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Ian Stewart

A major analysis published last week (Rosenberg et al. 2019, Science, downloadable by scrolling down here) makes depressing reading for anyone interested in birds or in nature in general. A team of leading North American researchers analyzed almost 50 years of data from multiple sources and calculated that about 3 billion birds (= 3 thousand million!) have been lost from the continent since the 1970s. This staggering total suggests that over 1 in 4 North American birds have disappeared in less than half a century. Some groups of birds have been hit especially hard, with over half (53%) of all grassland birds disappearing as more and more of their habitat is plowed under to make way for agriculture or development. Shorebirds are close to the hearts of many Delawareans since they famously stop to refuel in the Delaware Bay on their way north to breed and yet these are among the most strongly declining birds, with a drop of 37% in 50 years. The bejewelled warblers, those colorful songbirds which symbolize migration for many birders, have dropped by 38%.

A Rusty Blackbird, one of several rapidly declining bird species

Some of the report’s findings simply confirmed the sad stories recounted by long-time Delaware birders that species which used to be merely uncommon are now very hard to find, like the Rusty Blackbird. However, some of the other findings were much more surprising and perhaps more troubling because they revealed serious declines in groups of birds usually taken for granted as ‘common’ like blackbirds (44%), finches (37%) and sparrows (38%). It is probably not a coincidence that almost all of these species feed their nestlings on insects, another major taxon that has seen dramatic declines.

A male Red-winged Blackbird breeding in a meadow at Coverdale Farm Preserve.

The report wasn’t all doom and gloom however. Waterbirds (ducks and geese) have shown a resurgence (+56%) thanks to better management and protection of wetland and marsh habitats based on millions of dollars raised by the sale of Duck Stamps to hunters and non-consumptive users as well as federal and state wildlife grants. Several birds of prey have also rebounded thanks in part to the ban on DDT, including a remarkable 300% increase in the numbers of the fish-eating Osprey. These success stories show that bird declines can be reversed if we act quickly enough to protect and preserve their habitats since the loss or degradation of their breeding, wintering or migratory habitats is the root cause of almost all bird declines.

Birds provide many ecological benefits like seed dispersal, pollination and control of arthropod pests but are also a source of everyday enjoyment for millions of North Americans who enjoy bird watching or feeding birds. Birds are also an excellent way to stimulate an interest in nature, especially among children, because they are active during the day and present in all four seasons, and many have colorful plumage or attractive songs. In short, birds are perhaps the most visible and recognizable component of most North American ecosystems, and if they are in such a serious decline then many other parts of the ecosystem probably are too. A loss of 3 billion birds in less than 50 years is simply not sustainable.

A mixed flock of sparrows in a typical suburban yard in winter. One day, this may not be a common sight.

Although the challenges birds face are large and on a continental scale, there are several fairly simple ways that you can help birds in your own yard or neighborhood. Try this excellent list from Cornell University!

 

Ian Stewart

One of my favorite books is Arthur Conan Doyle’s ‘The Hound of the Baskervilles’, in which a mysterious beast pursues Sherlock Holmes through the eerie mist of an English moor. Driving the back roads of northern Delaware in the early morning reminds me of this gloomy setting because many of the trees are now shrouded with ghostly tents.

A typical scene in Delaware in late summer

These tents were constructed by the fall webworm, which is the caterpillar of an innocuous white moth (Hyphantria cunea). This native moth which lays hundreds of eggs on the underside of a leaf during the late spring and early summer then promptly dies. The eggs hatch out into tiny caterpillars which soon build extensive, multi-layered webs around groups of leaves for protection and perhaps insulation. The caterpillars start chomping away on the leaves within each web until all that remains is a skeleton of the indigestible frame of the leaf and a large pile of dark brown frass (feces).

The droppings pile up below a cluster of fall webworms

Once the caterpillars become large enough they chew their way out of the web and keep munching on leaves before overwintering as a pupa attached to the bark or in the leaf litter below the tree, and emerging as an adult moth the following spring. Unlike many butterflies and moths, fall webworms are not specific to a small range of trees or bushes, and have been recorded on almost 100 different host trees. My impression is that webs are most common on black walnuts and black cherries, perhaps because it is easier to build a web on these trees because they have long drooping branches with multiple leaflets. Or maybe it just reflects the fact that both these trees are common in our area? I also think the number of webworms is increasing each year and have seen several totally denuded trees this summer.

Skeletonized leaf of a hickory after the webworms have left

Contrary to popular opinion, fall webworms are not the same species as tent caterpillars, although they do share certain features. The eastern tent caterpillar (Malacosoma americanum) also builds extensive webs in which it chomps away at the leaves, and is also the larval form of an unremarkable dull moth (somewhat ironically given how conspicuous the caterpillars are!). However, the tent caterpillar is active in spring and usually builds its tents in the crotch of a branch whereas the fall webworm’s webs are usually at the end of a branch.

Interestingly, one would think that both tent caterpillars and fall webworms would be a magnet for hungry birds, especially because their appearance coincides with spring and fall migration respectively. The webs are easy to find and contain dense clusters of juicy caterpillars, which are a major food source for many small birds. Surprisingly however, very few birds seem to eat them apart from orioles and cuckoos, and it may not be a coincidence that these both have long thin beaks which they can poke through the layers of webbing without risking it sticking on their eyes. It may also be that the caterpillars are unpalatable because they have long hairs (especially the fall webworm, see the photo below) or contain toxic substances. Perhaps birds prefer to wait until they become moths the following year and eat them then. The caterpillars are not entirely safe within the web however, as several species of predatory invertebrates will try to penetrate it including wasps, ladybugs and most dramatically, the fiery searcher (Calosoma scrutator), a large and colorful beetle which climbs trees at night to feast on clusters of caterpillars.

