L.A.R.C. Research in Detail
Overview
The Lackawanna Avian Research Center (L.A.R.C.) studies how migrating songbirds and Northern Saw-whet Owls are affected by the habitats they stop in, the weather they have passed through, and the air they breathe. Our work rests on 23 years of capturing, measuring, and releasing birds at field sites in northeastern Pennsylvania. Because we use the same methods year after year, we can compare birds across seasons, species, and decades.
Four questions drive our research:
1. Do non-native shrublands help migrating birds refuel?
2. How do a bird's age, sex, and earlier journey shape how it fares?
3. Does air pollution affect migrating birds?
4. How are birds, and the owls that prey on small mammals, responding to climate and food supply?
Our findings on habitat and on earlier-journey effects have appeared in peer-reviewed scientific journals. The air-quality, body-size, and owl projects are ongoing.
Go here and here to see more details about our research, including student research projects.
Our Field Site and 23 Years of Monitoring
Our data come from field sites both near and within Lackawanna State Park in Dalton, Pennsylvania, where we have caught migrating birds in spring and fall for 23 years. Each bird is gently handled, banded with a small numbered leg band, measured, and released, usually within minutes. Banding lets us recognize individual birds if they are caught again.
For every bird, we record:
• Species, sex, and age, which show who is passing through
• Date and time of capture, which show when birds arrive and how their timing shifts from year to year
• Body mass, which tells us how much fuel a bird is carrying (explained below)
• Wing, tail, and leg (tarsus) length, which describe a bird's body size, so we can tell a large bird from a heavy one
• Feather wear and molt, which show a bird's condition and its stage in the annual cycle
• Feather mites and ticks, which give a rough measure of parasite load
A research project this long is rare. Single seasons can be misleading, since weather, food, and bird numbers vary from year to year. Many years together let us separate real patterns from chance.
Why We Weigh Birds: Mass Is a Measure of Fuel
Body mass is our main measure of how well a bird is refueling, because fat is the fuel for migration. Fat stores more energy per gram than anything else a bird can carry, so before and during migration birds put on fat the way a driver fills a gas tank. Many songbirds fly in long, exhausting bursts and then stop for days to rebuild their reserves before the next leg.
Getting an accurate measure of fat in a live bird is difficult. It requires expensive instruments that are rarely practical in the field, especially when many birds must be handled quickly and gently. Weighing a bird is simple, fast, and inexpensive, and it minimizes stress on the bird. For these reasons, we and other researchers commonly use body mass as an indicator of fat gain or loss.
A small songbird weighs only a few grams, and much of the weight it gains or loses during a stopover is fat. A bird that is heavier later in its stay has probably been building fuel. A bird that is losing weight, or unable to gain, is probably burning more energy than it can replace. Because body size also affects weight, we measure wing, tail, and leg length as well, so that large birds are not mistaken for fat ones.
This makes mass a useful report card for habitat. A high-quality stopover site lets birds gain mass, and therefore fat, at a high rate. A good site offers plenty of the right foods, so birds can refuel quickly, spend less time on the ground, and continue their journey in better condition. A poor site makes it hard to refuel, so birds stay longer, arrive at their next stop with less in reserve, and face greater risk.
A Non-Native Shrubland: Looks Good, but Does It Work?
In several published studies, we found that migratory birds using our shrubland have a reduced ability to gain mass, and sometimes no ability to gain mass at all. Our site is dominated by non-native bush honeysuckles and European buckthorn, two shrubs brought here from other parts of the world. They now thrive in old fields and along forest edges across the Northeast, so what we learn here applies to many of the places migrants stop.
These thickets look like good habitat. They offer dense cover and heavy crops of berries. But for a bird that may still have hundreds of miles to fly, arriving at the next stop with fewer reserves can mean slower migration, greater risk, and lower odds of surviving and breeding successfully.
Scientists are still working out exactly why these shrubs fall short. Several things likely play a part:
• Berries. Honeysuckle and buckthorn fruit is eaten readily, but it is generally lower in the fats birds need than many native fruits, such as spicebush or dogwood. Buckthorn berries also have a laxative effect, so birds may pass them quickly and absorb less.
• Insects. Native plants usually host far more insects than non-native ones, because the insects evolved alongside them. A thicket of honeysuckle and buckthorn may support fewer of the caterpillars and other insects that songbirds rely on for protein.
Because we have weighed birds at the same site for more than two decades, we can follow these patterns over time and across species, not just in a single season.
Who the Bird Is and Where It Has Been
How well a bird refuels at our site depends on both the bird itself and the journey it has already made. Several of our publications examine two kinds of influence: those that come from within the bird, and those that come from the conditions it experienced earlier in the year.
Intrinsic factors: age and sex. Young birds on their first migration have never made the trip and may be less experienced at finding food. Males and females can also differ in when they migrate, how much they weigh, and how they use habitat. Our long-term records let us compare these groups and see which birds struggle the most.
Extrinsic factors: conditions earlier in the journey. A bird arriving at our site has already traveled a long way. It may have spent the winter in the tropics and crossed several states or regions before reaching us. Scientists call the lasting effects of those earlier conditions carryover effects. Temperature and rainfall on the wintering grounds, or at places passed during migration before arrival, can influence a bird's condition when it arrives and how well it recovers once it stops.
