Putting together the diet of the Great Blue Heron

My daughter loves dissecting owl pellets. When we found a large accumulation of great blue heron guano on our property, she was excited at the prospect of dissecting it. We put on some gloves and put the pellets in a set of seives with the hopes of extracting the mineralized remains of the bird's diet. Unanticipated was the massive amount of fir and feathers, which blocked the seive and generally reduced the efficacy of the process.

The great blue heron is a very versatile bird. I have only really known it as a shore bird, but it lives and hunts almost everywhere. And it doesn't neccesarily just hunt. My birding guides refer to it as an opportunistic omnivore. That means anything, anytime when the item suits it. This particular bird nest in a Douglas fir in the area, retreating to this open shed when it gets really wet and stormy. It could be feeding in ditches, ponds, tidepools, shorelines and other places beyond my imagination. At least that seems to be the case based on what we found. Bones up to about 1.25 " made up the corpus of the frass. See the associated observations of rodents, fish, egg shells, birds, crabs, dead pinnipeds and seeds. We also found a number of ~5mm well polished stones. These could have been bycatch, but maybe they were gastroliths-- the rocks and pebbles kepts in the guts of dinosaurs and birds to help mechnically break down their food. The heron, like many of its dinosaur ancestors, is a gulp and go eater. It does not chew the food so much as swallow it whole. The stones in the gut break these food items down. Would be interested in hearing from any bird people who have thoughts on what some of these prey items might be, particularly the rodent. @jamie_fenneman @jbindernagel

Posted on March 18, 2020 08:17 PM by rambryum rambryum

Observations

Photos / Sounds

What

Great Blue Heron (Ardea herodias)

Observer

rambryum

Date

March 18, 2020 10:32 AM PDT

Description

Accumulation of guano under roofed area. Note egg shells, gastroliths

Photos / Sounds

What

Grasses (Family Poaceae)

Observer

rambryum

Date

March 18, 2020 11:19 AM PDT

Description

In guano of great blue heron

Birds

Photos / Sounds

What

Birds (Class Aves)

Observer

rambryum

Date

March 18, 2020 11:19 AM PDT

Description

Shell fragments in guano of great blue heron

Photos / Sounds

What

Dicots (Class Magnoliopsida)

Observer

rambryum

Date

March 18, 2020 11:20 AM PDT

Description

Seed (Chenopodiaceae?) in the guano of great blue heron

Mammals

Photos / Sounds

What

Mammals (Class Mammalia)

Observer

rambryum

Date

March 18, 2020 11:20 AM PDT

Description

chunk of decaying hairy flesh with the stink of a dead sea lion or seal. From guano of a great blue heron

Birds

Photos / Sounds

What

Birds (Class Aves)

Observer

rambryum

Date

March 18, 2020 11:20 AM PDT

Description

Feathers in guano of great blue heron

Photos / Sounds

What

Rodents (Order Rodentia)

Observer

rambryum

Date

March 18, 2020 11:20 AM PDT

Description

Rata? Squirrel? Mouse? Vole? Jaw from the guano of a great blue heron

Photos / Sounds

What

True Crabs (Infraorder Brachyura)

Observer

rambryum

Date

March 18, 2020 11:21 AM PDT

Description

Carapace fragmment from guano of great blue heron

Photos / Sounds

What

Salmons, Trouts, and Whitefishes (Family Salmonidae)

Observer

rambryum

Date

March 18, 2020 11:21 AM PDT

Description

1cm diameter frfom the guano of a great blue heron

Photos / Sounds

What

Dicots (Class Magnoliopsida)

Observer

rambryum

Date

March 18, 2020 11:22 AM PDT

Description

Seeds from the guano of a great blue heron. Polygonaceae?

Comments

Very cool. I watched a heron stalk rodents in a field along the base of a dike out by Stanwood. There are YouTube videos of herons gulping down ducks and other prey. They're rather terrifying birds.

Posted by brownsbay about 4 years ago

Herons certainly take rodents on a regular basis. I've seen them take grayish plump rofdents in fields, which I suspect are townsend's voles. Townsend's voles are probably a likely food source as they live in habitats where herons often forage (grassy fields and seasonally flooded areas). The other options on the island would be deermice, red squirrels, black and brown rats, and house mice. All of these species live in areas that are generally not frequented by hunting herons, so I'd suspect that that jawbone belongs to a townsend's vole, or perhaps a rat, as they seem less averse to living it wet fields than the other rodents mentioned. Hopefully somebody who konws mammal bones can confirm or refute the hypothesis that this is a vole jaw.

Posted by jbindernagel about 4 years ago

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