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1. CHANGES IN SPRING ARRIVAL DATES OF RUFOUS HUMMINGBIRDS (SELASPHORUS RUFUS) IN WESTERN NORTH AMERICA IN THE PAST CENTURY

   Courter, Jason R. ( March 2017 , Wilson Ornithological Society Annual Meeting)

   Warming temperatures have been linked to advancing spring migration dates of birds, although most studies have been conducted at individual sites. Problems may arise if birds arrive or depart before or after associated food resources reach critical lifecycle stages. I compared mean first arrival dates of Rufous Hummingbird (Selaphorus rufus), a prolific pollinator and long-distance migrant, between 1895-1969 and 2006-2015 at eight locations in Oregon, Washington, and British Columbia. Historical arrivals were reported through the North American Bird Phenology Program and recent arrivals were estimated from temporal occupancy patterns using eBird checklists. Results indicated that hummingbirds arrived 8 and 11more »days later in the recent time period in two coastal cities in Oregon and 7-17 days earlier in northern, more inland cities in Washington and British Columbia. Spring temperatures have increased in the past century in much of this region and birds arrived earlier in years with warmer spring temperatures, suggesting that migratory advancements were climate-related. Later arrivals reported in coastal regions of Oregon in the recent time period may suggest that Rufous Hummingbirds are bypassing coastal areas to take advantage of more predictable conditions along inland migratory routes, or are shifting their breeding ranges northward, notions both supported by declining population trends observed in Breeding Bird Survey data. My results provide justification for the investigation of the ecological impacts of climate change on birds in coastal vs. inland environments and a framework for comparing information from two extensive and emerging datasets to better understand the impacts of climate change on bird migration.« less
2. Birds advancing lay dates with warming springs face greater risk of chick mortality

   https://doi.org/10.1073/pnas.2009864117  

   Shipley, J. Ryan ; Twining, Cornelia W. ; Taff, Conor C. ; Vitousek, Maren N. ; Flack, Andrea ; Winkler, David W. ( September 2020 , Proceedings of the National Academy of Sciences)

   In response to a warming planet with earlier springs, migratory animals are adjusting the timing of essential life stages. Although these adjustments may be essential for keeping pace with resource phenology, they may prove insufficient, as evidenced by population declines in many species. However, even when species can match the tempo of climate change, other consequences may emerge when exposed to novel conditions earlier in the year. Here, using three long-term datasets on bird reproduction, daily insect availability, and weather, we investigated the complex mechanisms affecting reproductive success in an aerial insectivore, the tree swallow (Tachycineta bicolor). By examining breedingmore »records over nearly half a century, we discovered that tree swallows have continuously advanced their egg laying by ∼3 d per decade. However, earlier-hatching offspring are now exposed to inclement weather events twice as often as they were in the 1970s. Our long-term daily insect biomass dataset shows no long-term trends over 25 y but precipitous drops in flying insect numbers on days with low ambient temperatures. Insect availability has a considerable impact on chick survival: Even a single inclement weather event can reduce offspring survival by >50%. Our results highlight the multifaceted threats that climate change poses on migrating species. The decoupling between cold snap occurrence and generally warming spring temperatures can affect reproductive success and threaten long-term persistence of populations. Understanding the exact mechanisms that endanger aerial insectivores is especially timely because this guild is experiencing the steepest and most widespread declines across North America and Europe.

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3. Behavioral responses to spring snow conditions contribute to long-term shift in migration phenology in American robins

   https://doi.org/10.1088/1748-9326/ab71a0  

   Oliver, Ruth Y. ; Mahoney, Peter J. ; Gurarie, Eliezer ; Krikun, Nicole ; Weeks, Brian C. ; Hebblewhite, Mark ; Liston, Glen ; Boelman, Natalie ( April 2020 , Environmental Research Letters)

