The Kiesha'ra by Amelia Atwater-Rhodes is a five book, young adult fantasy series about the war between avian and serpiente shapeshifters. Each book has a different narrator; other kinds of shapeshifters become important in the series as well. It takes place a few thousand years before the events of the Den of Shadows series.
Hawksong - The first book, narrated by Danica Shardae, shows the age-old war the avians and serpents are fighting. Danica, the heir to the avian throne, wishes to work out a peaceful end to the war with Zane Cobriana, the next in line to rule the serpents, but their solution - getting married - may be too much for them to sacrifice and their people to handle.
Snakecharm - Zane narrates the search for a criminal falcon shapeshifter while he and Danica try to keep the new peace and keep Danica alive and well during her pregnancy. Falcon shapeshifters begin to come into the spotlight.
Falcondance - A twenty year Time Skip leaves the narration in the hands of falcon Nicias Silvermead, elite guard of Oliza Shardae Cobriana, Zane and Danica's daughter. He develops falcon magic even though his parents' magic is bound and is forced to go to the falcon island of Ahnmik, where he is royalty and nothing is as it seems.
Wolfcry - Oliza picks up the narration as she tries to find a mate without destroying the fragile peace between the avians and serpiente - before being kidnapped. Most of the book is her struggle to return home after being carried to the far north, into an unfamiliar wolf shapeshifter tribe's territory, as well as her struggles to figure out how to keep her people united when she takes the throne.
Wyvernhail - The last book is narrated by Hai, a falcon/cobra shapeshifter. She tries to define where her loyalties lie while trying to keep avian and serpiente society from crumbling.
Ancient Conspiracy: Hundreds of years ago, in order to stop the falcon-serpiente war, falcon priestesses Araceli and Cjarsa ripped out half of cobra leader Kiesha's magic, put it into a human child, and essentially created the avian races. Later, they instigated the war between the avians and serpiente so that the two species would never join together again, disrupt the balance of magical power and possibly destroy the world.
Arranged Marriage: Avian children are betrothed nearly at birth. The engagement can be broken in the future, though.
Bodyguard Betrayal: Darien rebelled against Empress Cjarsa when she found out that Cjarsa and Araceli had started the avian-serpiente war. She doesn't succeed, though.
Bodyguard Crush: Adelina towards Zane, Andreios towards Danica, Nicias towards Oliza...
Broken Bird: Hai. Literally, what with her broken wings.
Cannot Tell a Lie / Language Of Truth: Falcon magic prevents falcons from breaking oaths and telling outright lies without disastrous consequences. Their culture has thus mastered the art of manipulation.
Can't Have Sex, Ever: Oliza and other halfbreeds - but it's more like Can't Have Babies, Ever. (This is handily solved when Oliza chooses Betia, another female, as her mate.) See Enfant Terrible below.
Culture Clash: Best seen between the avians and serpiente, oh so very much.
Cycle of Revenge: What keeps the avian-serpiente war going for hundreds of years.
Dead Person Impersonation: Sebastian the falcon prince takes on the original Andreios' likeness in an attempt to heal him and ends up pretending to be Rei for the next few years. Same with Kel, who pretends to be the deceased Erica Silvermead.
Dark Is Not Evil: The cobras are fairly nice once you get to know them, even if Zane does enjoy wearing black snakeskin pants.
Also Nicias, who has no interest in becoming the ruler of Ahnmik.
Immortality Begins at Twenty: All shapeshifters age like humans until their twenties, then stop aging. The avians and serpiente keep killing each other off before anyone reaches a significant age, though.
Interspecies Romance: Danica and Zane. Ones that lead to children are discouraged among falcons because falcon blood mixed with other blood usually leads to destructive magic that's difficult to control, though they're fine if no children come from the union.
Not to mention Oliza and Betia.
Also Hai's parents.
I Want My Beloved to Be Happy: Adelina says something along this line to Danica regarding Zane, before announcing her plans to resign from the palace guard. Kind of subverted, as it doesn't stop her from trying to kill Danica later that night, and consequently killing Zane's mother instead.
Played straight with Rei and Danica.
Light Is Not Good: Sure, Ahnmik (aka. the White City) might look nice and angelic...unless you piss off the royals/find out something you really shouldn't know/are mixed blood of any kind.
Magic Dance: Both the falcons and the serpiente had the ability to work magic through dance. The serpiente lost the ability thousands of years ago, but for falcons, dance magic is some of the most powerful and most difficult to work.
Magic Genetics: According to Word of God, what kind of shapeshifter a child is depends on which parent's species is 'dominant' over the other. Some are codominant, like hawks and cobras, resulting in wyverns like Oliza. Add falcon magic into the mix and procreation becomes one huge jumbled headache.
