Were they planted as one year whips or older larger trees? You don't say how long the branch is but 13 pears seems like an awful lot of pears to have on brach of a tree. If you are concerned about the branch breaking then I would most definately thin. Normally pears should be thinned to one or possibly two per cluster with one cluster about every 6 inches. Yes remove any small or damaged pears leaving only the largest best looking specimens. This will give you much larger fruit and avoid damage from breaking.

On older trees, I generally don't bother -- if there is a heavy set of fruit, they are smaller, but generally still a good size -- after all, I don't need these enormous pears that are big enough to serve 2 people to pack into my lunch, and smaller pears pack better into canning jars, too.

But, on young trees, definitely thin so they don't break the tree.

macmanmatty: I don't know their age. They were about 3-4' tall when we purchased them in late 2008. Due to a spring freeze, they didn't bear fruit in summer 2009. I'll thin some from that one branch that has so many. Thanks.

denninmi: Thanks very much for the tips!

LD