Category Archives: Birds of Prey

On Finding Pellets

Red-tailed hawk casting a pellet, 2018 (photo by Chad+Chris Saladin)

22 January 2023

This red-tailed hawk is not consuming the lump near his mouth. He’s casting a pellet of indigestible bones, fur and feathers that came up from his gizzard. Pellets are a normal by-product of digestion in birds of prey. If you find one, it can tell you what the bird was eating.

We always find pellets during annual maintenance at the Pitt peregrine nestbox including these three found during our 9 January visit (paperclip for scale). The pellets can be many months old.

Peregrine pellets from Cathedral of Learning nestbox, 9 Jan 2023 (photo by Kate St. John)

A closeup shows feathers and bones (no fur*) but is not very enlightening due to the pellet’s age. Fortunately I stored the pellets in a ziploc bag. After they thawed a small fly appeared inside the bag, hatched from eggs laid on the pellet in much warmer weather. Ewww!

Closeup of peregrine pellet (photo by Kate St. John)

I imagine the pellets came from Morela since the green perch is one of her favorite places to rest and digest.

Morela casting a pellet, 17 Dec 2021 (photo from the National Aviary snapshot camera at Univ of Pittsburgh)

Peregrine pellets are slightly longer than a paperclip. Some birds make much larger pellets.

On a hike at Audubon Greenway Conservation Area last Wednesday we found a surprisingly large pellet containing fur, bones and a big tooth. It was so large that we wondered if a bird could produce it. I didn’t pick it up but it looked as though it could span my palm.

Pellet found at Audubon Greenway, 18 Jan 2023 (photo by Kate St. John)
Alternate view of pellet found at Audubon Greenway, 18 Jan 2023 (photo by Kate St. John)

A Google search revealed that great horned owl pellets are 3 to 4 inches long, usually cylindrical and tightly compacted. This one may have opened up because it was soaked by heavy rain.

Great-horned owl clutching a feather (photo from Wikimedia Commons)

So what did the owl eat? Whose big tooth was that?

Learn more about owl pellets at The Owl Pages: Digestion in Owls.

* p.s. There is no fur in peregrine pellets because they don’t eat mammals, only birds.

(photos from Chad+Chris Saladin, Kate St. John, the National Aviary snapshot camera at Univ of Pittsburgh and Wikimedia Commons)

Seen This Week

Sunrise, 11 Jan 2023 (photo by Kate St. John)

14 January 2023

The sunrise was gorgeous and cold last Wednesday when a group of us decided to walk at Jennings in Butler County. We saw few birds but there were ice heaves, buttress roots on an elm, and the seeds of old man’s beard (Clematis drummondii).

Ice heave at Jennings, Butler County 11 Jan 2023 (photo by Kate St. John)
Elm tree with buttress roots, Jennings, Butler County, 11 Jan 2023 (photo by Kate St. John)

When old man’s beard is in bloom it’s called virgin’s bower, transforming it from a young woman to an old man in a matter of months.

Seeds of Virgin’s bower, a.k.a. Old man’s beard, Jennings, Butler County, 11 Jan 2023 (photo by Kate St. John)

My friends who live north of the city have not seen many dark-eyed juncos at their feeders this winter, but juncos are definitely present at the Frick Park Environmental Education Center. Charity Kheshgi posted photos of our recent trip to Frick.

(bird photos by Charity Kheshgi embedded from Instagram, all other photos by Kate St. John)

Golden Eagle Special on WQED, Dec 21

Golden eagle at the Allegheny Front Hawk Watch, 2 Nov 2016 (photo by Steve Gosser)

19 December 2022

Golden eagles (Aquila chrysaetos) occur worldwide in the northern hemisphere but are quite rare in Pittsburgh though we see them on migration at the Allegheny Front. Their stronghold in North America is in the American West but now the birds face many threats.