Manipulative Bastard: Darien, Araceli, Cjarsa, Syfka...let's just go with the entire population of Ahnmik, shall we?
Marriage Before Romance: It's a political match — their peoples have been at war for generations, they're the royal heirs, and they decide that they can make peace via a marriage alliance. It works, and they fall in love later.
Marry for Love: To the serpiente, marriages should ALWAYS be like this - which is why Zane and Danica have to pretend to be in love in front of Zane's people.
Memetic Badass: In-universe example; Zane's prowess on the battlefield is exaggerated and feared by the avians.
Mixed Ancestry: Oliza and Hai are both wyverns; Oliza is half hawk, Hai is half falcon, and both are half cobra. Instead of the usual three forms, they have five.
Multicolored Hair: Falcons are all blonde with blue or violet streaks in their hair, indicating their magical power. Oliza has black hair with red highlights.
Not So Different: Zane's speech to Nacola Shardae, Danica's mother, about their two species:
Zane: The first of my kind was a human woman. Surely your kind comes from like roots. We have human minds and human bodies. If we can speak as humans do, and love as humans do, then what makes us so different?
Parental Marriage Veto: Danica and Zane's parents are NOT happy when their children decide to get married to end the war between their races. Not that they can do anything about it, since their children are now the monarchs.
Red Eyes, Take Warning: Subverted; red eyes are simply a trait of the Cobriana bloodline. It does freak Danica out in the beginning though.
Royals Who Actually Do Something: Pretty much all of them, fortunately. Activities include leading the troops into battle, mingling among the citizens, active decision-making, and manipulating the tides of politics in one's favor. Et cetera.
[[Seers Seers]]: Powerful falcons and Oliza, with assistance have clairvoyant and precognitive abilities.
Shapeshifter Mode Lock: Punishments for high crimes are talked about, though never shown; for both serpiente and avians, they involve taking away the full animal and Demi forms (through skinning or wing shearing) before either exile or death. On Ahnmik, certain classes of falcons are not allowed to shift into animal forms. Injuries can also stop shifting; Hai can't shift into a falcon because her wings are broken. And in Wolfcry, Oliza is poisoned and loses her hawk form for most of the book.
Shoot the Shaggy Dog: Hawksong is all about how Danica and Zane can love each other despite their radically different backgrounds. Snakecharm is all about combining the avian and serpentine cultures into one breathtakingly beautiful city. Wolfcry ends with the heir to both cultures deciding that it won't work out, and splitting them into two again. This is especially frustrating for 11-14 year olds reading it soon after Snakecharm. When you're young and idealistic and loved the first two books, the fourth one is kind of a downer.
Snakes Are Sexy: The serpiente certainly have a more sexually open culture.
Succession Crisis: Occurs in Wyvernhail after Oliza abdicates her right as heir to the avian and serpiente thrones. To elaborate, Oliza's father Zane then abdicates the serpiente throne to her cousin Salem, who gets poisoned and falls into a coma, forcing Oliza to come back as the new ruler again, forcing her other cousin Hai to "usurp" the throne to prevent the horrible future she saw in her visions. Confused yet?
Super Power Meltdown: What happened to Hai that burned her wings, and what could happen to other half-breed falcons since they have problems controlling their magic.
That Was Not A Dream: Danica dreams that Zane visited her at night to give her his ring and arrange a meeting at his palace. She wakes up and goes about business as usual. Then she finds the ring under her bed. Cue realization that she's days late for a meeting that might decide the fate of her entire country.
Time Skip: The series skips twenty years between Snakecharm and Falcondance. The shift is not only in time; Falcondance, Wolfcry, and Wyvernhail shift the action from Hawk's Keep and the serpiente palace to Wyvern's Court and Ahnmik.
Voluntary Shapeshifting: Each shapeshifter in the series has three forms: a full human form, a full animal form, and a Demi form that is mostly human with some animal traits (for example, bird shapeshifters get wings and a lighter bone structure). Shapeshifters are confined to one animal, determined by their bloodline. Kinds seen in the series include:
Avians: Bird shifters; golden hawks, ravens, crows, and sparrows
Serpiente: snakes; cobras, emerald boas, pythons, vipers, black rats, red rats, taipans, and mambas
Obsidian: white vipers, once part of the serpiente
Shm'Ahnmik: Falcons; peregrines, merlins, aplomados, and gyrfalcons
Mistari: Tigers and goshawks
War Is Hell: Played interestingly in Hawksong; this trope is definitely a theme, but instead of focusing on how bad war is, it focuses on how good peace is.