Grundsätzlich muss man sich erst einmal immer an den Wortlaut halten:
Animal Companion (Ex)
A druid may begin play with an animal companion selected from the following list: badger, camel, dire rat, dog, riding dog, eagle, hawk, horse (light or heavy), owl, pony, snake (Small or Medium viper), or wolf. If the campaign takes place wholly or partly in an aquatic environment, the following creatures are also available: porpoise, Medium shark, and squid. This animal is a loyal companion that accompanies the druid on her adventures as appropriate for its kind.
A 1st-level druid’s companion is completely typical for its kind except as noted below. As a druid advances in level, the animal’s power increases as shown on the table. If a druid releases her companion from service, she may gain a new one by performing a ceremony requiring 24 uninterrupted hours of prayer. This ceremony can also replace an animal companion that has perished.
A druid of 4th level or higher may select from alternative lists of animals. Should she select an animal companion from one of these alternative lists, the creature gains abilities as if the character’s druid level were lower than it actually is. Subtract the value indicated in the appropriate list header from the character’s druid level and compare the result with the druid level entry on the table to determine the animal companion’s powers. (If this adjustment would reduce the druid’s effective level to 0 or lower, she can’t have that animal as a companion.)
Quelle:
http://www.d20srd.org/srd/classes/druid.htm#animalCompanionDann wird man sich auch dessen bewusst, dass D&D 3.0 und D&D 3.5 sich teilweise ziemlich unterscheiden können in einigen Aspekten. Das verwenden von altem D&D 3.0 Material kann verwirren.
Von der Regel eines (einzigen) Tiergefährten kann es Ausnahmen geben, wenn eine entsprechende PrC z.B. ergriffen wird, die speziellere Regeln besitzt (siehe unten im Link).
Dann googlet man und findet dieses sehr hilfreiche Topic, wo eigentlich alles drin steht, was das Herz (bzgl. dieser Thematik) begehrt:
http://paizo.com/threads/rzs2g3a7?Multiple-Animal-Companions-in-35