The Non-Indigenous Ant, Solenopsis invicta, Reduces Loggerhead Shrike and Native Insect Abundance

The red imported fire ant (Solenopsis invicta Buren) is an aggressive, non-indigenous species that is a threat to native biota in the southeastern United States. We determined the effect of S. invicta on loggerhead shrike (Lanius ludovicianus L.) abundance and investigated a possible mechanism of impact, which is a reduction in insect prey availability. We used a fire ant bait (hydramethylnon) to reduce fire ant populations on one randomly chosen member of each of five pairs of 202-ha study areas in the Texas coastal Bend region, and also measured shrike relative abundance and a volumetric index of insect biomass on the study areas. Loggerhead shrike relative abundance was assessed at five counting stations established along 3.2-km transects through prairie habitat on each study area during the fall of 1992 and 1993. We sampled non-S. invicta invertebrates with 13.3-L capacity UV light traps and found that insect volume, species richness, and diversity were greater on treated sites. More shrikes were observed on areas where S. invicta populations had been reduced. Both insect biomass and shrike abundance were negatively correlated to the level of S. invicta infestation. Our data suggest that shrikes may avoid areas on wintering habitats that have been invaded by S. invicta and that this avoidance may result from reduced insect availability

Shearwaters sometimes take long homing detours when denied natural outward journey information

The cognitive processes (learning and processing of information) underpinning the long-distance navigation of birds are poorly understood. Here, we used the homing motivation of the Manx shearwater to investigate navigational decision making in a wild bird by displacing them 294 km to the far side of a large island (the island of Ireland). Since shearwaters are reluctant to fly over land, the island blocked the direct route home, forcing a navigational decision. Further still, on the far side of the obstacle, we chose a release site where the use of local knowledge could facilitate a 20% improvement in route efficiency if shearwaters were able to anticipate and avoid a large inlet giving the appearance of open water in the home direction. We found that no shearwater took the most efficient initial route home, but instead oriented in the home direction (even once the obstacle became visible). Upon reaching the obstacle, four shearwaters subsequently circumnavigated the land mass via the long route, travelling a further 900 km as a result. Hence, despite readily orienting homewards immediately after displacement, shearwaters seem unaware of the scale of the obstacle formed by a large land mass despite this being a prominent feature of their regular foraging environment