Terror Bird (CR 4)

Large Animal
Alignment: Always neutral
Initiative: +7 (+3 Dex, +4 Improved Initiative); Senses: low-light vision, Listen +4, and Spot +4

AC: 17 (-1 size, +3 Dex, +5 natural), touch 12, flat-footed 14
Hit Dice: 7d8+21 (52 hp)
Fort +7, Ref +8, Will +4
Speed: 50 ft.
Space: 10 ft./10 ft.
Base Attack +5; Grapple +13
Attack: Bite +8 melee
Full Attack: Bite +8 melee
Damage: Bite 1d8+6
Special Attacks/Actions: Improved grab
Abilities: Str 19, Dex 17, Con 15, Int 2, Wis 14, Cha 10
Special Qualities:
Feats: Alertness; Improved Initiative; Skill Focus (Hide)
Skills: Hide +8, Listen +4, Move Silently +7, and Spot +4
Advancement: 8-14 HD (Large); 15-21 HD (Huge)
Climate/Terrain: Any forest, hill, or plains
Organization: Solitary or pack (3-6)
Treasure/Possessions: -

Source: Fiend Folio

Improved Grab (Ex): If a terror bird hits an opponent that is at least two size categories smaller than itself with a bite attack, it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity (grapple bonus +13). If it gets a hold, it automatically deals bite damage with a successful grapple check. A terror bird can move while maintaining the hold.

Terror bird packs try to encircle their chosen victims. When their prey seems least aware, flanking terror birds run in to distract the creature or creatures, while the leader runs in and attempts to grab a Small or smaller creature before running off to the pack's nesting ground. The others then cover for the fleeing, burdened leader. They know that if one returns with food, the rest of the pack will receive a share.