Enemies spotting flying characters

Question

Are there any specific rules for enemies spotting flying characters? Or does anyone have any house rules they've used which have worked well?

One of my players has an aarakocra ranger, and he sometimes flies ahead as a scout. If he suspects there's enemies ahead, he flies past them, not obviously circling over them etc.

A stealth check doesn't quite feel appropriate here, as he's not trying to 'hide', and indeed he can't hide against the sky.

However, there's no specific reason a bunch of goblins who aren't expecting a flying player character would:

• be alert to check the sky, in order to even see him;
• realise they're seeing an aarakocra at 120' instead of a smaller bird at 60'
• and then realise an overflying aarakocra is scouting them rather than just generally flying past, and so either shoot at him, or prepare for a ground attack.

To be clear, I'm not looking for a way to "clip his wings"; I'm fine with having a flying character. I'm just looking for a sensible and consistent way to determine if enemies will spot him, and shoot and/or prepare. So far I've been rolling perception checks for enemies based on whatever arbitrary DC I pick that session, and the player hasn't been rolling anything.

Secondly, in the situation where enemies are forewarned to be alert for a flying character, what rolls might be appropriate? In this situation it's really just down to if they spot him. But again, rolling a stealth check doesn't seem relevant; he can't hide in the sky. If it were on ground, players walking past an enemy would always be spotted, but should they simply spot a flyer automatically?

If there's something in RAW which I can use, that's ideal, otherwise any house-rules which provide a balanced and consistent mechanism are fine. If there's something similar to a stealth check which a player can have some agency in rolling, that may be nice for the player, but that's not essential.

Answer 1

In this case, perception checks (or Passive Perception) with a set DC for the goblins would be appropriate.

Spotting things that are non-trivial to notice but aren't actively trying to hide is a Wisdom (Perception) v. DC skill check.

Your Wisdom (Perception) check lets you spot, hear, or otherwise detect the presence of something. It measures your general awareness of your surroundings and the keenness of your senses. [...] you might try to spot things that are obscured or easy to miss.

https://www.dndbeyond.com/sources/phb/using-ability-scores#Wisdom

It’s [The DM's] job to establish the Difficulty Class for an ability check or a saving throw when a rule or an adventure doesn’t give you one. Sometimes you’ll even want to change such established DCs. When you do so, think of how difficult a task is and then pick the associated DC from the Typical DCs table.

https://www.dndbeyond.com/sources/dmg/running-the-game#UsingAbilityScores

So, set a DC based on how hard you think it'd be for the monster to See the character, then perhaps a harder DC based on how hard you think it'd be for the monster to recognize the humanoid shape/judge the distance.

As to your concern about whether or not goblins would be watching the skies...

Keep in mind that these goblins live in a world inhabited by giant birds of prey, griffons, manticores, wyverns, and all manner of other flying things that might attack/eat a goblin.

For humans on Earth, we're really bad at watching the sky for threats because there is usually no reason to. There are no natural flying things that pose a persistent threat to our wellbeing. But if you lived in a world where a Giant Eagle might decide you looked like food--you'd likely be more attentive to the sky and what's in it.

Given that, the ability to watch the sky and to recognize what you're looking at (is that a normal Eagle at 60', or a Giant Eagle that might eat me at 120') is a valuable survival skill.

Answer 2

Stealth isn't just about taking the Hide action:

Stealth

Make a Dexterity (Stealth) check when you attempt to conceal yourself from enemies, slink past guards, slip away without being noticed, or sneak up on someone without being seen or heard. (PHB, Chapter 7, Dexterity Checks, Stealth)

1. Hiding generally requires Stealth rolls, but not all Stealth rolls are strictly for hiding. Any time a character wants to avoid being seen or attracting notice is a situation where a Stealth roll may be appropriate, even if the environment is not especially favorable for it. Situational adjustments might help give more context to the roll, like granting Advantage or Disadvantage, or adding flat bonuses or penalties to the roll.

   You're already describing the Aarakocra's efforts as ones where a Stealth roll may be appropriate, such as "flying past them" and "not obviously circling". If the player wants their character to deliberately try to avoid notice, a Stealth check is the way to determine how successful the character is at doing that. It's easier to say "I'm behaving casually and no one will notice me" than it is to do that. The character may be flying too low to be confused with an ordinary bird, or might not be able to give the impression of a casual fly-by, or might be flying over a goblin that happens to be a birdwatching expert, or a thousand other possibilities.

   It's not always reasonable for players to assert successs. A player can't necessarily declare that their character has successfully picked a lock or persuaded an NPC, and trying to do so might prompt the DM to call for a skill check. This is no different-- a desire for an outcome, and a reasonable plan to achieve it, may not be enough to guarantee success. As always, it's at the DM's discretion if a roll is necessary, but it's not obviously unnecessary in this situation.

2. You can totally be stealthy in the sky, though it may be a harder environment. For example, an Aarakocra flying so that it is between the sun and the are it is trying to observe would make it harder to spot. Other options include using cloud cover (if available), camouflage to be harder to see from the ground, and flight paths that make it hard to distinguish the Aarakocra from ordinary, non-threatening fliers. Stealth isn't the only potential skill to use, but it's definitely on the menu. Try telling an owl or peregrine falcon that stealthy flying is impossible!

   This is mostly narrative, and especially so if you're using a skill check. If a roll is called for, and the result is good enough, the character has found some way to succeed (even by plain luck).

3. Things in the sky can't spend all of their time at ideal angles to specific points on the ground. Even though a flying character might be out of view while directly overhead, they have to travel to that position from somewhere and might be visible while moving. You can easily see an airplane without looking up very much unless it's really high off the ground. There are a lot of ways to handle the approach and exit from the area, but a Stealth check could be a good choice for how the character handles those phases of their scouting missions.

4. Residents of most D&D settings may do poorly if they only look for a list of obviously suspicious things they expect to see, especially those that live beyond an established settlement. If the players encounter a band of goblins, there is at least a chance that they will be competent enough to appreciate a potential threat. And more organized groups may have more than a chance-- if it's an encampment of Hobgoblins, it might be reasonable for them to be very cautious when on watch.

5. Strategies shouldn't necessarily work flawlessly, all the time. With a flying character, I think that it's a good idea to let that character get some nice benefits from what is often a unique contribution to a party. But there is no reason that needs to continue forever. As the party's renown grows, word of the flying member may get around and make all enemies watch the sky a bit more carefully. Or an encampment might have a standing policy of shooting down all birds (even ordinary birds can be problematic with spells like Beast Sense and Talk with Animals available).

   The exact reasons and mechanisms that stop plans from working flawlessly and all the time can, and should, be flexible, and don't need to be applied in every instance. But the chance of failure is a huge part of D&D.

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What rolls?

There are a couple of overarching situations that may come up:

• If the potential observers are not actively trying to observe anything, then their passive senses may be most appropriate (especially passive Perception and passive Insight). You would set the passive score against the flying character's Stealth roll (if they make one), or a static DC reflecting how easy you feel the situation would make spotting the flier.
• If the potential observers are actively trying to observe things, then a Perception check is a natural choice to see if they notice anything at all. If they do notice anything (with or without a roll), rolls like Nature, Insight, or Investigation checks may be good choices for determining if they gain useful information about the nature of what they've seen.