Watcher of the Spheres

Flying
Creature spells with flying you cast cost {1} less to cast.
Whenever another creature you control with flying enters, Watcher of the Spheres gets +1/+1 until end of turn.

Thrummingbird

Flying
Whenever Thrummingbird deals combat damage to a player, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Gravitational Shift

Creatures with flying get +2/+0.
Creatures without flying get -2/-0.

Gitaxian Raptor

Flying
Gitaxian Raptor enters with three oil counters on it.
Remove an oil counter from Gitaxian Raptor: Gitaxian Raptor gets +1/-1 until end of turn.

Cartographer's Hawk

Flying
When Cartographer's Hawk deals combat damage to a player who controls more lands than you, return it to its owner's hand. If you do, you may search your library for a Plains card, put it onto the battlefield tapped, then shuffle.

Plumecreed Escort

Flash
Flying
When Plumecreed Escort enters, target creature you control gains hexproof until end of turn.

Plumecreed Mentor

Flying
Whenever Plumecreed Mentor or another creature you control with flying enters, put a +1/+1 counter on target creature you control without flying.

Finch Formation

Offspring {3} (You may pay an additional {3} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
Flying
When this creature enters, target creature you control gains flying until end of turn.

Mockingbird

Flying
You may have Mockingbird enter as a copy of any creature on the battlefield with mana value less than or equal to the amount of mana spent to cast Mockingbird, except it's a Bird in addition to its other types and it has flying.

Warden of Evos Isle

Flying
Creature spells with flying you cast cost {1} less to cast.

Monastery Flock

Defender, flying
Morph {U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Gwaihir, Greatest of the Eagles

Flying
Whenever Gwaihir attacks, target attacking creature gains flying until end of turn.
At the beginning of each end step, if you gained 3 or more life this turn, create a 3/3 white Bird creature token with flying and "Whenever this creature attacks, target attacking creature gains flying until end of turn."

Empyrean Eagle

Flying
Other creatures you control with flying get +1/+1.

Jackdaw Savior

Flying
Whenever Jackdaw Savior or another creature you control with flying dies, return another target creature card with lesser mana value from your graveyard to the battlefield.

Knightfisher

Flying
Whenever another nontoken Bird you control enters, create a 1/1 blue Fish creature token.

Dazzling Denial

Counter target spell unless its controller pays {2}. If you control a Bird, counter that spell unless its controller pays {4} instead.

Flensing Raptor

Flying
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)
When Flensing Raptor enters, another target creature you control with toxic gets +1/+1 and gains flying until end of turn.

Kastral, the Windcrested

Flying
Whenever one or more Birds you control deal combat damage to a player, choose one —
• You may put a Bird creature card from your hand or graveyard onto the battlefield with a finality counter on it.
• Put a +1/+1 counter on each Bird you control.
• Draw a card.

Dawnfeather Eagle

Flying
When Dawnfeather Eagle enters, creatures you control get +1/+1 and gain vigilance until end of turn.

Eddytrail Hawk

Flying
When Eddytrail Hawk enters, you get {E}{E} (two energy counters).
Whenever Eddytrail Hawk attacks, you may pay {E}. If you do, another target attacking creature gains flying until end of turn.

True Conviction

Creatures you control have double strike and lifelink.

Dire Downdraft

This spell costs {1} less to cast if it targets an attacking or tapped creature.
Target creature's owner puts it on their choice of the top or bottom of their library.

Migratory Route

Create four 1/1 white Bird creature tokens with flying.
Basic landcycling {2} ({2}, Discard this card: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.)

Strix Lookout

Flying, vigilance (Attacking doesn't cause this creature to tap.)
{1}{U}, {T}: Draw a card, then discard a card.

Favorable Winds

Creatures you control with flying get +1/+1.

Seedpod Squire

Flying
Whenever Seedpod Squire attacks, target creature you control without flying gets +1/+1 until end of turn.

Brave the Sands

Creatures you control have vigilance.
Each creature you control can block an additional creature each combat.

Scouting Hawk

Flying
Keen Sight — When Scouting Hawk enters, if an opponent controls more lands than you, search your library for a basic Plains card, put it onto the battlefield tapped, then shuffle.

Soulcatcher

Flying
Whenever a creature with flying dies, put a +1/+1 counter on Soulcatcher.