Like many people, fall is my favorite season. The weather is often pleasant, the late-season wildflowers are in full bloom and teeming with bees and butterflies, and there is a noticeable change in the air after the late summer doldrums. Fall in the mid-Atlantic is especially enjoyable if you are a naturalist, for two reasons. First, you get to witness the subtle beauty of wildflowers and tree leaves changing color, and second, you start noticing differences in the local wildlife as many animals either become inactive or migrate south. Birds are the most famous and visible migrants, with about half of our North American songbirds flying to Central or South America in search of insects, which are scarce during our cold and snowy winters. However, several other animals migrate, including some bats and insects, like the green darner dragonfly and the monarch butterfly.
Monarchs
The monarch butterfly (Danaus plexippus) is instantly recognizable to both adults and children because of its large size and striking orange and black wings. Like many of our native butterflies and moths, their lives are entwined with native plants. Although monarch butterflies feed on the nectar of many flowers, they only lay their eggs on milkweeds (Asclepias sp.), a group of plants with colorful flowers that are named for their milky white latex. Once the caterpillars hatch, they start munching on the leaves during which they ingest toxic leaf compounds which make them distasteful to most predators. No milkweed means no monarch eggs or caterpillars! It is also Its survival is tightly linked to milkweeds (Asclepias sp.), a group of plants with colorful flowers that are named for their milky white latex. Although monarch butterflies feed on the nectar of many flowers, they only lay their eggs on milkweeds. Once the caterpillars hatch, they start munching on the leaves during which they ingest toxic leaf compounds which make them distasteful to most predators.
Unfortunately, monarchs are in decline, and the migratory subspecies that occurs in North America is categorized as ‘Vulnerable’ (the level above ‘Endangered’). We help conserve monarchs at each of our four sites by extensively planting multiple species of milkweeds and also by rearing caterpillars in captivity at our headquarters of Ashland Nature Center in Hockessin. Our friendly front desk crew of Glynne Nagle and Leah Awitan have been collecting caterpillars from around Ashland and rearing them on fresh common milkweed in large cages in our lobby. Hundreds of summer camp kids as well as visiting adults and families have enjoyed seeing our monarch display and getting close views of the caterpillars, pupa and emerging adults. So far, Glynne and Leah have released 41 monarchs!
Monarch migration
Monarchs are unusual among butterflies in that they undertake a long-distance migration. Although it was well-known that these half-gram insects flew south for the winter, nobody knew where they went. The mystery was solved in the 1970s when intrepid entomologists exploring the mountains of Mexico were stunned to stumble across trees dripping with monarchs!
A half century later, we now have a much better understanding of the routes and destinations of migrating monarchs because of a tagging program started by Dr Fred Urquhart of the University of Toronto and now organized by Monarch Watch. Volunteers throughout North America place a small sticker with a unique code on the wing of captive-reared monarchs or wild monarchs carefully captured in butterfly nets during the late-summer migratory period. Scientists can then track this butterfly’s journey if the code is reported by anyone who later recaptures the butterfly or finds it dead. Since just 2017, almost 7, 500 tagged monarchs have been either recaptured or found dead in North America, giving useful data on their migration routes and survival. Furthermore, a staggering 21, 000 tagged monarchs have been encountered in their overwintering areas in central Mexico! Monarch tagging is a great example of a community science project where thousands of volunteers contribute their time, effort and money to achieve a larger scientific goal.
If you would like to watch monarchs being tagged and released, please join us at our annual Monarch Migration Celebration at the DuPont Environmental Education Center on the Wilmington riverfront on Saturday September 20th, 2025, from noon until 4pm. There is fun for all the family with live animal displays, music and performance, nature walks, crafts and beginner paddling in the marsh! The incredible migration of this small but charismatic insect connects Delaware with Mexico. It is 2,500 miles between Wilmington and Angangueo, one of their wintering strongholds. Angangueo holds a Festival de la Mariposa Monarca (Monarch Butterfly Festival) every February. It is truly remarkable that there is a celebration in Delaware followed by another in Mexico a few months later, all for the same butterfly. Maybe some of our tagged Delaware monarchs will show up at their celebration!
