In an earlier article, we referred to the importance of establishing a baseline for your campaign world so that you provide a background of normalcy against which the strange and supernatural happenings of a typical D&D campaign can take place. Encounters and campaign situations need not be repetitious or boring, but if everything is always different, that sense of difference, uniqueness, and magic that you gain from introducing new things can be lost. In the interest of providing a specific and concrete example of how this can be implemented in a campaign, I suggest that you should do as Dr. Doolittle did and think about the animals.
In the real world, animals comprise a vital and common part of the ecology that we encounter every day, and the particular variety of animals is characteristic of different lands, regions, and terrain types. You can discern a region's character by looking at the animals that inhabit it, and that gives depth to the region and makes it memorable. In D&D, monsters of various sorts fill that role, but only to an extent. In D&D, you have monsters and animals, and you cannot ignore one at the expense of the other. If the native wildlife consists of ogres, hell hounds, monstrous spiders, drow elves, werewolves, and merchants, the players may start to wonder what everyone eats or what they hunt. You don't need to put chipmunks and ducks on the encounter tables, but larger herbivores are certainly reasonable candidates to appear as random encounters. Not every encounter need be hostile in the case of sentient beings (for example, militia patrols, merchant parties, and so on), and the same should apply to nonsentient beings. If the characters decide to stir up trouble by messing around with an irascible moose, boar, swan, or wild horse, they may find more trouble than they expected in the bargain, though most such creatures will happily ignore them if not molested. The simple fact that encountering them is reasonably likely helps ground the fantasy world in a sense of realism in a way very much like incorporating weather, seasons, holidays, and the like can do: It makes the background come alive.
However, the animals in your fantasy world don't necessarily have to act exactly like their counterparts in the real world. The recent TV miniseries Dinotopia evoked criticism from some by referring to "herds" of tyrannosaurs and "swarms" of carnivorous pteranodons, since paleontology suggests that on our world there never were any such things. Well, Dinotopia is based on a fantasy world, and apparently in that world there are herds of tyrannosaurs and swarms of carnivorous pteranodons! The same could apply to animals in your D&D campaign: Maybe your wolves are solitary and perhaps sentient (or able to converse telepathically or in dreams, as in Robert Jordan's Wheel of Time series), or perhaps mountain lions hunt in packs. Such changes in behavior patterns are certainly fair enough tweaks in a fantasy game. At the same time, you don't want to make them too different, or else you just end up creating a new kind of unnatural monster. That may be a cool monster idea, like the flesh-eating mares of Diomedes or any of the other monstrous animals that were the subject of one of Heracles' labors, but at that point you have crossed the line from animal to monster and ended up defeating the main point of using animals in your campaign, which is to give it a veneer of naturalistic realism. You don't need to create a nature documentary about the animals in your world (though you might get interesting ideas for animal encounters from watching networks like Discovery or Animal Planet), and you really need not obsess over the minutiae of habitat and ecology. A basic rationale for the "natural" wildlife of a given area is all that you really need and it sets the context for how other creatures interact with and exist within that environment. Animals are not really the stars of the show in terms of adversaries for the characters in D&D; they are more like solid supporting players, and running them more or less "as is" is usually the best way to go.
As for how to use animals intentionally in encounters, over and above their presence in the background, you should be careful to use their natural cunning (if any) without going overboard to making them super-intelligent. In the late 1980's, Dragon Magazine published an article describing a wide variety of dangerous animals, not all of which were carnivores, including some of the tactics used by real-world animals in hunting or aggressive defense. Those lacking the CD-ROM Dragon Archive or an extensive back issue collection can certainly find similar information in animal-related magazines, websites, or channels such as Animal Planet or the Discovery Channel. Looking at the behavior of real-world animals can give you a sense of how to realistically portray aggressive or dangerous animal behavior, even if you transplant one animal's tactics or habits onto an entirely different animal.
The core of the issue is to "get into the mind of the animal" so that you can convey an animalistic nature that separates it from being just another monster. It likely is not bothering the party because it is inherently malicious, but because it is following a more primal motivation -- hunger, protection of territory, protection of home or young, or even fear. The way it behaves can be derived from its motivations, and its tactics will fit the situation. An animal that attacks from hunger will likely attack a mount or pack animal, or perhaps a small party member, trying to kill it as quickly as possible. If it cannot carry off the remains at once, it might just hope the party leaves the carcass there for it to feast on later. If in desperate hunger, it might try to guard the kill if the party returns, fearful of them stealing its food. If an animal is defending its territory, it will most likely watch the party from hiding, hoping they will leave on their own, or try to scare the party off with roars and growls.
