What are the rules for switching an animal companion and how exactly are they summoned?

Question

I have a Druid and a Ranger in the game I'm DM'ing. They constantly change their animal companions. I know that a Druid can release an animal companion from service and get another one (or replace a dead one) for 24 hours of interrupted ritual. Is it the same for Ranger?

How does summoning happen exactly? Do the animals just pop into existence like a Summon Monster spell or does the Druid or the Ranger try to call an animal into their service with their rituals? Can they call any kind of animal regardless of the biome they are in? For example, can they get a camel in the woods, or can they get a wolf in a metropolis? Do they have to be in a biome where the animal could be found? It doesn't make any sense for them to be able to get a camel in the woods if they are not summoning the animal like a Summon Monster spell really.

When an animal companion dies, do they disappear like how a creature summoned by a Summon Monster would die, or do they die like a normal animal?

It would be great if I can get page numbers describing these rules.

Answer 1

The Ranger's entry for Animal Companions (page 48 of the Player's Handbook) specifically states

This ability functions like the druid ability of the same name, except that the ranger’s effective druid level is one-half his ranger level.

So Rangers also require 24 hours of uninterrupted time to replace a released or dead animal companion.

While there is nothing within the Player's Handbook regarding how the an animal companion is acquired, there is a section within Masters of the Wild that gives a more expansive set of rules on animal companions (page 34 onward). Please note though that Masters of the Wild is a 3e book, not 3.5, and as such certain elements of it have been superseded and other elements don't make a lot of sense (eg. the animal companion spell talked about in Masters of the Wild does not exist in 3.5), but it still does add a number of much more flavourful rules to a character's interaction with their companion.

As you surmise, the Animal Companion ability is not a magical effect - the animal does not simply "pop" into being like a summoned monster, the character must search within the typical terrain and climate that is home to the animal they are desiring. As such a dead animal companion would also leave a corpse like any other dead character within the party.

Masters of the Wild also requires a potentially greater amount of time to find an animal, saying that with a successful Wilderness Lore check to determine the animal's native terrain and climate and with the use of the detect animals or plants spell, that the character has a 30% chance per day of finding an animal of the desired type. While this is a much more flavourful rule for finding an animal companion, I can also understand why 3.5 has made this a flat 24 hour period without the need for spells or skills.

Masters of the Wild also expands on the bond between the PC and the animal, stating that it is a friend, not a slave, and it may grow tired of ill-treatment or constant damage-taking in fights. While the animal starts with an attitude of helpful, the GM should adjust the animal's attitude on the NPC Attitude table on page 149 of the Dungeon Master's Guide due to neglect or abuse, and that an animal that becomes hostile or unfriendly will do its best to leave the PC.

One further thing that your Ranger and Druid should consider is that Masters of the Wild classes abandoning a companion animal in a foreign land/terrain/climate, or the depths of a dungeon where most animals would not be comfortable, as an evil act, and that even neutral or evil Druids/Rangers would generally be against this practice.

Answer 2

I know that a Druid can release an animal companion from service and get another one (or replace a dead one) for 24 hours of interrupted ritual. Is it the same for Ranger?

Yes, everything is the same except that the ranger is treated as a lower-level druid.

How does summoning happen exactly? Do the animals just pop into existence like a Summon Monster spell or does the Druid or the Ranger try to call an animal into their service with their rituals? Can they call any kind of animal regardless of the biome they are in?

This is… ill-defined. The rules state only that a 24-hour ceremony provides a new animal companion, selected from the list. Other supplements (most notably the It’s Hot/Cold/Wet/Crowded/Not Outside series) provide alternate lists for druids in particular environments, and most campaign settings also tweak the lists by region or whatever, which implies that the animal you get is dependent on where you are… or maybe on where you’re from. It’s not really stated one way or another.

Ultimately, it’s up to the DM. I have tended to play it that the druid must find the animal first, and then perform the 24-hour ceremony to bond it, but it could just as easily be a 24-hour ceremony beseeching nature for the companion of choice, which is called to the druid regardless of local availability. (this would not be like summon nature’s ally, as those are very temporary, but a Conjuration (Calling) effect, like a druid’s version of planar ally or planar binding)

It could be that a druid is specifically empowered by the natural environment in which he was trained, or where he grew up, or where he currently finds himself, and so the answer to the call is performed by whichever of those is true and thus the animals available are limited by those environments, or it could be that all of nature at once empowers him and supports him, and any animal is available.

It could be that the ceremony requires deep knowledge of the animal in question, knowledge only gained through first-hand experience, or it could be that the druid merely describes the features he’s looking for and nature provides just the thing.

Any of these are possible interpretation of the rules, and have more to do with the setting of the game than they do with the druid himself. These are cases where Wizards has not only allowed you, as DM, to make a call, but required you to do so.

For balance’s sake, I recommend putting some kind of limitation on it. The druid is fantastically powerful, and while the animal companion is the least of the trifecta (spellcasting, wild shape, animal companion), it’s still really potent. So discuss this with your players and consider the setting you’re playing in, and come to a decision.

When an animal companion dies, do they disappear like how a creature summoned by a Summon Monster would die, or do they die like a normal animal?

They die, like a normal animal or like a creature called with Conjuration (Calling). They definitely aren’t summoned, and therefore do not simply disappear. I cannot prove a negative, but nothing references the Conjuration (Summoning) rules and animal companions are never stated to be affected by anti-summoning spells like magic circle against evil.