I found this bumble bee today underneath a sallow tree that had been buzzing with life yesterday .I am wondering if this is bird predation or some other cause.
No interactions present.
http://www.bumblebee.org, more bumble bees die from parasitism than from predation. Have a look at the site for more information.
Equally, of course, it's been a hard winter, and it may just have succumbed to the elements.
The fact that it hasn't been eaten suggests it wasn't a predator.
your link,I felt that if it was a bird the body would have been more broken up,in this case the wings are even intact.On the other hand if it was a parasite,it devoured the "softer" body parts at both ends, very efficently .It was very attached to the grass stem which to me makes the conopid fly look like the culprit (if it was a parasite).
Lat/Lng: 52.6, -7.9
OS grid ref: SF0616