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.

Declines among species of insect pollinators, especially butterflies, has garnered attention from scientists and managers. Often these declines have spurred governments to declare some species as threatened or endangered. We used existing presence–absence data from surveys for the threatened Dakota skipper Hesperia dacotae (Skinner) to build statistical maps of species presence that could be used to inform future monitoring designs. We developed a hierarchical Bayesian modeling approach to estimate the spatial distribution and temporal trend in Dakota skipper probability of presence. Our model included a spatial random effect and fixed effects for the proportion of two grassland habitat types: those on well-drained soils and those on poorly drained soils; as well as the topographic slope. The results from this model were then used to assess sampling strategies with two different monitoring objectives: locating new Dakota skipper colonies or monitoring the proportion of historically (pre-2000) extant colonies. Our modeling results suggested that the distribution of Dakota skippers followed the distribution of remnant grasslands and that probabilities of presence tended to be higher in topographically diverse grasslands with well-drained soils. Our analysis also showed that the probability of presence declined throughout the northern Great Plains range. Our simulations of the different sampling designs suggested that new detections were expected when sampling where Dakota skippers likely occurred historically, but this may lead to a tradeoff with monitoring existing sites. Prior information about the extant sites may help to ameliorate this tradeoff.

Conservationists and scientists throughout the world consider butterflies important indicators of broadscale factors affecting global biodiversity. And like other facets of biodiversity, declines in many butterfly populations appear related to human activities, and the potential of their extinction could jeopardize key ecosystem services. The regal fritillary (Argynnis idalia), a butterfly associated with tall-and mixed-grass prairies in the United States, is a species currently being considered for federal protection under the Endangered Species Act. As with many butterflies, a paucity of data makes evidence-based assessments of their population and distributional status difficult. Citizen science data provide one possible source of broadscale information about this species, but using these data is not simple because of spatial scaling and sampling bias problems. Here, we developed a model to analyze a data set from the citizen science program called the Fourth of July Butterfly Count (4JC) to make inferences about regal fritillary abundance in the Great Plains and Midwest regions of the United States. More specifically, we aimed to determine the extent to which grassland fragmentation, spring weather conditions, or other spatial factors were correlated with the intensity of use within 4JC survey areas. Our findings indicated that regal fritillaries used locations surrounded by grassland and with minimal forest cover. We included smoothing spline terms in our model, which indicated other sources of spatial structuring in these data. It is possible that these additional sources of variation could reflect variation in habitat quality. We also found that local averaged spring weather variables indicated that regal fritillary abundance varied over a wider range of precipitation conditions, but a narrower range of temperature conditions. Further analyses indicated that a systematic increase in temperature from climate change could lead to a pronounced northward shift in the regal fritillary's distribution. These findings have implications for the development of a recovery plan, since such a plan will need to outline a strategy that Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Table S1. Summary of model selection results for the presence of the dawn song bout of 1 paired male Cerulean Warblers in south-central Indiana, USA in 2017 as a function of 2 seasonality, breeding stage, and weather. Models are ranked by ascending value of 3 Akaike's Information Criterion corrected for small sample sizes (AICc); wi is the model 4 weight, and df is the number of parameters. All models also included a random effect 5 ("individual"). Models with ΔAICc values of < 2.0 were considered equally plausible. 6 7 Model ΔAICc df wi Julian date 0.0 0.2655 Julian date + temperature 0.9 0.1658 Julian date + wind 1.2 0.1458 Julian date + rain 2.0 0.0970 Julian date + temperature + wind 3.0 0.0589 Julian date + temperature + rain 3.1 0.0550 Julian date + wind + rain 3.4 0.0482 Julian date + breeding stage 4.3 0.0306 Julian date + temperature + wind + rain 5.3 0.0190 Julian date + breeding stage + temperature 5.3 0.0184 Julian date + breeding stage + wind 5.5 0.0166 Julian date + breeding stage + rain 6.4 0.0109 Null model 6.5 0.0102 Julian date + breeding stage + temperature + wind 7.5 0.0063 Julian date + breeding stage + temperature + rain

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