Pittsburgh conservation filmmakers, David and Melissa Rohm of Wild Excellence Films, went to Wyoming to learn about the challenges the eagles face and meet the people working to save them. Their film, Golden Eagles: Witnesses to a Changing West, will air on WQED this coming Wednesday, 21 December 2022 at 10:00pm.

Coming to WQED on Wednesday 21 December 2022 at 10pm

In the film we learn that golden eagles prefer wide open spaces without human interference so when we move in, they move out. They’ve disappeared from many areas heavily disturbed by humans and, according to Birds of the World, most North American nesting populations are declining or below carrying capacity due, in part, to anthropogenic related mortality.

Golden eagle range map (image from Wikimedia Commons)

Watch eagle researchers rappel down cliffs to band golden eagle chicks. Visit wildlife rehabilitation centers where eagles are treated for lead poisoning. Hear Indigenous people’s connections to the largest eagle in the American West.

Don’t miss Golden Eagles: Witnesses to a Changing West on WQED on Wednesday, 21 December 21, at 10pm.

(photo of golden eagle at the Allegheny Front by Steve Gosser, map from Wikimedia Commons, remaining images from Wild Excellence Films, click on the captions to see the originals)

Eagle Season is Heating Up

Bald eagle at Hays, 4 December 2022 (photo by Dana Nesiti, Eagles of Hays PA)

15 December 2022

Even though it’s December and the weather will only get worse, western Pennsylvania’s bald eagles are gearing up for the nesting season with plans to lay eggs in February.

Established pairs are hanging out together and guarding their territories. Interlopers are testing the limits to see if they can claim an existing site. Subadult eagles are roaming the rivers, trying to steal prey from each other and adults.

Dedicated eagle watchers are already stopping by the viewing sites to catch a glimpse of the action.

At the Hays viewing area on 4 December, Dana Nesiti of Eagles of Hays PA found “both eagles above the nest this morning at first light” (photo at top). On 20 November he saw a prey item stolen twice:

At 9:17am a Peregrine Falcon flew past the nest upstream carrying prey. The male gave chase and they both flew up and over the hillside. 9:35am the male comes flying back carrying prey with a sub adult hot on his tail feathers. They flew down past the stick store and we saw them dive, both eagles came circling back towards the nest. Now the sub adult was carrying the prey and the male was chasing him.

Dana Nesiti, Eagles of Hays PA, 20 Nov 2022

Here a subadult carries prey that was probably stolen twice on 20 November.

Subadult carrying prey at Hays, 20 Nov 2022 (photo by Dana Nesiti, Eagles of Hays PA)

Hays is just one of at least five nesting territories in our area:

Stop by your local bald eagle patch to check out their recent activity.

It may be cold outside but eagle season is heating up.

Check out Eagles of Hays PA on Facebook for more Hays eagle news.

(photos by Dana Nesiti Eagles of Hays PA, used by permission)

In Which Kites Become Planes and Birds

Box kite at International Kite Festival, India, 2013 (photo from Wikimedia Commons)

25 November 2022

Kites sometimes fly with the birds. A distant raptor soars at center-bottom of the photo above. Kite + Bird.

In 1914 this kite was becoming a plane. Kite = Plane.

Colonel Granville Ryrie and a box kite, Australia, 1914 (photo from Wikimedia Commons)

Some kites are birds. More than two dozen species of raptors are named “kite” including the Mississippi kite (Ictinia mississippiensis) of North America and the red kite (Milvus milvus) in Europe. Kite = Bird.

Red kite in flight (photo from Wikimedia Commons)

Putting them all together, Chris Darbey (@chrisddarbey) photographed a red kite with a jet contrail. Kite=Bird + Plane.

(photos from Wikimedia Commons, tweet embedded from @ChrisDDarby)

Eagles Die When We Kill a Weed

Bald eagle portrait (photo from Wikimedia Commons)

6 November 2022

In 1994 dozens of bald eagles were found convulsing, dead or paralyzed near Arkansas’ DeGray Lake. Autopsies revealed the eagles died of a new disease called avian vacuolar myelinopathy (VM) that manifests as brain lesions. The dying spread to Florida, Georgia, the Carolinas and Texas (hashed areas on the map below) and continues to this day. In 2021 scientists discovered what causes VM. It’s a chain of events that begins when we use an aquatic weed killer to control an invasive weed.

