Whether or not the plants are 'choking' each other would be a function of how congested the roots are in the entire soil mass. Root congestion restricts growth because the soil becomes packed with 'conductive' roots, roots the primary function of which is to move water and nutrients, rather than to gather them. This leaves a reduced volume of soil to support the fine hair roots that do all the real work. The 'center' you refer to would be called the 'crown'. If the roots have filled the pot and are restricting growth, you should consider repotting/root pruning or separating and repotting the plants in the future, but winter is a poor time to consider work as major as that. Instead, wait until early summer when the plant(s) have gained some energy and they are better able to tolerate the stress. If the smaller plant is an offset from the larger, you can simply cut them apart with a longitudinal cut so each has a healthy portion of the root system. Dust the cut with powdered sulfur if you want, to help thwart any rot organisms that might want to wreck your day. If the plants are individuals, tease or cut the root mass apart to separate the plants & repot. Don't be afraid to cut the plants back and prune roots. This type of treatment forces growth from cells closer to the root systems, which are ontogenetically younger (juvenile) and more vigorous, which is where the term rejuvenation pruning comes from. Al

I'm new to house plants, but i've killed one birds nest fern before and the second is thriving (this is how we get to be good at caring for a particular kind of plant it seems you have to kill one and learn from your mistakes). What i've found is that it's easiest to water from UNDER the plant. What i mean is when the surface of the soil in the pot is dry (check it every other day folks you don't want it to get starved). Take it and set it in a shallow bowl of water mixed with the right amounts of liquid miracle grow houseplant food. Let it soak maybe 15-30minutes or until either all the water is absorbed or the surface of the soil is moist. If the soil is dry on the top and the water is all absorbed add more and check every so often. when the soil is thoroughly moist, remove the plant and drain for a few minutes (i stick it in the kitchen sink) and then return it to it's normal home. My 4 inch plastic pots sit inside glazed ceramic containers to dress them up and keep moisture from getting on the windowsill. Watering from underneath avoids crown rot (which i understand to be a problem common to this plant), and it assures even moisture in the soil, i've noted it's hard to get the soil fully watered when watering from 'overhead' esp since i have a 4inch pot for my birdsnest fern. Also i noticed in TOO HIGH lighting conditions the leaves get really really pale almost white even after just one day. When not watered enough the leaves get really dry and start getting brown spots at the edges. With crown rot i started loosing leaves rapidly and no new leaves would spring up out of the crown. I can tell my plant is healthy the way i've been caring for it now (after a few months after bringing it home from the nursery) the fronds have gotten darker (they started almost yellow and are now darker)and i'm getting new buds poking through the crown. My birdsnest fern is in a west facing window with a 6 foot porch overhang. It gets gentle light until the end of the day just before the sun sinks over the horizon. It doesn't seem to prefer bright light, nice 'understory' kind of filtered light seems to suit it well. (like what you'd get under a tree) I've started watering all my houseplants from underneath (with exception of my orchid which gets misted). The african violets and my birdsnest ferns love being watered this way from my experience. I've only had these about 6 months but for now it seems everything's going quite well.

I used to run a range of greenhouses and for sure there would be a couple wrens to nest in the hanging baskets. I'd put a sign on it to not water it and they were fine with people coming and going and doing their thing, with one or two ugly baskets going dry so they could fledge. They're tidy parents who as soon as the chicks are able to fledge get them up and out of there faster than any bird I've ever seen. Love my wrens!

They are no different in Europe than anywhere else. It is true in the animal world it is hard to find a species that's completely innocent. Bluebirds will also kill and take over a nest if they have too. Barn swallows can do the same. I can give you a link with a story about swallows sealing a nest that a sparrow took over, and they sealed it with a sparrow inside (but the link is not in English). Swifts in Europe often take over a nest by killing the birds with its claws. The american cowbird is an angel compared to the European cuckoo bird :) I could continue with these kind of stories forever. Any way, I don't have a problem with your or anybody else's advise, but you should list all the possible solutions, not just YOUR favorite.