CR help on some custom monsters

[powerdemon]

I'm looking for some help assigning a CR to this monster I made.

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Scavenger
Medium Animal
Hit Dice: 3d8+6 (19)
Initiative: +2
Speed: 50 ft. (10 Squares)
Armor Class: 15 (+2 Dex, +3 natural), touch 12, flat-footed 13
Base Attack/Grapple: +2/+5
Attack: Bite +6 melee (1d8+4)
Full Attack: Bite +6 melee (1d8+4)
Space/Reach: 5 ft./ 5 ft.
Special Attacks: Frenzied Charge
Special Qualities: Low-light Vision, Scent
Saves: Fort +4, Ref +5, Will -1
Abilities: Str 16, Dex 15, Con 12, Int 1, Wis 7, Cha 4
Skills: Listen +0, Spot +0, Survival +6
Feats: Weapon Focus (bite), Improved Natural Attack (bite)
Environment: Temperate hills and forests
Organization: Flock (4-10)
Challenge Rating: 2
Treasure: None
Alignment: Always Neutral
Advancement: 4-6 HD (Medium); 5-9 HD (Large)
Level Adjustment: -

Scavengers are medium sized flightless birds. They have two clawed legs and no arms. Their beaks are sharp and good for ripping apart whatever meal they have found as well as their foe.

Combat
Scavengers travel in packs and will attack in packs unless they are separated from the flock. If a scavenger notices a threat, it will crow at it to try and warn them away, then it will use their Frenzied Charge ability to try and kill the foe as fast as possible. Scavengers will fight to the death.
Frenzied Charge (Ex): When a scavenger charges an opponent, it can make three melee attacks at the end of the charge. The second attack is at a -3 penalty, and the third at a -6 penalty.
Skills: Scavengers are very oblivious to their surroundings and have very poor listen and spot skills.

Does the CR 2 seem good? I would do a 2.5 if that was possible, but as it is, it think it's more powerful than a 2, but less than a 3.

[powerdemon]

And this is the second one:

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Bloodfly
Small Vermin
Hit Dice: 5d8+5 (23)
Initiative: +4
Speed: Fly 30 ft. (6 Squares)
Armor Class: 20 (+1 size, +4 Dex, +5 natural), touch 15, flat-footed 16
Base Attack/Grapple: +3/+0
Attack: Sting +8 melee (1d6+1 plus wound)
Full Attack: Sting +8 melee (1d6+1 plus wound)
Space/Reach: 5 ft./ 5 ft.
Special Attacks: Bloody Sting
Special Qualities: Darkvision 60 ft.
Saves: Fort +5, Ref +8, Will +2
Abilities: Str 13, Dex 19, Con 12, Int -, Wis 12, Cha 6
Skills: -
Feats: Weapon Focus (Sting), Weapon Finesse
Environment: Temperate hills and forests
Organization: Swarm (3-8)
Challenge Rating: 3
Treasure: None
Alignment: Always Neutral
Advancement: 6-10 HD (Small)
Level Adjustment: -

Bloodflies are vicious flying insects that have very dangerous stingers attached to their tails. About the size of a Halfling, these insects are very dangerous, especially in groups.

Combat
Bloodflies attack anything that gets too close and always attack in groups if possible.
Bloody Sting (Ex): In addition to regular damage, anyone hit by a bloodfly’s tail sting is wounded and takes 1 hp of damage per round until they benefit from a healing spell that heals at least 1 hp of damage, or receive a successful heal check DC 15. This ability stacks up to three times on each victim.

[Debihuman]

The challenge rating is geared to challenge 4 party members. That's why you see 1/2 and sometimes 1/4 CRs. CR 1/4 basically means that a single party member at first level can take out the creature.

I think CR 2 is good for the scavenger. The bites with frenzied charge are way too nasty and lethal for CR 1 but they don't any defensive abilities. Their above average speed gives them a bit of an advantage but not enough. Really, this is a CR 1 monster that just does too much damage to justify pitting it against level 1 PCs.

The Bloodfly is a bit too weak for CR 4. This is not much harder to defeat than bat swarm, which is CR 2 and also has the wounding ability. CR 3 would make more sense.

Debby

[powerdemon]

First, thanks for the input :P

I originally had the frenzied charge with all three attacks at full attack bonus.... Then one killed a party member (with the highest AC) in one round :P

The bloodfly I am having a harder time with. The sting I thought would constitute a higher CR, but looking at it now, you're right.