This means a bird's success at our site cannot be understood in isolation. By combining decades of captures with weather data from earlier in each bird's journey, we can trace how conditions across the whole migration, not just what happens here, shape the outcome.
Air Quality and Migrating Birds
We are testing whether air pollution affects how much migrating birds weigh and how active they are, and early results suggest the answer depends on the species. Air quality is well studied in people but rarely in wild birds, especially during the effort of migration. Because mass reflects fuel, a bird that weighs less on dirtier days may be less prepared for the journey ahead.
We match each bird's capture date to satellite-based estimates of daily air pollution for rural Pennsylvania: sulfur dioxide (SO2), nitrogen dioxide (NO2), and fine particles (PM2.5). Our models also account for factors such as the day of the season, the year, and the time of day, since birds weigh different amounts at different times.
Two preliminary patterns stand out:
• Sulfur dioxide. In an analysis of 20 species, seven weighed less at higher SO2 levels, one (the red-eyed vireo) weighed more, and the rest showed no clear relationship. We are investigating whether differences in how species feed, such as insect eaters versus fruit eaters, explain the opposite directions.
• Fine particles. Traill's flycatchers were captured less often and weighed less when PM2.5 was high, suggesting they were less active and in poorer condition.
These results are still being analyzed and should be read as early findings, not conclusions. Satellite estimates are also averages over a broad area. To measure what birds actually breathe at our site, we are building a solar-powered air-quality monitor that will record ozone, SO2, nitrogen oxides, PM2.5, and volatile organic compounds on the ground, where the birds are.
Climate Change, Migration Timing, and Body Size
Because our monitoring spans more than two decades with consistent methods, it lets us examine how a changing climate is affecting when birds migrate and how large they are. Few places have records long enough to show gradual change, and short studies cannot separate a real trend from a few unusual years.
Migration timing. Every bird we catch has a recorded date and time, so we can see whether species are passing through earlier or later than they used to, and whether timing follows temperature and other conditions from year to year. Timing matters because birds that arrive out of step with the insects and fruit they depend on may find less food when they need it most.
Body size. Some studies elsewhere suggest that bird populations may be changing in body size as climates warm. Our measurements of wing, tail, and leg length, taken on the same standard protocol over many years, allow us to test whether the birds at our site are changing in size.
We are asking whether the bodies of these birds have changed in size over two decades, because body size is one way wildlife can respond to a changing environment. To answer this, we compare birds caught during spring and fall migration with young birds hatched locally, which we can identify by their juvenile plumage when they are caught in August. Including locally hatched birds lets us look at size change in birds that grew up at our site, as well as in birds passing through.
This project is under way. We have analyzed data through 2025 and will add 2026 once this year's captures are complete.
Northern Saw-whet Owls
In autumn we also study the Northern Saw-whet Owl, a tiny, secretive owl that migrates through our area at night and is rarely seen unless it is caught. We have two owl projects under way.
Voles, climate, and breeding. We are investigating whether the owls' breeding success is tied to the food they eat on their northern breeding grounds. Saw-whets that nest in Ontario and Quebec feed heavily on small rodents, especially red-backed voles and deer mice, whose numbers rise and fall in cycles. Those cycles may depend on acorn crops (oak mast), snow cover, temperature, and rainfall. We are also testing whether satellite measures of how green the vegetation is during the breeding season can stand in for the food supply available to voles. With about 10 years of fall owl captures, we plan to use a statistical approach that scans different time windows to find which weather and vegetation conditions best predict vole abundance or owl breeding success.
Eye color. Saw-whet iris color varies noticeably from owl to owl, and we want to know why. During banding we photograph each owl's eye with a Nikon D5600 camera and flash, saving both a standard JPEG and an unprocessed raw file. A standard color reference chart lets us calibrate the colors, and we measure iris color with image-analysis software (Fiji/ImageJ). We then plan to explore whether iris color differs by sex and age, and whether it is associated with blood parasite load, feather coloration, or migration timing.
Why It Matters
Habitat that looks healthy to us may not meet the needs of migrating birds, and long-term data can show the difference. Birds are early warning systems: when their weight, numbers, or health change, something in their environment has usually changed too.
Our results bear on several real decisions:
• Habitat management. Land managers must choose whether to remove invasive shrubs, replace them with native plants, or leave them in place. Our finding that honeysuckle and buckthorn limit mass gain suggests that restoring native vegetation could help more birds complete their journeys.
• Which birds are most at risk. Knowing that age, sex, and earlier-journey conditions shape how birds fare helps identify the birds, and the years, that are most vulnerable.
• Environmental health. Understanding how air pollution and climate affect birds helps us see how conditions that matter to wildlife also matter to people in the same places.
About L.A.R.C. and How to Help
L.A.R.C. is a small, community-powered nonprofit that combines scientific research with public education about migrating songbirds and Northern Saw-whet Owls. Our mission is to share this research with the public, including students, families, and neighbors, so that more people understand and care about the birds that pass through our region.
Support from the community helps us keep banding, build our air-quality monitor, and share this work. To learn more, donate, or find out about upcoming events, visit