You can also supplement basic tactics with feats and abilities that seem appropriate to the combat methods used by animals. For some animals, such as those trying to scare another creature away from their territory, attacks will be quick and are followed by a swift retreat. You might reasonably grant certain animals an ability that essentially grants them the Spring Attack feat (with or without also granting them Dodge and/or Mobility) if you judge that this is a standard tactic for that animal. Animals defending their young may first try to scare off intruders and then retreat into whatever den or shelter is available and then attack with great ferocity (perhaps the equivalent of a barbarian's rage ability) if interlopers press on. (Also take a look at the pounce ability that a lion has on page 198 of the Monster Manual.) Pack attackers like wolves or jackals might gain an ability that mimics the Dual Strike feat from Sword & Fist to represent their familiarity with flanking tactics. The application of such extras to animals can bring out their particular strengths, but they also may make such animals more dangerous in combat, so you should consider adjusting XP awards for defeating such creatures in light of their added abilities.
A final reason to incorporate animals as a regular feature of your games is that it reinforces the raison d'etre of a large number of classes, skills, feats, spells, and magic items in the game. If the party rarely meets animals, no one may bother spending skill ranks on Animal Empathy or Handle Animal (unless they want the +2 synergy bonus to Ride checks) or prepare speak with animals or even bother taking levels in druid or ranger (or animal-related prestige classes). At the same time, a character who has devoted skills, feats, spells, or class levels in areas related to animals may feel they have gotten the shaft, because a bunch of their abilities may never come into play. Think of the player of a cleric in a world with no undead or a rogue in a world where the majority of encounters are immune to criticals (and therefore sneak attacks). Are there other things the character can still do? Sure, but at the same time a significant part of their character's investment in what he or she can do has been invalidated, or at least constrained, by the absence of animals as a regular feature of the campaign world. A game where animals are just an invisible part of the background unless they get summoned by a spell has a similar effect on nature-based elements of the game. They don't become useless, but they are certainly less useful.
Looking at the other side of the same coin, animals present unique and different challenges to character classes that do not include skills that can handle them. Low-level spells that affect only "persons" are of no use against them, and they can frequently circumvent defensive magic with abilities like Scent (or simply having high Spot and Listen scores). Animals often enjoy a tactical movement advantage over characters, in addition to an array of special attack forms (like rend, trip, improved grab, and poison) that can spell big trouble for characters. Using animals on regular basis forces characters to come to grips with the breadth of wildlife in their world and to be prepared for the fact that animals are a part of life. Those who choose to prepare their characters or their parties to deal with animals, whether hostile or not, often have an easy time circumventing possible danger. Those who ignore animals do so at their peril since their characters will end up having a rougher go of it.
Making regular use of animals as part of your campaign does not force players to play naturalist classes, but it does present them with a full palette of options and allow them to make their own choices. As the rules are written, animals are one of those choices, but as campaigns play out, they frequently fade into irrelevance. D&D is all about setting priorities and making choices, and using animals as a regular part of your game restores the legitimacy of those choices. Including animals in your encounter generation system helps remind you as the DM to maintain a sense of the natural in the nature of your world. This in turn helps your players see the world and its environment as natural and believable, lets the supernatural elements of your D&D world stand out as special, and makes everything a little more memorable.
 You might apply an ad hoc XP penalty (see the Dungeon Master's Guide, page 167) for encounters that pose little real risk to the party, including those that include little or no risk unless deliberately provoked by the party.
About the Author
Jason Nelson lives in Seattle and is a full-time homemaker (taking care of his 7-year-old daughter, 4-year-old son, and new dog), a part-time graduate student (working on a Ph.D. in education policy), and an active and committed born-again Christian. He runs a weekly D&D game, having just completed a seven-year-long AD&D (heavily modified) campaign set in the Forgotten Realms. He began playing D&D in 1981, and he also plays in a biweekly campaign with a D&D version of his very first character (Tjaden Ludendorff, a psionic paladin) from 21 years ago!
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