Poor germination?

I can only suppose it's been a bit colder than usual this spring, as I had hoped to be able to transplant some seedlings by now; the earliest ones are still only just sprouting up in their trays.  Even the early indoor seeds haven't progressed as much as I'd like, though the batch of popcorn seeds have outperformed everything else, coming up in less than a week (I'm still waiting for several different trays to even sprout).

At the allotment, the 300 snap pea seeds have come up very sparsely indeed.  Maybe about 20 have appeared, and it's been long enough I suspect that's it.  The 200 broad bean seeds have a similar showing.  After I sowed both, I covered them with insect mesh, and buried the edges all the way around, to prevent both birds and mice from digging them up, so I'm not sure why the poor germination rate.

On a different note, recall I've been using sheets of wool insulation in my seed trays;  a blue tit has been spotted wrestling little bits from the edges of trays, no doubt to make the coziest nest ever.  Our garden is a great place for wild birds and we often see many, but the blue tit only rarely;  does it nest in our garden, or is it just the occasional visitor?  No idea, but I get a thrill if I see this elusive little bird.