As the Amazon book description has it:
My “ornithological treatise” Bad Birder’s Birding Report is actually illustrated nonsense verse in the tradition of Edward Lear, Lewis Carroll, Gillette Burgess, and Dr. Seuss. Featuring 125 poems and 130 illustrations, it mentions more than 150 species of birds, including virtually all of the most common North American species as well as several”exotics,” a few of which may not actually exist. The poems are alternately humorous, ironic, tragicomic, mystical and just plain nonsensical.
One of the mystically exotic species that “may not actually exist” is the Simurgh. Some readers no doubt wonder: “Where the finely feathered tarnation did this bird fly in from?!”
Short answer:
In منطق الطير The Conference of the Birds (alternately, The Logic of the Birds or Bird-Logic) by Attar of Nishapur, the Simurgh is a metaphor for the Divine. A flock of thirty birds (si morgh) journeys through seven perilous valleys to find their king, only to realize upon arrival that they collectively are the Simurgh, symbolizing unity with God and the reflection of truth within oneself.
I included a nonsensical nod to Attar and his English translator Fitzgerald in Bad Birder’s Birding Report:


Excerpt from Bird-Parliament (The Conference of the Birds)
Translated by Edward FitzGerald* (1889)
Then cried the Sun of Grace, “Oh, look not up,
Nor look without; but downward into the Cup
Of your own Hearts; for inside you shall see
The Only Mirror of My Majesty.”
They looked, and down into the Water stared:
And lo! the Thirty Birds themselves appeared
Reflected! And again they looked Above,
And saw the Simurgh on His Throne of Love!
And back and forth, from Throne to Water, eyes
Turned, wondering at the marvelous surprise.
They saw themselves the Simurgh here Below,
They saw the Simurgh themselves Above also;
And both were One, and One was Both—no trace
Of “I” or “Thou” remaining in that place.
A voice then spoke: “You came as Thirty Birds,
And Thirty Birds you see in these My words.
Had forty come, or fifty, you had seen
But forty or but fifty here convene.
For I am as a Mirror to your eyes:
Whatever enters, therein multiplies.
The Journey you have taken was from Me,
And to Yourselves you returned finally.
Annihilate your Selves, and you shall find
Immortal Life within the Divine Mind.”
And as they listened to the Simurgh’s voice,
They did in holy ecstasy rejoice.
The substance of their being was undone,
And they were lost like shade before the sun;
Neither the pilgrims nor their guide remained—
The Simurgh ceased to speak, and silence reigned.
*The translator of The Rubaiyat of Omar Khayyam, who famously said that all of his relatives were mad, and that he was insane as well, but was at least aware of the fact.
