Here is a snippet of last night’s evening loon concert. The female is on the nest  and she is listening to tremolos and yodels coming from a distance. The yodels are most likely from her mate (only males yodel). The tremolos are from neighboring loons. Since loons haven’t mastered texting yet, these calls are what they use to keep tabs on the rest of the community. Sounds like the male is saying “We’re still here and we intend to stay. Don’t mess with us!”