VM occurs in watersheds where A. hydrillicola colonizes H. verticillata. Watersheds where VM has been diagnosed (indicated by black crosshatching). Watersheds where H. verticillata has been confirmed to be colonized with A. hydrillicola are shown in red, and watersheds where A. hydrillicola has not yet been observed on H. verticillata are shown in yellow. Watersheds not yet screened for A. hydrillicola, but where H. verticillata occurs, are shown in green. This map, embedded from NIH, is current to fall 2019.

The invasive weed is hydrilla (Hydrilla verticillata) that spreads easily and clogs waterways. It’s a huge problem in many southeastern states, especially in Florida.

Hydrilla at Lake Seminole, Florida (photo from Wikimedia Commons)

Hydrilla hosts a cyanobacteria called Aetokthonos hydrillicola which does not produce toxins by itself(*). However when it comes in contact with bromide-containing aquatic weed killer, meant to kill hydrilla, it produces a neurotoxin.

Cyanobacterium on hydrilla produces a neurotoxin in the presence of bromide weed killers (subimage from diagram below + jug composed from spare parts)

Fish and waterbirds, including American coots, eat the hydrilla and consume the neurotoxin. Soon they develop VM brain lesions.

American coot eating hydrilla (photo from Wikimedia Commons)

Bald eagles and other predators eat the fish and coots, often preying on sick ones because they are easy to catch.

Bald eagle hunting an American coot (photo from Wikimedia Commons)

And so bald eagles develop brain lesions and die of vacuolar myelinopathy.

The AVM cycle begins with a cyanobacteria on hydrilla that develops a neurotixin when treated with bromide weed killer (diagram from Wikimedia Commons)

The way to stop the dying is described in this NIH article Hunting the eagle killer: A cyanobacterial neurotoxin causes vacuolar myelinopathy:

Integrated chemical plant management plans to control H. verticillata should avoid the use of bromide-containing chemicals (e.g., diquat dibromide). [The neurotoxin] AETX is lipophilic with the potential for bioaccumulation during transfer through food webs, so mammals may also be at risk.

— from NIH: Hunting the eagle killer: A cyanobacterial neurotoxin causes vacuolar myelinopathy

Thus if you use a bromide-containing chemical (e.g. diquat dibromide) to control hydrilla you will unintentionally kill bald eagles.

Diquat aquatic weed killer contains bromide which leads to AVM (image constructed by Kate St. John)

Other solutions for controlling hydrilla without herbicide are highlighted in Florida Today (article and video): Melbourne-Tillman harvests hydrilla to avoid herbicides.

Meanwhile bald eagles aren’t out of the woods yet because we don’t know how long it will take for the neurotoxins to clear from infected lakes.

For more information see the article that inspired this topic: Science Magazine: Mysterious eagle killer identified: A new species of cyanobacteria that lives on invasive waterweed produces an unusual neurotoxin.

(photos and diagram from Wikimedia Commons, map embedded from NIH; click on the captions to see the originals)


(*) The mystery was solved when scientists discovered that the toxin came from bromides that did not occur naturally. From NIH, Hunting the eagle killer: A cyanobacterial neurotoxin causes vacuolar myelinopathy: “Laboratory cultures of the cyanobacterium, however, did not elicit VM. A. hydrillicola growing on H. verticillata collected at VM-positive reservoirs was then analyzed by mass spectrometry imaging, which revealed that cyanobacterial colonies were colocalized with a brominated metabolite. Supplementation of an A. hydrillicola laboratory culture with potassium bromide resulted in pronounced biosynthesis of this metabolite. H. verticillata hyperaccumulates bromide from the environment, potentially supplying the cyanobacterium with this biosynthesis precursor.”

