and location. One such strategy, nest vigilance, allows individuals to collect information and make informed decisions based on their surroundings. In this study, we simulated the intrusion of a common avian nest predator (blue jay, Cyanocitta cristata) into the territory of nesting cerulean warblers (Setophaga cerulea) and evaluated eight different behavioural variables to determine their response to the nest predator. Female cerulean warblers were more vigilant on their nest when exposed to a potential predator compared to a nest with lower threat of predation. Females exposed to a nest predator increased incubation bout by 109% and brooding bout by 60%. Our data also suggest that male cerulean warblers reduce their provisioning rate during the early nestling stage (−1 feeding/hour) and late nestling stage (−3 feedings/hour), although more data are needed. Modification of incubation bout length and nestling provisioning rate are common strategies employed by songbirds to reduce activity around the nest, by decreasing detection opportunities of visually-oriented nest predators. Currently, the only understanding we have on how cerulean warblers respond to a nest predator is based on observational data. The results of this study provide the first evidence that cerulean warblers are able to identify species that pose a threat to the safety of their nest, and that they modify their behaviour to reduce nest detection by predators. The results of this study provide a better understanding of a relatively unknown aspect of the breeding behaviour of this species. This study is also first to describe how an open-cup, canopy-nesting species responds to an increase in nest predation threat.
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