Answer:
Incidentally
Step-by-step explanation:
Transition word or transition phrase is a word or group of word that highlights the relationship between the paragraphs, speech and sentences. These words helps in building the signals and showing the ways the ideas are related to each other. The transition word helps in building the bridge between the ideas. In the given sentences, the transition word used is 'Incidentally'. There is a shift in the idea from the first sentence to the second. In the first sentence the increase in the number of the eagles have been highlighted. Whereas, in the second line, the fall in the number of the eagles have been highlighted. Therefore, a contrasting transition word is required to be added.