Mental Tethering

Through their binding magics, Druids are able to tether the minds of animals to their own, creating a telepathic channel in which the pair can communicate. Audibly their sounds remain fully animalistic as their physical bodies are not altered to allow human speech. Initially these exchanges are simple, based on pictures and emotions or perhaps with a few words the animal may have heard before. This can be advantageous if the Druid wants to encourage a snake to go another direction, get a wild horse to allow a ride somewhere, or ask a cat what it might have seen earlier. There is no guarantee that the animal will comply, but it does offer the Druid a way to be heard and for the animal to respond.
Animal Companions
A Druid can bind to any animal, however they commonly choose animal types that would be viewed as pets since a Druid walking a dog is less likely to draw attention than one walking a bear. Although they may be viewed outwardly as pets, may require the Druid to provide necessities, and to care for them, Druidic Companions are usually viewed as close friends or family to the Druid. Without intervention through magics, potions, or similar means, a Druidic companion has the same lifespan or slightly better than a normal member of its species.

The longer the Druid and animal are bound, the deeper their bond, eventually creating a loyal companion. It is unknown whether the Druid's magic actually bolsters the animal's intelligence or if it is a byproduct of exposure and longevity, but animal companions appear to have their intelligence enhanced. With time, patience, and training, the companion is capable of possessing a robust vocabulary, speaking grammatically correct, understanding complex concepts, and expressing their own ideas. As with a human, exposure is beneficial to grow their language skills, such as through music, television, and hearing others converse.
In addition to greater intelligence, or because of it, the companion's personality becomes more evident as well. In the case of Oberon, Siodhachan's Irish wolfhound companion, he possessed a human level of intelligence with drives and interests that were still very canine (poodle-mating, meat-loving, squirrel-hating). Note that it is important that the Druid understand these animal instincts and provide the occassional outlet to express them, such as letting a hound run or a bird fly free.
The companion can only communicate telepathically with the individual(s) they are bound to. It is possible for multiple Druids to bind to the same animal or a Druid to bind to multiple animals. A Druid can also bind to multiple animals and further bind those animals together so they can all share the same telepathic circuit. Dieties and supernatural beings who have control over animals, the animal type, and/or telepathy can use these powers to communicate with and potentially control the companion despite the Druid link.
Unbinding an Animal/Companion
There are many reasons a Druid may decide to unbind an animal or companion. The unbinding severs the telepathic connection and generally does no harm to the animal who has been bound on a short-term basis. When long-term companions are unbound, several problems can arise such as the companion being emotionally devastated, growing angry or confused and lashing out at the Druid, or the animal's refusal to leave the Druid alone afterwards. Unbinding long-term connections must be done with care and is typically a last resort. Even when the companion is dying, the Druid will endure the tether in order to provide comfort to the animal.
Elementals

Elementals, known as Furies by the Alerans, are spirits of biomes, earthly elements, tectonic plates, and similar terrestrial constructs. Druids have the ability to call upon these beings and communicate telepathically with them. Elementals do not communicate in any language, but instead seem to communicate by emotion-images, which after a little bit of practice can be interpreted as words by Druids.
Druids and Elementals are allies by default, neutral if not. Heinous grievances against the earth or the Elemental will make the Druid an enemy, however Gaia may intervene first should the Druid violate their oaths to her. Elementals are a vital part of the Druid's arsenal since they are not bound by the same 'harm none' restrictions and are able to react more quickly in defense of the earth than the earth can itself through natural processes. Note that powerful Druids can communicate with Elementals all over the world, however the Elementals themselves are locked to their specific biomes. A desert elemental in the Sahara has no conceivable path to reach the American west desert.
If summoned by a Druid to a situation where immediate threats to the earth are evident, the Elemental is likely to accede to the Druid's requests, much like the Ents in Lord of the Rings did upon seeing the destruction of forests near Isengard. However, for lesser favors such as altering the terrain or concealing an item in the ground, the Druid may need to barter, especially if the Elemental and Druid are not already acquainted. Unlike the Alerans who have notable mastery over their elemental Furies, Druids have no such power and must use persuasion.