Bird Banding

All posts tagged Bird Banding

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

Sparrows are a mystery to most non-birders (and many birders too!) and it’s not hard to see why. The great majority of them are small, brown streaky birds that at this time of year are usually just glimpsed as they disappear into a tangle of undergrowth, so much so that sparrow sightings often get lumped into the catch-all category of ‘Little Brown Bird’ (hastily scribbled as ‘LBB’ in field notebooks from here to Alaska).

This is a great pity as sparrows are an under-appreciated group of birds in my opinion, and Delaware is awash with them during the winter because several species that breed as far away as northern Canada flood into our area and flock together with our resident sparrows. Tangled brush piles and weedy fields might not be attractive to an average human but they are very popular with sparrows who love to scuffle through them in search of seed as well as take cover in them if a hawk appears. On a good winter’s morning you might see more than half a dozen species of sparrow just by slowly walking along the edges of these brush piles and fields and waiting for them to appear.

A simple first step to identifying sparrows is to look at their breast as this lets you place them into one of two broad categories: those with streaked breasts and those with unstreaked breasts. The collage below is composed of sparrows banded during DNS’s Bird Conservation Program and up close you can see the differences between species in breast patterning, as well as the eyebrow stripes, moustaches and thin crown stripe found in many sparrows.

Top row (L to R). Song, Fox, Savannah 2nd row. Lincoln’s, Field, American Tree (showing ‘stickpin’ in breast) 3rd row. Swamp, Chipping (winter), Slate-colored Junco 4th row. White-crowned, White-throated (adult), White-throated (immature)

The collage below shows the diversity of sizes, shapes and colors seen in sparrows’ beaks. For example, the beak of Song Sparrows is intermediate in length and depth while Fox Sparrows have a short but stout beak and both Lincoln’s and Swamp Sparrows have long, thin beaks. Some sparrows have all-brown beaks while others have beaks that are gray (White-throated), orange (Field), pink (Junco) or jet black (Chipping Sparrow during the breeding season). The American Tree Sparrow has the most distinctive beak of all, being dark brown above but yellow below. There is also quite a lot of variation in the angle of the forehead, the size of the eye, and the curvature of the upper beak.

Top row (L to R). Song, Fox (with 2 ticks!) and Field 2nd row. Chipping (summer), Chipping (winter), Savannah 3rd row. Lincoln’s, Swamp, American Tree 4th row. White-throated, Slate-colored Junco, White-crowned (immature).

Hopefully these photographs have convinced you that sparrows are more different and beautiful than you had thought. My advice is to slowly explore the undergrowth on a crisp, still winter’s morning and try to get a good look at every species you see. Rest assured, you will be rewarded!


By: Ian Stewart, Ornithologist

Delaware birders are out in full force at this very moment and one of their main targets is migrating warblers. Warblers are small, colorful songbirds which flit actively from tree to tree picking off insects with what the field guides usually describe as thin pointed beaks (also known as ‘bills’). But are warbler beaks really all small and pointed? We have handled several warblers during the Delaware Nature Society’s bird banding project and a closer view reveals a surprising amount of variation in the size, shape and color of their beaks.

The Northern Parula is one of the smallest warblers and has a very thin and pointed beak which it uses like fine tweezers to glean tiny arthropods from leaf surfaces.

Northern Parula

Northern Parula

The Prairie Warbler also has quite a sharp beak but it is shorter and more rounded than the Parula’s. Its beak is jet black unlike many of the other warblers which have brownish two-toned beaks with the upper mandible being darker than the lower.

Prairie Warbler

Prairie Warbler

The Mourning Warbler has a fairly substantial bill for a warbler. Mourning Warblers tend to feed on or near the ground and perhaps eat larger insects or grubs.

Mourning Warbler.

Mourning Warbler.

Waterthrushes are relatively dull, streaky warblers that live along streams where they pick arthropods from the surface of the mud and rocks. There are two species, the Louisiana and the Northern, which look very similar but can be partly distinguished by their beak length. The Louisiana was once known as the ‘large-billed waterthrush’ and you can see from these photos that their beak is indeed longer and a little heavier than the Northern.