Easy Meals For Young Eagles

Buckhorn Mesa landfill, June 2013 (photo by Alan Levine, Creative Commons license via Flickr)

26 October 2022

Bald eagles are birds of prey that eat fish, right? Well, mostly fish. Bald eagles are opportunistic feeders that will grab what they can get. Most of the time they catch live fish but they’ll also pounce on ducks and coots, steal fish from ospreys, scavenge on roadkill and fight each other for tasty morsels.

Juvenile bald eagles are not skilled at fishing so many opt for easy meals found elsewhere, particularly at landfills. It may be junk food but it keeps them satisfied.

Juvenile bald eagle (photo from Wikimedia Commons)

On Throw Back Thursday read about bald eagles and landfills in this vintage article:

(photos from Flickr via Creative Commons license and from Wikimedia Commons; click on the captions to see the originals)

Working Birds

Peregrine falcon “Charlie” at work at Ramstein Air Base, Germany, Feb 2009 (photo from Wikimedia Commons)

5 September 2022

On Labor Day let’s honor working birds.

Pictured above is a bird at work in 2009, a peregrine falcon named Charlie whose job was to clear birds from the airfield at Ramstein Air Base, Germany. His full crop indicates that he’d already done his job that day but he was looking around anyway, just in case some birds came back.

Charlie is one of several working falcons who make it safe for flights to take off and land at Ramstein. Click on this link to see photos when Ramstein AB celebrated their falcon workers on Earth Day 2018.

And don’t miss this vintage article featuring Rufus, the Harris hawk who patrols Wimbledon. (Includes video!)

(photo from Wikimedia Commons)

Young Owls at Dusk

Barred owl juvenile, Frick Park, 23 July 2022 (photo by Charity Kheshgi)

27 July 2022

This spring a pair of barred owls (Strix varia) nested in Frick Park. The two nestlings fledged in June but won’t become independent until fall so Charity Kheshgi found all four family members when she looked for them last Friday. Here are the two youngsters at dusk.

Barred owl juveniles, Frick Park, 22 July 2022 (photo by Charity Kheshgi)

On Saturday she saw one juvenile, photo below and at top.

Barred owl juvenile, Frick Park, 23 July 2022 (photo by Charity Kheshgi)

And on Sunday both youngsters, one shown below.

Barred owl juvenile, Frick Park, 24 July 2022 (photo by Charity Kheshgi)

I went to see for myself and learned a helpful tip. If you’re looking for young owls at dusk, find the upset and shouting wood thrushes and robins. They will be dive-bombing the owl.

See more of Charity’s photos on Instagram.

(photos by Charity Kheshgi)

Cooper’s Hawk Family Grows Up

Juvenile and adult Cooper’s hawks, Frick Park, 14 July 2022 (photo by Charity Kheshgi)

25 July 2022

This April Charity Kheshgi and I noticed Cooper’s hawks nesting in Frick Park and wondered when their young would fledge. In “Cooper’s Hawk Nesting Questions” I concluded the young would fly by June 22-26 at the latest. They were even later than that because…

This month we checked on their progress every few days. On 3 July the pair had four thriving youngsters who were walking on branches and making short hops. (Not fledged yet?) By 8 July the young could fly but they refused to leave the vicinity of the nest.

All four were still there on 14 July, flying well and begging near the nest. “Feed me!” Their father baby-sat, above, while their mother was out hunting. The young were very alert, especially when they saw “mom” coming home.

Two of four juvenile Cooper’s hawks, Frick Park, 14 July 2022 (photo by Charity Kheshgi)
Two juvenile Cooper’s hawks near their former nest in Frick Park, 14 July 2022 (photo by Charity Kheshgi)

July 14th was the last time we saw all six family members together. Five days later they had dispersed. The Cooper’s hawk family had grown up.

(photos by Charity Kheshgi)