Hairy caterpillar of the fall webworm

Fiery searcher photographed by Joe Sebastiani

Although many homeowners become concerned when a tree in their yard becomes coated with webs, there is no reason to be alarmed. Fall webworms usually do not do the tree any long-lasting damage because only a fraction of the leaves are eaten, so the tree can still photosynthesize for the rest of the summer and thereby store enough nutrients in the root to get it through the winter. Next year the new leaves will grow in just fine. Although trees with heavy infestations can appear almost leafless (like the one below), in the vast majority of cases fall webworms are nothing more than an unsightly pest and it’s not worth trying to remove them, especially as they are usually high in the tree. Instead, why not just admire these lowly creatures for building their own homes?

A heavy infestation of fall webworm

Ian Stewart & Lori Athey

Now that spring is here many Delawareans are enjoying the colorful wildflowers blooming in their backyard, local parks and road sides. Unfortunately, the great majority of those currently flowering are alien weeds which were either deliberately or accidentally introduced by Europeans. These plants found themselves in a new environment with few or no natural enemies and spread rapidly across our area. Each weed produces hundreds if not thousands of seeds and an entire backyard can be riddled with them in just a few years.

The three most common yellow-flowered weeds have been covered in a previous blog (http://blog.delawarenaturesociety.org/2015/05/06/the-not-so-mellow-yellows/) and this follow-up blog highlights some of the other visually-appealing wildflowers that people may not realize are aggressively invasive aliens.

Three common backyard weeds stay low but spread rapidly to form sun-blocking carpets that inhibit or prevent the growth of any native seeds beneath them. Speedwell (Veronica sp.) is one of the first wildflowers to emerge and its four-petaled circular blue flower can be seen as early as March. There are several species of speedwell but most are alien. Ground ivy (Glechoma hederacea) produces dozens of tiny purple flowers and spreads by underground rhizomes which makes it especially difficult to control since pulling one part of the plant will not suffice. Clover (Trifolium sp.) is particularly common in farm fields, perhaps because it may have been introduced as livestock feed, but is now ubiquitous in urban and suburban settings. Clovers have three leaves, each with a distinctive white chevron, though finding one with four leaves may bring you luck! There are two sister species, the red and white clover, which are named after the color of their flower.

Speedwell (Left) and Clover (Right)

Ground ivy

Two striking members of the Mint family also stay quite low to the ground but are easily seen because they often grow in large patches. Purple deadnettle (Lamium purpureum) and henbit (L. amplexicaule, also known as clasping deadnettle) often grow together in fields and backyard although the former is much more common.

purple deadnettle

Henbit

Finally, three conspicuous white-flowered members of the Mustard family are widespread throughout the Piedmont. Garlic mustard (Alliaria petiolate) and roadside penny-cress (Thlaspi alliaceum) are both knee-high single-stemmed weeds which form large clumps in sunny areas, while hairy bittercress (Cardamine hirsute) is quite a bit smaller and branches into multiple small flowers.

Garlic mustard

roadside penny-cress

Penny-cress up close

Purple deadnettle (on left) and hairy bittercress (on right)

These alien wildflowers are especially problematic because they bloom in early spring and may have already produced seeds before householders begin mowing. Although it is an uphill battle, most weeds can be controlled by hand-pulling them before they go to seed, especially if the whole root system is removed.  Repeated early mowing or weed-whacking will deplete the weeds’ resources before they even flower. If you have a large yard or field an alternative option is to gradually convert it into a meadow with long grass and native wildflowers which is left standing throughout the winter and early spring. This helps to restrict early-growing weeds like ground ivy and deadnettle by reducing the amount of sunlight they receive.

Once you have removed the alien weeds you can replace them with native wildflowers which are much better for wildlife, especially our declining pollinator insects as well as the animals that feed on them. A perfect opportunity is the Delaware Nature Society’s Native Plant Sale which is held at Coverdale Farm in Greenville. It starts with a member’s-only day on Thursday May 2nd (1pm-7pm; though you are welcome to attend and join in person) and is then open to the public Friday May 3rd (3pm-7pm) and Saturday May 4th (9am – 3pm). Admission is free and there will be plenty of staff and volunteers present to answer any questions about plants and help you load them into your car!

The full catalog is online here but just to whet your appetite, here is a selection of groundcover plants which are tough and fast-growing and have a decent chance at outcompeting those pesky weeds!

Dry sunny location

Andropogon virginicus (Broom Sedge) grass

Coreopsis verticillata (Whorled Tickseed) perennial

Geum fragarioides (Barren Strawberry) evergreen perennial

Phlox subulata (Moss Phlox) evergreen perennial

 

Dry shaded location

Antennaria plantaginifolia (Woman’s Tobacco Pussytoes) semi-evergreen perennial

Chasmanthium latifolium (Wild Oats) grass

Geranium maculatum (Wild Geranium) perennial

Polystichum acrostichoides (Christmas Fern) evergreen fern

 

Moist shaded location

Asarum canadense (Wild Ginger) perennial

Osmundastrum cinnamomeum (Cinnamon Fern) fern

Phlox stolonifera (Creeping Phlox) perennial

Zizia aurea (Golden Alexanders) perennial

 

Moist to wet sunny location

Carex cherokeensis (Cherokee Sedge) grass

Eupatorium perfoliatum (Boneset) perennial

Iris versicolor (Blue Flag) perennial

Panicum virgatum (Switchgrass) grass

 

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