2 possible things you might do: One - put a feather in the box w/the trap & one at the hole to attract the HOSP.
OR - reverse boxes(or nests- probably too late w/babies inside). Good luck.

Thanks for the suggestions, easternmass. I did not guess about the first option, but the second option concerned me if the bluebirds would still go to the old spot with the new house and get caught and I am not there to release them. But I will try it when I am back, and I will just replace the nest. Anyway there is nothing to risk with anymore, at least the babies will have a chance, and I might have some time as well because the HOSP seems to attack during morning and evening hours, when the mylar tape does not reflect the sun when the birdhouse is somewhat shaded.

I would like to update my case. The HOSP made one more attempt (when the wounded BB baby was still alive, but seemed could not compete for food), but that time I noticed that BB parents behaved strange and hesitated to enter the house, though they did not sound very concerned. Just in case I approached the house and stuck my finger in, as soon as I puled it out, the HOSP male flew out and I even touched him, BB parents chased him away. If I knew it before I could catch him. I checked the BB babies and they were fine but scared. I was sure that day the HOSP would not return, The next morning, 2 days later after the first HOSP attack, I found the wounded BB dead and the BB female tried to carry him out. I made her leave the house, took out and disposed the dead BB (smell was already bad).
I decided to exploit the smartness of the HOSP against him. As I mentioned he leaned that the spooker was not dangerous, and fishing line was also useless against him. I opened the front wall and left it open to serve as a perch site. Instead I attached two-entry patch and stuck it with a scotch tape. I was certain that the HOSP would be too smart to ignore the sudden transformation of the BB house. Besides the house started looking more scary, like having two big eyes. The other thing I pursued with this transformation is to have emergency exit or entrance, since the HOSP would not be able to block the both holes at the same time. With the 2 holes there was more light inside and I could check the nestlings without opening the door. At first the BB parents were confused, but shortly they figured out their babies were still inside and doing well.

As the result I have not seen the HOSP around anymore, the BB parents became more defensive and the three BB babies have fledged yesterday. Now I need an advice or opinion:
a) I take the BB house down until I significantly reduce HOSP population. Actually the HOSP infestation was not too bad first, but then numerous young HOSPs fledged from the neighbors house and the area became heavily infested. That house is like the HOSP farm, and at the same time HOSPs would almost never seat on my roof.
b) I keep the BB house with the transformed front wall,
c) I restore the house to its original shape, where I can set up a trap as needed.

Thanks.

This post was edited by stal14 on Wed, Jul 2, 14 at 11:24

I had a similar problem with HOSPs this spring. They chased my bluebirds away and staked out both houses. I ordered the elevator trap and managed to get rid of all HOSPs. That is the only thing you can do because they are relentless and will not give up. The trap only works if you can get a bird in it. Once you have one HOSP in the trap, you will catch all the rest.

The traps work well. DSRT(deluxe repeating sparrow trap) works well-bait it with white bread. Vanert's Nesting box trap works also. You do have to keep a closer eye on that one because any bird can be trapped in there.

It is best to be as ruthless towards the hosp as they are towards the bb's. They get no mercy from me when I finally get them in one of traps. They should be euthanized (hosp) as letting them loose into another area only shifts the problem. It is legal to dispose of them for they are a non native bird.

Am glad to hear that the rest of your babies were able to fledge. I had a hosp attack on the nestlings-three of five were injured, one that had gotten pecked worst of all. My son was in the right place at the right time when he noticed hosp and bb's battling. We immediately did what we could by giving aid-cleaned the wounds and applied BNW a natural ointment for humans.to the babies that got pecked, refreshed with a new nest and kept eyes on them for severalldays-Happy to say all five fledged including the wounded ones. Yes!

After the initial HOSP attack I built a repeating trap, and by now it trapped about 15 HOSPs, and interesting that all of them were females. Today the trap got a cardinal male. Probably he was there for 6-8 hours and I hoped that there was enough food left. I never thought the bird could fit inside of the trap elevator, but it did, and it seems he terrified three HOSPs, which were in the trap for a while. It was getting late so I did not have time to make any pictures, besides I spent some time trying to pull him out safely through the rubber hatch which originally was not designed for such big size, and the bird was not cooperating either when biting my fingers and cardinals bite hard. At last I captured him in a way that he would not bite me anymore and pulled him out. Before releasing I just held the cardinal for a minute or two because when I would have another chance to see such a beautiful bird so close.
Juanital, it is too bad I did not know that I could save the lost BB baby if I knew about the steps you applied to your nestlings. Thanks for the information, next time I will know what to do with wounded birds, hopefully I would not need to use the protocol.