In a first experiment, dorsomedial forebrain ablated birds showed similar homeward orientation when compared to untreated controls independent of whether the birds were released from a previous training site or a site they had never been before. However, although all control birds returned to the home loft, only 2 of 28 birds with lesions homed successfully. In a subsequent experiment, both sham operated control birds and birds with lesions of the visual Wulst homed successfully when released only 800 m from and in full view of their respective home lofts. Pigeons with dorsomedial forebrain lesions, however, failed to return to their respective home lofts. The results show that (1) the avian dorsomedial forebrain plays a critical role in that step of the homing process by which a pigeon returns to its home loft once in its vicinity, and that (2) the failure to reassociate with the home loft is a likely result of deficient recognition of the home loft and/or its surrounding area. In an additional experiment, pigeons with Wulst lesions were shown to orient as controls and to successfully return to the home loft when released from two distant sites. This experiment demonstrated that the avian Wulst plays no necessary role in the homing behavior of pigeons.
In a series of experiments which involved only short distance experimental releases (800 m or less and within view of the home loft), it was demonstrated that dorsomedial forebrain ablated pigeons generally failed to reassociate with their home loft if the postablation experimental release took place soon postablation or if during the time between ablation and experimental release they were kept away from their home loft. In contrast, if dorsomedial forebrain ablated pigeons were allowed to recover at their home loft prior to experimental release, they succeeded in associating with their home loft in a manner similar to controls. However, only postablation exposure to a pigeon's own loft was sufficient to permit continued home loft association. Pigeons from one loft failed to associate with a foreign postablation recovery loft when released within sight of it. The results show that (1) dorsomedial forebrain ablations result in pigeons which no longer succeed in associating with their home loft; (2) recovery from failed home loft association behavior is possible with postablation exposure to the home loft, and (3) a pigeon's previous association with a loft was a precondition if postablation association was to be affected. The results suggest that dorsomedial forebrain ablated pigeons retain something like a 'home loft trace' which they can use to mediate retrieval and reformation of the recognition properties needed for proper home loft association.
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