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Ian Stewart

These are the opening words of the poem ‘To a mouse’, written by the legendary haggis-eating Scottish poet Robert Burns in 1785 (which also contains the famous line oft-paraphrased as ‘The best-laid schemes of mice and men go often askew’). Although this is an apt description of mice it is also used to refer to all manner of small, obscure and reclusive animals and feather mites fit perfectly into this category.

Most people have never heard of feather mites which is hardly surprising. They are tiny brown arthropods which spend most of their lives flattened along the vanes of bird wing feathers where they were assumed to scavenge on feather debris and oily secretions and perhaps even rasp away at the feathers themselves. However, a remarkable study published last summer (Doña et al. 2018) examined the contents of mites’ stomachs using high-power microscopy and DNA analysis and found that their main food was fungi, and perhaps also bacteria and oil produced from the birds’ preen gland. Whether this means feather mites harm their hosts or are simply commensal remains to be seen.

Birds are assumed to acquire feather mites through physical contact with their parents while they are still in the nest, although they could also pick up mites from bumping into other birds at feeders or sharing the same dust bathing sites. Mites are quite easy to see if you are holding open a bird’s wing although with the naked eye they just look like a cluster of small dots (shown below).

We gained a whole new appreciation for these creatures when Shannon Modla of the University of Delaware kindly photographed some Gray Catbird feather mites under a light microscope. The magnified views show that they are long and thin with two pairs of legs at the front of their body and two pairs at the back (image below). The darker mites on the left and below are probably older mites with a hardened exoskeleton while the paler one on the right is probably a younger mite that has just molted.

Shannon was then able to view them under a powerful electron microscope and got some incredible images of their head as well as an egg (below).

To try to gain some insights into the biology of these enigmatic creatures we have been scoring the number of feather mites present on birds handled during the Delaware Nature Society’s Bird Banding project. Our simple questions were which bird species are most likely to have mites and whether the number of birds with mites varies according to the time of year.

Our first finding was that feather mites are quite common. We examined 448 birds belonging to 48 species and found that almost half of them (203 birds from 37 species) had mites on at least one of their wing feathers. We also found the proportion of birds with mites varies a lot between species. Over 75% of the Slate-colored Juncos, House Finches and Downy Woodpeckers that we examined had feather mites yet fewer than 15% of Ruby-crowned Kinglets, Common Yellowthroats or House Wrens had them. We also found that the proportion of birds with mites stayed quite consistent across the year with a noticeable peak in May.

This year we will be gathering more data on mites from the birds we band and then try to figure out why some birds are more likely to have mites than others, and why some have lots of mites while others have very few. Is it related to their body size perhaps, or how social they are, or maybe whether their beak is small and pointed enough to preen away the mites? So watch this space for updates on this new and fascinating DNS research project!

DNS has plenty of birding opportunities coming up soon, so sign up and enjoy the outdoors!

The Great Backyard Bird Count ~ Coverdale Farm Preserve

The Great Backyard Bird Coount: Kent County Tour ~ Abbott’s Mill Nature Center

Owls and Other Winter Raptors ~ Ashland Nature Center

 

Ian Stewart

Happy New Year everyone! If you’re looking for an interesting New Year’s Resolution to get you outdoors, why not seek out and learn about a different tree every month? This is exactly the time of year to spot one of Delaware’s most distinctive trees – the Osage orange.

The Osage orange (Maclura pomifera) is a small to medium-sized deciduous tree native to the Midwest that was originally restricted to a relatively small stretch of Arkansas, Oklahoma and Texas. It is not related to oranges but is in the Mulberry family. The name refers to the bright orange color of its wood and the Osage Nation, a midwestern Native American tribe who used the wood for making bows and apparently supplied early settlers with young plants.

The exposed orange roots of a fallen Osage

Although their original range was small, Osage oranges are now found throughout the lower 48 states after lines of them were planted to provide windbreaks in flat open landscapes such as farmland and isolated homesteads. Lines of Osages were also planted throughout the rest of the country to act as natural thorny fencerows for housing livestock and to delineate driveways and land borders, which is why you most often find Delaware Osages arranged in rows on either side of old country roads. Coverdale Farm Preserve’s famous ‘Avenue of the Osages’ contains no fewer than 72 of these striking trees which were probably planted over a hundred years ago.

Coverdale Farm’s famous ‘Avenue of the Osages’, with fallen fruit in foreground

Gnarly, orange-tinged bark of an Osage

The easiest time of year to identify Osage oranges is in the middle of winter as the bare trees now reveal their distinctive gnarled orange-tinged bark made up of many twisted strips. Some trees still bear their large green fruit, commonly known as ‘monkey brains’, although most of these have now fallen to the ground. Be careful – if they fall on a sidewalk or road they become a slippery hazard to pedestrians and motorists alike!

Osage orange fruit with knobbled surface

Interior of an Osage fruit with some seeds

Osages occur as either male or female trees but only the female trees produce the softball-sized fruit which contains several small seeds within its gooey white flesh. Although the fruit is edible almost all animals ignore it as it is tough, unpalatable and exudes latex, so the clusters of monkey brains simply remain where they fall until they decay. Squirrels do eat the seeds however, which may be why you see so few young trees mixed in with the old ones.

Interestingly, almost every Osage I see has a poison ivy vine growing up its trunk, perhaps because the vine finds it easy to grip onto the furrowed bark. Next time you are a passenger in a car being driven along a country lane, try to spot some rows of Osage oranges. If you spot some it might make you resolve to learn about our local trees in 2019!

This Osage was cut down at Coverdale and has about 90 growth rings, suggesting it was at least 90 years old. The poison ivy vine seen in cross-section on the left of the trunk had 19 growth rings so it had been attached for many years.

