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Migrating birds "hug" land masses, and radar can capture spectacular massings of birds in season. A very famous migration chokepoint which also produces spectacular radar images is across the Straits of Gibraltar, as birds fly back and forth in season between Europe and Africa.
A radar transceiver of the National Oceanographic and Atmospheric Administration (NOAA) is located in Key West, Florida, in the path of a migratory bird flyway.
The spring migration of land birds and shorebirds across the Gulf of Mexico begins in the first and second week of March, reaches a peak in late April/early May, and is essentially over by the third week in May.
The doppler radar image loop shows a late night/early morning bird migration episode on 28 April 2002. Ornithologists estimate that nearly 10,000 birds per mile are flying through the dark green radar reflectivity areas (25-30 DBZ).
Okay, the scale at left is echo intensity (reflectivity), measured in dBZ (decibels of Z, where Z represents the energy reflected back to the radar).
Recently, Bob has been migrating back and forth across a national border. Borders are of huge concern to human beings.
Notice that Havana and Cuba are at screen bottom; the distance from Key West to Havana is 106 miles / 170 km. Notice that the birds don't give a flying fuck about the borders or sovereignties of the two hostile nations; they go where they like when they like.
The activities -- economic, military -- of nations can imperil animal populations. Whooping cranes (naturally) winter along the Gulf of Mexico in Texas and summer in the northern Prairie Provinces of Canada; the long-lasting, nearly permanent political friendship between the two nations has been a big factor in human-assisted efforts to pull the species back from extinction.
But birds which divide their time between the USA and Cuba are likely to suffer from the near absence of scientific cooperation between the hostile nations. Political tensions are also increasing between the USA and Venezuela.
Many land animals along the USA-Mexico border have suffered badly as the USA has militarized its side in response to narcotics smuggling and illegal immigration. Large zones are now in constant bright illumination all night, a vast disruption of the animals' nocturnal activities. Likewise the increasing political pressure to erect physical barriers across long stretches of the border will negatively effect animals, by isolating breeding populations and thus lessening genetic diversity, which predictably expresses itself in less resistance to new parasites and diseases.