BuddyPress.org

Nevermind, I googled for that function and found the SVN repo where that function is defined: http://bp-dev.org/phpxref/nav.html?_functions/index.html

The params it takes are:

$defaults = array(
‘item_id’ => false,
‘object’ => ‘user’, // user OR group OR blog OR custom type (if you use filters)
‘type’ => ‘thumb’,
‘avatar_dir’ => ‘avatars’,
‘width’ => false,
‘height’ => false,
‘class’ => ‘avatar’,
‘id’ => false,
‘alt’ => __( ‘Avatar Image’, ‘buddypress’ ),
);

… and the params can be fed into bp_core_fetch_avatar() in the form of “name=value&name=value” pairs as a string.

Hope this helps someone else who is having the same issue.