Louisiana Waterthrush

Louisiana Waterthrush

Northern Waterthrush

Northern Waterthrush

The American Redstart has an unusual beak for a warbler. When seen from above (or more commonly, from below!) its beak is broadly triangular and looks more like that of a flycatcher than a warbler (see the photo below). It’s probably no coincidence that Redstarts often feed by leaping off branches and grabbing insects in mid-air. The conspicuous bristles around the base of their beak may help them trap these insects.

American Redstart (left) and Northern Waterthrush Beaks

Comparison of beak thickness in American Redstart (right) and Northern Waterthrush (left)

Another warbler with an unusual beak is the Yellow-breasted Chat. The Chat is a large, stocky bird that some people do not even consider a warbler, and it has a correspondingly huge, stout beak with a rounded upper mandible. Chats have such a big beak that they can chomp on insects such as grasshoppers that that are too big for the other warblers and can also eat berries.

Male Yellow-breasted Chat

Male Yellow-breasted Chat

Insects and other arthropods are the staple food of all warblers and yet the variation in the size and shape of their beaks suggests that each species eats different prey. This partly explains why some species are usually seen actively hunting in the upper canopy of either deciduous or pine trees while others creep slowly around on the ground, perhaps waiting for an arthropod to emerge. Warblers are passing through Delaware as we speak so next time you see one, take a good look at its beak and see if you can guess what it feeds on!

By Ian Stewart, Ornithologist

Bird banding is in full swing at both Ashland Nature Center and Bucktoe Creek Preserve and our mist-nets are becoming dominated by Gray Catbirds! Gray Catbirds (Dumetella carolinensis) are grouped with Northern Mockingbirds and Brown Thrashers as ‘mimic-thrushes’ as all three are slender thrush-like birds with long tails and loud, elaborate songs. Indeed, catbirds get their name because of the peculiar cat-like ‘miaow’ call they often give while hidden low in a bush! Catbirds are by far the most common of the three mimic-thrushes however, and can be so abundant that many birdwatchers don’t give them a second glance. This is a pity, because catbirds have several interesting features which are particularly obvious when you are holding them during the banding process.

The first of these is the conspicuous rictal bristles around the base of their bill. Several other groups of birds have rictal bristles (especially flycatchers) and although their exact purpose is unknown they are thought to either have a sensory function or to prevent captured insects from scratching a bird’s eyes while they are being held in their bill.

Four rictal bristles can be seen at the base of this Gray Catbird's bill.

Four rictal bristles can be seen at the base of this Gray Catbird’s bill.

The second distinctive Catbird character is their crimson ‘crissum’. This is the patch of feathers underneath their tail which isn’t always easy to see in the field as Catbirds tend to stay fairly low to the ground. The third interesting plumage character of Catbirds, which can also be seen in the picture below, are the fairly obvious growth bars in their outer tail feathers. Growth bars appear as alternating light and dark bands and each pair of bands represents one 24 hour period of feather growth.

Underside of a Gray Catbird showing the crimson crissum and growth bars in the outer tail feathers.

Underside of a Gray Catbird showing the crimson crissum and growth bars in the outer tail feathers.

Not surprisingly, Catbirds were by far the most frequently caught species during the pilot banding project we conducted last summer at Ashland and Bucktoe. In just 3 months we caught 152 catbirds, of which 87 were juveniles likely hatched locally. So far this year we have recaptured 3 of the catbirds we banded last year and hope to recapture even more as the season progresses. It’s truly amazing to think that these 3 birds spent their winter over a thousand miles away in the south-eastern US or the Caribbean and yet came back to the same few hundred acre spots in DE and PA the following year!

The number on this metal leg band showed that this Gray Catbird was banded the previous year.

The number on this metal leg band showed that this Gray Catbird was banded the previous year.

So be sure to take a longer look at a Gray Catbird next time you see one. They are more interesting than you might think!

Public bird banding sessions are held at Ashland Nature Center on Monday and Bucktoe Creek on Wednesday, both from 8am – 11am, though banding does not take place if it is raining or windy, out of concerns for the birds’ safety.

Note that there will be no banding this Monday (May 30th) due to the Memorial Day Holiday.