Monarchs face several threats on their summer and wintering grounds, as well as during their migration. The main threat is the loss of feeding and roosting habitat to development, and a lack of the milkweeds essential for their reproduction. Thankfully, there are many ways you can help monarchs in Delaware, the easiest of which is to plant milkweeds. There are several beautiful native species you could plant in your yard, parks or schools to create ‘monarch waystations’. Some of these are available at our Fall Native Plant Sales on Saturday, October 4th, from 9 am – 3 pm at Coverdale Farm Preserve in Greenville and 9am – noon at Abbott’s Mill Nature Center in Milford. Click here for the list of enticing plants available!
Tracking birds on the move too!
Migration connects both people and places because the same animal may be familiar to those living thousands of miles apart, even though they may call it by a different name. We are learning much more about the migration and survival of multiple species of birds because of Motus (the Latin word for ‘movement’), a community of researchers throughout North and South America that place radio-transmitters on animals so their movement can be tracked by receiving towers erected by themselves or other researchers. A Motus tower was installed in the marsh at the DuPont Environmental Education Center in October 2020 and in just 5 years has detected an amazing 432 animals of 51 species! So far in 2025 it has detected 36 birds of 9 species, including warblers, orioles, American Kestrels and thrushes, including 7 Wood Thrushes tagged during a range-wide study that we are participating in. Long-range migrants detected this year include an Ovenbird tagged in Jamaica, a Wood Thrush tagged in Costa Rica, and a rare Bicknell’s Thrush tagged in Quebec last summer. As you can see in this intriguing summary (screenshot posted below), many birds funnel through Wilmington on their way south or north. So those birds you see flying over Wilmington today may soon be enjoyed by people living in Mexico, along with our monarchs!
Listening for birds
An exciting addition to the biological monitoring we undertake at Ashland is a Bird Weather device received from a generous donor. This PUC (Portable Universe Codec) contains a microphone and uses artificial intelligence to identify birds by their songs and calls. Anyone can buy a PUC and put it out in their backyard to find out which birds are present while also contributing data on the distribution of different birds, since there are now over 2, 500 PUCs deployed in North America alone. They can easily be connected to a power outlet and wireless internet, so the recordings are stored in the cloud. However, they can also be deployed in remote areas using batteries as a power source and an SD card to store data. We have been using our PUC to ‘listen’ for both resident and migrating birds and have detected several uncommon migrants recently including Red-breasted Nuthatches and Rose-breasted Grosbeaks. To see the Ashland data for yourself, click on the ‘Explore’ tab in the top right corner of the home page, and drop down to ‘Data Explorer’. Type ‘Delaware Nature Society 1’ into the ‘Stations’ box on the left-hand side then select a Time Range (e.g. ‘Last 24 hours’ or ‘Last 2 weeks’). Click on any of the recordings to see if you agree with the species identification!
Conserving and observing migrants
Finally, remember that migration is physically demanding for birds because of the large distances flown, sometimes in bad weather or against the wind, and man-made structures present additional challenges and hazards. Here at the Delaware Nature Society, we do all we can to help migrating birds and other animals reach their destination. We try to reduce window strikes by adding clings and decals to make our windows more visible to birds, we follow Dark Sky practices by turning off unnecessary lights at night and installing downward-facing lights where possible and promote the use of native plants since these provide much more invertebrate food for hungry migrants.
We offer many free opportunities to witness the spectacle that is migration. Join us on our free bird walks held from 8am until 1030am September through October to see fall migrants as well as resident species on Tuesday mornings at Middle Run Natural Area in Newark, Delaware, and Sunday mornings at Bucktoe Creek Preserve near Kennett Square, Pennsylvania. Or visit our Bird Banding station at Bucktoe Creek Preserve on Wednesday mornings through November if the weather is amenable. We also run a daily hawk watch on the top of the hill at Ashland Nature Center in Hockessin from 9am until 4pm September through November, where our professional counter and volunteers collect data on the numbers of each species of hawks, falcons, vultures and eagles cruising overhead. The view from the hilltop as the leaf color changes can be spectacular and the company is convivial, so drop on by and check it out!