   Migratory birds have the capacity to shift their migration phenology in response to climatic change. Yet the mechanistic underpinning of changes in migratory timing remain poorly understood. We employed newly developed global positioning system (GPS) tracking devices and long-term dataset of migration passage timing to investigate how behavioral responses to environmental conditions relate to phenological shifts in American robins (Turdus migratorius) during spring migration to Arctic-boreal breeding grounds. We found that over the past quarter-century (1994–2018), robins have migrated ca. 5 d/decade earlier. Based on GPS data collected for 55 robins over three springs (2016–2018), we found the arrivalmore »timing and likelihood of stopovers, and timing of arrival to breeding grounds, were strongly influenced by dynamics in snow conditions along migratory paths. These findings suggest plasticity in migratory behavior may be an important mechanism for how long-distance migrants adjust their breeding phenology to keep pace with advancement of spring on breeding grounds.

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4. Intra‐specific variation in migration phenology of American Kestrels ( Falco sparverius ) in response to spring temperatures

   https://doi.org/10.1111/ibi.12953  

   Powers, Breanna F. ; Winiarski, Jason M. ; Requena‐Mullor, Juan M. ; Heath, Julie A. ( March 2021 , Ibis)

   Abstract In migratory birds, among- and within-species heterogeneity in response to climate change may be attributed to differences in migration distance and environmental cues that affect timing of arrival at breeding grounds. We used eBird observations and a within-species comparative approach to examine whether migration distance (with latitude as a proxy) and weather predictors can explain spring arrival dates at the breeding site in a raptor species with a widespread distribution and diverse migration strategies, the American Kestrel Falco sparverius. We found an interactive effect between latitude and spring minimum temperatures on arrival dates, whereby at lower latitudes (short-distance migrants)more »American Kestrels arrived earlier in warmer springs and later in colder springs, but American Kestrels at higher latitudes (long-distance migrants) showed no association between arrival time and spring temperatures. Increased snow cover delayed arrival at all latitudes. Our results support the hypothesis that short-distance migrants are better able to respond to conditions on the breeding ground than are long-distance migrants, suggesting that long-distance migrants may be more vulnerable to shifts in spring conditions that could lead to phenological mismatch between peak resources and nesting.« less
5. Mapping Temperate Forest Phenology Using Tower, UAV, and Ground-Based Sensors

   https://doi.org/10.3390/drones4030056  

   Atkins, Jeff W. ; Stovall, Atticus E. ; Yang, Xi ( September 2020 , Drones)

   Phenology is a distinct marker of the impacts of climate change on ecosystems. Accordingly, monitoring the spatiotemporal patterns of vegetation phenology is important to understand the changing Earth system. A wide range of sensors have been used to monitor vegetation phenology, including digital cameras with different viewing geometries mounted on various types of platforms. Sensor perspective, view-angle, and resolution can potentially impact estimates of phenology. We compared three different methods of remotely sensing vegetation phenology—an unoccupied aerial vehicle (UAV)-based, downward-facing RGB camera, a below-canopy, upward-facing hemispherical camera with blue (B), green (G), and near-infrared (NIR) bands, and a tower-based RGBmore »PhenoCam, positioned at an oblique angle to the canopy—to estimate spring phenological transition towards canopy closure in a mixed-species temperate forest in central Virginia, USA. Our study had two objectives: (1) to compare the above- and below-canopy inference of canopy greenness (using green chromatic coordinate and normalized difference vegetation index) and canopy structural attributes (leaf area and gap fraction) by matching below-canopy hemispherical photos with high spatial resolution (0.03 m) UAV imagery, to find the appropriate spatial coverage and resolution for comparison; (2) to compare how UAV, ground-based, and tower-based imagery performed in estimating the timing of the spring phenological transition. We found that a spatial buffer of 20 m radius for UAV imagery is most closely comparable to below-canopy imagery in this system. Sensors and platforms agree within +/− 5 days of when canopy greenness stabilizes from the spring phenophase into the growing season. We show that pairing UAV imagery with tower-based observation platforms and plot-based observations for phenological studies (e.g., long-term monitoring, existing research networks, and permanent plots) has the potential to scale plot-based forest structural measures via UAV imagery, constrain uncertainty estimates around phenophases, and more robustly assess site heterogeneity.« less