You may have noticed the FOSS Tree Swallow crew tossing out nesting material from some boxes in the last week or so. As well as having kept the entrance holes covered until the swallows arrived this spring, we have also been evicting House Sparrows from boxes in order to deter them from taking over. Our efforts have produced some success ... there are more swallows than ever this year in the field.
House Sparrows are extremely determined and aggressive. They will kill adult swallows and nestlings in the boxes and even build their own nest on top of the dead birds!
Although the images posted here of dead swallows we have recently found are difficult to look at, they do illustrate how ruthless sparrows can be and why we need to continue with the "evictions".
House Sparrows are an "exotic", non-native, invasive species and as such are not protected under the Migratory Bird Treaty Act. Nestbox monitors are allowed to remove their nests, particularly when they compete with protected birds like the Tree Swallow.