The Rio Grande cichlid (Herichthys cyanoguttatus) has been established in the Greater New Orleans Metropolitan Area (GNOMA) for at least 20 years. It is often the most common fish species in urban canals and has also been found in natural waterways outside of the GNOMA. The effects and potential for further spread of H. cyanoguttatus is uncertain. My research addressed how extensive the cichlids spread in the GNOMA, how H. cyanoguttatus interacted with L. macrochirus, a native fish, and what salinity tolerance this species has. Surveys on Lake Pontchartrain and in the GNOMA indicated that H. cyanoguttatus is well established in urban habitats. These surveys also indicate that H. cyanoguttatus has spread rapidly into Bayou Saint John and City Park in recent years and that H. cyanoguttatus populations were relatively unaffected by Hurricanes Katrina and Rita. There is little evidence that H. cyanoguttatus has become established outside of the GNOMA, but this lack of persistence cannot be explained by abiotic variables I measured. Salinity may be a factor and this was measured in growth trials of H. cyanoguttatus. Salinities up to 16 ppt, however, had no significant effect on H. cyanoguttatus growth. Interspecific behavioral experiments were conducted to examine potential biotic interactions with native fish species. Prior resident trials indicated that H. cyanoguttatus was aggressive whether holding territory or not, and that native bluegill (Lepomis macrochirus) was only aggressive while holding territory. Feeding experiments were performed to examine biotic interactions between H. cyanoguttatus and L. macrochirus. Lepomis macrochirus grew faster than H. cyanoguttatus when inter- and intraspecific trials were compared; however, no significant growth differences were seen when trials were structured with L. macrochirus as prior residents. The major findings of my research are a high salinity tolerance of H. cyanoguttatus, a potential mechanism for H. cyanoguttatus affecting native fishes through aggression as residents and invaders, and the presence of H. cyanoguttatus throughout the GNOMA, before and after the hurricanes.

Interspecific aggression of meadow pipit (Anthus pratensis) towards treepipit (A. trivialis), whinchat (Saxicola rubetra) and skylark (Alauda arvensis) and interspecific aggression of whinchat towards meadow pipit was tested in playback experiments at the beginning of breeding cycle (both species) and during the brood feeding period (whinchat only). Neither meadow pipits nor whinchats responded aggressively to the playback of the heterospecific songs. Whinchats, however, chased or attacked meadow pipits that approached it in response to the meadow pipit songs in the brood feeding period. I suggest that the aggressive behaviour in whinchat is triggered rather by visual than acoustic cues. Another series of playback experiments with meadow pipits was carried out to investigate the effect of the sensitisation caused by previous playback of the conspecific song on performance during the playback of the tree pipit song 30 minutes later. No clear effect was discovered, but some of meadow pipits reacted in a way more characteristic for the intraspecific experiments.