Nebraskaland

52 Nebraskaland • November 2025 MIXED BAG USING DAYLIGHT TO UNDERSTAND BIRD MOVEMENTS By Stephen J. Brenner, Audubon Great Plains, and Joel Jorgensen, Nongame Bird Program Manager Modern technology has unlocked a kaleidoscope of tools that can be used to reveal animal movements, including those of small migratory birds. Transmitters that use the same GPS that we tap into to navigate our vehicles to restaurants, airports and auto-part stores can also be harnessed to follow the real-time movements of many animals. However, most migratory songbirds that breed in our state present a challenge for GPS technology. As many migratory species need to travel over 1,000 miles twice a year and weigh as little as a couple dozen paper clips, most are incapable of carrying the heavy load of a GPS unit while in fl ight. But there is a less weighty alternative that utilizes an old school technology to answer new questions about the annual movements of migratory birds. Light-level geolocators are small data loggers whose only function is to record the length of daylight every 24-hour period. As all the information is stored on board and there is no need to transmit or spend energy fi nding a satellite, almost no battery is required and the simplicity of the technology greatly reduces the weight. Yet with this simple data of sunrise and sunset times paired with knowing the date and original location of deployment, these tiny devices can be used to track the movements of small songbirds traveling long distances anywhere across the globe. The positional data from geolocators compared to GPS units is certainly less precise: think about a 100-kilometer scale for a geolocator and a 10-meter scale for GPS. But with the newest light-level geolocators coming in at under 0.5 grams (that's roughly 1/6th the weight of a penny), there is no better way to safely track the incredible journeys of these amazing animal athletes on their endurance fl ights across the continent. One such small but impressive long-distance traveler is the ovenbird. Ovenbirds are migratory wood-warblers that spend much of their time foraging on the ground feeding on invertebrates and blasting their loud, escalating "teacher- Teacher-TEACHER!" song. The ovenbird got its swanky name because their nest has a domed appearance that some might say resembles an oven. This species has a large breeding range across North America but a limited breeding range in Nebraska, restricted primarily to the Pine Ridge, Niobrara River Valley and sparingly along the Missouri River Valley. Its wintering range is also large, spanning from northern South America up through parts of northern Mexico and much of the Caribbean. Birds from the core range of this species have been tracked before using geolocators, tracking migrations from the expansive boreal forests of Canada down to Central America, and from the islands of the Caribbean to the idyllic woods of New England. However, no one has studied the populations at the very edge of their range in western Nebraska, and as you might expect, no one is sure where these individuals migrate, spend the winter, or what their survival rate is compared to more well-studied counterparts in eastern North America. Researchers at Nebraska Game and Parks and Audubon Great Plains set out to understand where warblers living on the edge in the Cornhusker state might spend the winter months, and what — if any — breeding success these birds have relative to previously- studied populations. As it so happens, ovenbirds breeding at the range-limits in Nebraska overwinter at the known nonbreeding range-limits in northwestern Mexico and Baja California, and it seems very likely from the data that Nebraska ovenbirds may have extended the map of where this species spends the "off -season" in western Mexico. As if new tropical wintering grounds some 1,300 miles away weren't interesting enough, three years of data have revealed that ovenbirds breeding in the pine forests of the western Plains have very high survival rates relative to birds breeding in both sub-optimal and high-quality habitats out east. This research completes the larger picture about the breeding and migratory ecology of this incredible bird across its range, and is a testament to the amazing journeys and geographic connections that even the smallest birds in our state can make. Ovenbirds have a limited breeding range in Nebraska. JON FARRAR, NEBRASKALAND

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