Your house is not short of birds. They turn up every day.
Stand outside near dusk. Groups wheel above the roof, a few even land at the edge of the entrance hole. Then they leave.
You have changed the external sound already. Maybe you added internal sound too. Same nest count.
What you are seeing
Birds hovering outside the hole, slow to commit or never committing.
Birds that get through the first entrance (the hole the birds fly in from outside) and then loop around in that first space instead of going deeper. The old name for it is the roaming room, as though it were built for looping.
A wide smear of droppings on the wall outside the second entrance (the second door that birds will pass through in your bird house).
Tweeters on, aroma sprayed, still hardly any nests.
These arrive together, and they all mean one thing: the birds want in, and getting in is a struggle.
The common misreading: it must be the sound
Sound is the first suspect for almost everyone. External not pulling? Swap it. Internal not settling them? Add more.
I sell equipment, so this is a strange thing for me to say. A bird that cannot get in never hears your new tweeter.
The second misreading is treating a crowded entrance as good news. Would you not rather have all of them inside? A bird parked outside has not made up its mind.
The third one is the painful one. An owner looks down his row, sees every house in the same state, and decides the area has no birds left.
The birds are still there. They arrive daily, do one lap, feel wrong, and go elsewhere. You see fewer birds. The bird sees a row of houses with no way in. Two different problems, and the second one is fixable.
How to check
Three things on the entrance decide it: the level line, the angle, and the light. Together they are layer one of the MDK Swiftlet House Diagnosis Method, ahead of airflow, temperature and humidity. No entry, nothing inside counts yet.
Step one, count your holes properly
First entrance: where the bird enters from outside. Second entrance: the first doorway it meets inside. Air well design? Then the air well is your first entrance.
Miscount here and every later step is wrong. Our rule is that the first entrance should be visible from the second. Skip the air well and you are testing two other openings. The rule no longer fits your house, while you believe you passed it.
Step two, the level line
Stand at the second entrance. Is there any angle from which you can see the first one?
Height is only half of it. Sideways offset counts just as much. Two openings out of line, vertically or sideways, force the bird into a sharp turn as it comes in.
Line of sight means that stretch flows. No line of sight means a bend too sharp somewhere, or a drop too abrupt.
A swiftlet comes in fast. Ask it for an awkward manoeuvre at the last second and it declines. It has the whole sky, and your house is not worth the risk.
The commonest fault I see is a plain structure made twisty. Tight bend, another tight bend, a narrow squeeze, and finally the bird is in. The builder had reasons for it. Too bright otherwise. Wanted more nesting space. The birds are not persuaded.
Step three, the angle, which never comes alone
By angle people usually mean how steeply the path drops between the outer hole and the second entrance.
The trap is that steepness is not a stand-alone figure. It comes tied to distance. Picture the bird landing like a plane. Steepen the approach and the runway shortens with it, until the plane cannot come down.
Too narrow, too steep, too long, too wide. Any of the four breaks it, and they pull on each other. Adjust one and the other three move.
Which is why there is nothing to copy. A layout that works in another house can be wrong in yours. Even your own second house, the good one, does not transfer as it is.
Step four, the light, but which light
Three lights meet at an entrance.
Natural light, meaning the brightness of the house itself. The setting sun, meaning whether it beams straight in during that short window before dark. And any lamp you fitted yourself.
For the lamp, one question comes first. Why is it there? To keep predators off, to draw insects, or to draw birds? Each purpose is fitted differently, and a lamp fitted with the wrong purpose in mind is just a lamp that is on.
Too little light and the bird has to grope its way in, and groping scares it. It just gets slower. And slow is the expensive part of this business.
Light has its own article: does a swiftlet house need to be completely dark. One warning: do not read it and fit a light by yourself. A lamp in the wrong spot does more harm than no lamp.
Two checks for today
One. Count the nests inside. Zero nests, and the birds simply do not like coming in. Nothing further to explain.
Two. If there are a fair number of nests, walk over to the wall just outside the second and the third entrance. Heavy droppings there mean the birds hovered a long time before each entry, working up the nerve. Smooth that stretch and they settle much faster.
Check the way out too. Nobody enters a place they are not sure of leaving.
When does equipment come in
Year in, year out we look at houses online, close to 150 of them by now. In roughly nine out of ten, the entrance is where it is stuck, and that is why the birds are slow to move in. Most had been diagnosed from airflow, temperature, humidity and sound onwards, so the fault stayed hidden.
An entrance fault is a road fault, not a tweeter fault. Sound cannot pave a road.
Equipment still matters. Once the birds are getting in, sound, aroma and planks each earn their place. Only the order cannot flip.
So we push nothing before we have seen the house. Once we know which stretch is stuck, we know what to change and whether you need to spend at all. No diagnosis reason, no sale. That is the Diagnosis Method in practice. Diagnosis first, prescription second.
Next step
Leave the sound alone. Buy nothing yet.
Film one video. Go in from the entrance hole the way the birds do, talking as you go, and record the internal sound and then the external sound. A phone is fine.
Send them to our customer service. It is free. If we need more after looking, we will ask. No need to prepare everything at once.
A house where the birds hover and turn away is rarely wrong everywhere. Usually one stretch on the way in has one thing stuck. Find it, and the job is smaller than you fear.