How can I tell if damage to my tree trunk is due to birds or termites?

Get thee an Arborist.

Watch for termites to take flight at dusk. You may see more bird activity then, too. It’s a feeding frenzy if the termites are flying.
Also, look for seeds or nuts to be stuffed in the holes. Peel back some bark and see if there are tracks or straight holes.

Termites swarm around this time of year for reproduction. When they are feeding you can’t see them. After finding a swarm in my garage I know all about those little bastards.

If the damage is due to birds, that can only be because they are drilling for insects… so the insects will be the problem to solve either way.

I had a similar symptom (rings of holes around the tree) and was told that it was definitely birds. Termites would not make rings at the same level.

Could it be Sapsuckers? They are the ones who make small holes in the main trunk or large branches of trees. A call to an arborist sounds in order.

If you see sawdust-like material below the holes then bark beetles may be the cause.

insects, sapsuckers and juniper tree damage

Beetles first, then sapsuckers show up for the beetle buffet.

@gailcalled is on the right track.
If the holes are at least an eighth of an inch in diameter and look so perfect that it looks like they were drilled then Bark Beatles would be the culprit.

I doubt that it’s likely to be termites. My understanding of termites in North America is that they generally attack dead and processed wood, not living trees. (Wikipedia seems to bear this out, though I haven’t actually done much research beyond the first paragraph there.)

I think that @gailcalled nailed it. If there are insects at or below the surface of the tree bark, then it may be likely that birds are seeking, attacking or preying on them and causing additional damage, but birds also don’t have any reason to attack healthy, living trees. They don’t eat ‘em, but they eat things that are in ‘em and on ‘em, and make nests in them (including in the hollows of otherwise unhealthy or damaged trees).

I agree with @CWOTUS, in that I have never heard of termites attacking a living plant. They live in the Earth and make mud runs at night so they’re not exposed to daylight/predators.

I think gailcalled it again.

Sapsuckers here also drill holes in my cedar siding on the house to get at insect larvae; they can hear the rustling.