Ian Stewart

Every fall birdwatchers throughout the eastern United States wait anxiously by their computers for an email containing this year’s Winter Finch Forecast http://jeaniron.ca/2018/wff18.htm. For almost 20 years now Ron Pittaway, a former naturalist at Algonquin Provincial Park in Ontario Canada, has been predicting whether this group of small, seed-eating birds that breed in Ontario remain there during the winter based upon how successful the cone crop was that summer. Simply put, if the trees produced a lot of seeds then the finches will have enough food to survive the winter and will stay up north, but if the cone crop was poor they will have to fly south to find food and will ‘irrupt’ into the northern United States or maybe even further south.

Remarkably, Ron’s forecast is usually correct so local birders were thrilled to read his prediction that finches would be travelling south this winter because the cone crop in Canada was poor. Sure enough, about 2 weeks ago people throughout Delaware and south-eastern Pennsylvania started seeing flocks of Purple Finches at their feeders! These look a bit like our resident House Finches but the males are raspberry-colored over their whole body while the females and immature birds are heavily streaked below and have white stripes on their face. Purple Finches are attracted to black oil sunflower seed, especially if it is piled on a horizontal platform feeder.

A flock of Purple Finches at a platform feeder

The Delaware Nature Society’s bird banding program has confirmed that this is an irruption year for Purple Finches. So far this fall we have banded no fewer than 40 of these birds, compared with just 5 in the winter of 2016 and none at all last winter.

Male House Finch (left) and Purple Finch (right) banded this fall

Now people across our region are seeing a second species of winter finch at their feeders, the Pine Siskin. This small, streaky finch has yellowy-green wing patches and a very thin beak which it uses to pry nyjer (thistle) seeds from finch socks or hanging feeders with narrow holes.

Pine Siskin feeding on ground (Photograph by Hank Davis)

The thin beak of a Pine Siskin

Whisper it quietly but this winter we may see two more highly-prized finches which usually remain far to our north. The first of these is the Redpoll, a small streaky finch with a red forehead that flocks in weedy fields and congregates at nyjer feeders. The second is the majestic Evening Grosbeak, a striking yellow, black and white version of our familiar Cardinal which is attracted to platform feeders baited with sunflower seed

All of the above winter finches readily come to bird feeders and best way to attract them to your yard is to provide a variety of seeds in different types of feeders, like hanging tubes of either black oil sunflower or nyjer coupled with platform feeders filled with sunflower seeds or millet. Try visiting Wild Birds Unlimited in Hockessin for a large selection of seed mixes and feeders.

Flock of Siskins at a hanging feeder (Photograph by Hank Davis)

Another two irruptive winter finches that are much sought after by birdwatchers are the crossbills. The Red Crossbill tends to occur in pines and the White-winged Crossbill in spruces and larches. These intriguing birds are unique in that their upper and lower beaks are ‘crossed’ and are used to prise open pine cone scales to get to the seed within. Crossbills do not usually come to seed feeders but if you want to attract them you could try pulling the old ‘salt block trick’. Apparently they are very fond of salt and can be attracted to platform feeders using chunks of the salt blocks that farmers leave out for cattle and horses!

The winter of 2018/2019 could be a memorable year for winter finches in Delaware, so be sure to take full advantage of it. The best places to search are weedy fields and stands of cone-bearing pine trees in public parks or cemeteries, but you are just as likely to see them at the feeders in your back yard or the Ashland Nature Center bird blind. And maybe consider dropping by our free bird banding sessions to see if you are lucky enough to see a winter finch up close. Bird banding takes place through November every Monday at Ashland Nature Center and every Wednesday at Bucktoe Creek Preserve near Kennett Square, 8am-11am.

 

Ian Stewart

Jewelweed is a colorful native annual wildflower that is common in damp marshy areas where it grows as a thin bush about 4 feet high. It is also known as ‘touch-me-not’ because of its curious habit of expelling its projectile seeds when the flowers are handled or brushed against. Jewelweed is a classic folk remedy because the juice of its leaves and stems is a well-known antidote to stings and rashes from stinging nettle, which it often grows close to.

Jewelweed growing along the boardwalk at Ashland

Many Delawareans are familiar with jewelweed as it is often found in shaded suburban gardens and parks, but few people realize that there are two species and they usually grow right next to each other! The most common is spotted jewelweed (Impatiens capensis), which is also known as orange jewelweed. This has bright orange petals densely covered with red spots and a long ‘nectar spur’ which curls along the bottom of the flower. The second, less-common species is yellow jewelweed (Impatiens pallida), which is also known as pale jewelweed. This has larger, yellow flowers with only a smattering of red spots and a shorter nectar spur which dangles downward. The leaves of yellow jewelweed have more veins and are more deeply toothed than those of the orange jewelweed. In my experience, spotted jewelweed outnumbers yellow by about 5 to 1.

Side by side views of spotted (left) and yellow (right) jewelweed showing the differences in petal pattern, the length and angle of the nectar spur, and leaf venation

Jewelweed is pollinated by both hummingbirds and bees and watching these insects crawl into the depths of the flower to access the nectar pooled up in the spur is a fun way to spend a sunny afternoon! If you’re very lucky you may get to see a hummingbird feeding from the nectar spur.

A bee burrows into a jewelweed flower in search of nectar

The bee’s back is now coated in pollen from the pollen stalk dangling above it. The bee may now pollinate the next jewelweed it enters!

Both jewelweeds have a long blooming season from late spring through the early fall and are an attractive native wildflower to plant in a damp, shaded corner of your yard to attract pollinator insects and hummingbirds.

Learn more about how you can garden for native plants and wildlife by certifying your yard as a wildlife habitat through the Delaware Nature Society

https://www.delawarenaturesociety.org/what-we-do/protecting-habitats-wildlife/garden-for-wildlife/