The east coast of Canada (Nova Scotia, Newfoundland, etcetera) capture and rehabilitate many injured bald eagles every year. A lot of these birds when they get into city areas usually suffer from window or building strike injuries. It is actually a lot more common than most people realize, however the fact that it should happen in your nation's capital on Independence Day does not seem like the most auspicious of omens (if one wished to interpret this event in this manner).
The real omen would be the follow-up on the bird - did it get rescued, was it rehabilitated and if so, was it successfully released? I would think that if one wanted to see this as an omen, seeing this animal healed back to full health and released back to the wild would be a wonder 'sign'. Unfortunately, a lot of these rehab cases can take a long time - some up to a year.
If you are looking for omens I give you two; September 16, 1985 and October 26, 2001. In the fall of 1985 the US Commerce Dept. officially declared that the United States had become a debtor nation. We crossed the point of no return, financially speaking. In the fall of 2001, congress enacted the Patriot Act which began the process of eroding rights guaranteed to citizens in the constitution. We crossed the point of no return, according to our own law.
Regarding the end of the American Empire, I believe the signs are quite prominent and obvious. One does not have to reinterpret the actions of wild animals or consult tea leaves to know the United States is in deep trouble. We've been betrayed by our leaders (of both parties) and now suffer constant pointless war (invented and supported by those same leaders). The American Republic ended in October 2001(*). The American Empire is now a hegemony in decline. The BRIC states are now globally recognized as the rising powers.
America is now a fascist police state. Our nation has crossed the Rubicon. There is no way back.
that's me, hollering from the choir loft...
(*) AMERICAN CONSTITUTIONAL REPUBLIC - by act of congress [May 29, 1790 - October 26, 2001] The state of Rhode Island was the last to ratify the constitution thus making it the Highest Law of the land. Congress deratified constitutional guarantees of liberty (Bill of Rights) when the Patriot Act was passed in the fall of 2001. Subsequent to this act, various additional laws and judicial precedent further eroded restraint of government upon citizens. It is important to note that the majority of constitutional changes were at the Federal level. These changes progressively removed restraints upon government at the expense of personal liberty and privacy.