a large black triangular shaped craft that hovered with small birds circling all around it (maybe a Thunderbird sighting)

well it was a long time ago so you may not be interested but there is one thing about this sighting that i have never heard anyone tell before it was  my sister and i and i was fairly young but we were playing in the backyard when we both saw  black triangle moving low across the horizon from left to right (i can still see it in my mind today very clearly)it was making no noidse at all ,As we watched it move it all of the sudden just stopped and started to what i can best describe as osolating kind of like a spinning coin just about to come to rest, but here is the thing that still strikes me today and never heard of it before and that is a whole bunch of birds were flying circles around it as it osolated in mid air and to this day its a memory that i cannot forget, The birds circling around it were what made it very odd, maybe it was a Thunderbird(a large bird from indian myth) its  the only relative explanation i can come up with.(i have heard that birds are attracted to magnetic fields)
Date is approximate.  PD