Monstrous Mondays: Thunderbird (and Basic Bestiary updates)

Work on Basic Bestiary has picked back up. I have 360 completed monsters for it now. I still have my next pass at editing and mechanics tweaking to complete.  What I really need is art. I don't have any, and while I am happy to use some PD art for it (and it fits the look I want), I will need more. A lot more. While I don't mind AI art (and appreciate the computer science that went into it), I can't in good conscience use any in this. 

Still playing around with stat block ideas. Since this is a "Basic" Bestiary, I figure I should get closer to the Basic-era stat block details as I can. I am adding some "modern" ideas like creature size and type (something we see in BECMI and RC, but not BX), and Ascending AC (Basic Fantasy, OSE and LL).  I need to decide if I want to include other details like Advanced era alignments (I am leaning towards yes), Languages (also yes), and Frequency. I am also still considering hp adjustment due to size. I like it a lot, and it makes creatures a lot tougher.

I believe I have settled on using BX/OSE style XP awards and having a table in the back for all the other games I think people might want to use this for, as long as they are OGC.  Edited: I noticed my math might be off on some higher HD monsters. 

The stat block below is what I am thinking so far. Love to hear some feedback on it.

Yes. I am still going to use the OGL for this one. I have gone too far down that road to go back.

Here is one of the last monsters I worked on for the book. As always, the final version might be different.

Thunder Bird
Gargantuan Beast (Magical)

Armor Class: -5 [24]
Hit Dice: 17d8+68 (145 hp)
   Gargantuan: 17d20+68 (264 hp)
Move: 90' (30')
   Flying: 360' (120')
Attacks: 2 claws, 1 bite, special
Damage: 1d12+5 x2, 2d8+5, special
Special: Lighting bolt, thunder, wing buffet
No. Appearing: 1 (1, or 1d4+1, mated pair with chicks)
Save As: Monster 17
Morale: 10 (12)
Treasure Type: None, See below
Alignment: Neutral (True Neutral)
XP: 6,600

Languages: Avian

Thunderbirds are gargantuan birds that appear as storm gray-colored eagles. They have a 70' wing span that can blot out the sun and talons that can carry off livestock, usually one or two cattle each. Their eyes flash with electrical light and can shoot lightning bolts. When their wings flap, they can cause storms and thunder. Natives of the lands the thunderbird calls home to revere the bird as a messenger of the forces of good and liken it to a spirit. It is a mortal animal, albeit a very powerful one. 

The thunderbird can attack with its massive beak and talons.  It swoops down from their mountain homes, which can be hundreds of miles away, to attack its prey. It prefers large cattle, like horses, cows, and bison, and can carry off up to 2,000 pounds worth at a time. Thunderbirds that live near oceans will even make a dinner out of whales when they can catch them. They do not attack humans if they can avoid it. They do not like the taste and attack humans since humans often return in greater numbers and with weapons. If attacked by humans on the ground, the thunderbird will often just opt to fly away. Thunderbirds and Rocs do not get along as they tend to go after the same prey. Their relationship is similar to that of eagles and hawks.  

The thunderbird gets its name from the magical storm-creation powers it has. By flapping its wings and remaining stationary, it can create a thunderclap that does 10d6 hp of damage; Breath Weapon saves for half the damage. Which will also define anyone within a 120' long cone, 60' at its widest.  Targets outside of the 120' are unaffected by either the damage or the deafness. It can also 3 times per day cast a 10d6 lighting bolt from its eyes. The range on this is 100', save vs. Breath Weapon for half damage. Ranges outside of 100' to 300' are at half-damage or save for no damage.  The thunderbird will not use this attack against food prey but rather to defend itself from humanoids or other large creatures it finds itself engaging with.  A thunderbird can also summon storms as per the Summon Weather spell. 

Thunderbirds have no need nor interest in treasure. The feathers of the thunderbird are highly prized as a main ingredient for a staff of lightning bolts and other magical staffs. Their feathers are also used in other magic item creations, typically Wings of Flying. Any item that requires a roc feather can use a thunderbird feather instead for a 50% increase in either speed or duration. The feathers of a thunderbird usually can bring in 1,000 gp on the right markets (usually only 2d6 are viable for arcane use). The eggs of thunderbirds are so rare to discover that bounties of 12,000 gp and more are sometimes offered. The lairs of the thunderbird are usually at the tops of mountains so high they are very nearly impossible to reach. 

Tales tell of a great thunderbird so large that when it flies, the land below is thrust into night. This could be a single unique specimen or an undiscovered variety.