It's not semen, it's just extremely watery droppings...
There are 3 parts to a birds droppings, the fecal portion (the solid green/brown part), the Urate (the white portion that is the waste from their kidneys, like our urine), and then there is excess water that passes with the droppings.
Sometimes they will have droppings like this that are nothing but excess-water with some Urate in them (that's why it looks like semen, because it's excess water with a little bit of the white-colored Urates in it)...Usually this happens shortly after they eat something that contains a lot of water, the biggest culprit being most types of fresh Fruit and certain fresh Veggies or Greens...If you ever feed them any of the watery Lettuces, such as Iceberg Lettuce, this will happen (Don't feed them Iceberg or any other type of watery Lettuce, they contain ZERO nutrition, they are nothing but water, stick to the dark, leafy Greens)...If they eat Celery (another veggie not to feed them because it's nothing but water and provides no nutrition) it also does it...
Did your birds eat any type of fresh Fruit or any watery Lettuce or Veggies before they had this dropping?
Usually this isn't a problem or an indication that they are at all sick, it's just because they ingested a lot of excess water that had to be excreted, just like if we drink a beer or we eat a bunch of watermelon, etc., we're going to Urinate a lot. Well birds don't really "urinate", not the way we do, so the excess water just passes with their droppings...When it becomes a problem is if they do it constantly regardless of what they are eating, or if their actual Feces or the solid green/brown portion of their droppings becomes very runny or loose, that's can be an indication that they have some type of GI infection or illness like Giardia, or a parasite...But just passing excess water in their droppings like this is completely normal and does happen based on what they are eating, and is not a problem at all or anything to worry about as long as you see their droppings get increasingly more and more solid as the day goes on. And if you feed them fresh fruit or watery veggies or greens, expect this to happen...That's one of the reasons to avoid the watery lettuces, celery, and a lot of Fruit, because these don't provide any nutrition to them at all, no protein, no vitamins, no minerals, no amino acids, just a lot of water. So stick to the dark, leafy Greens and stay away from watery Veggies like Celery, and only give them fresh Fruit as an occasional treat that they get only 2-3 times a week, and in very small portions, because ALL Fruit is absolutely full of sugar as well, which is turned to fat and stored in their Livers. So fresh Fruit is not at all interchangable with fresh Veggies or dark, leafy Greens, which they need to have every single day because they provide them with needed nutrition...