Many potential reasons for the decline of the Loggerhead Shrike have been suggested, including:
loss of habitat on the breeding grounds and wintering grounds
collisions with vehicles
adverse weather conditions
competition with other species
competition between migrating and non-migrating Loggerhead Shrikes on the wintering grounds
Several factors have destroyed shrike habitat, including:
reforestation efforts and natural succession
industrial and housing development
changing agricultural practices
However, loss of breeding habitat does not fully explain the reduction in shrike numbers in many areas, since habitat that is apparently suitable goes unused each year.
Further research is required to better understand the cause(s) of the decline. It is likely that a combination of factors is affecting shrike populations, possibly at different times throughout the bird’s life cycle. For example, adverse climatic trends on the breeding grounds may reduce nesting success, while collisions with vehicles may decrease the survival rate during migration. According to most research, chemical contaminants are not a major cause of decline. However, studies have not been done on the impact of newer pesticides, such as indirect effects from neonicotinoids that may decrease the supply of prey.