A wood duck hen lays about a dozen eggs over the span of about two weeks. But often other wood duck hens and even hooded mergansers will all lay eggs in the same nest until finally one hen gets to incubate and care for all of them! The most we've seen is 31 eggs one year, about 3 layers deep in the nest box. 25 of these hatched. With smaller clutches of eggs they often all will hatch.
Incubation time for wood ducks and hooded mergansers is identical. However the time from the start of incubation to hatching varies: it's about 30 days, plus or minus a couple of days. Reasons for variation might be cold weather and/or a hen that takes long feeding breaks: if the eggs cool significantly while the hen is out feeding herself each day then they could take longer to develop.
A hen lays approximately a dozen eggs at about one egg per day so the first is about 2 weeks ahead of the last. During those weeks the eggs in the nest are alive but remain cool and thus dormant. Sometimes a hen will rest in the nest box during this time, even overnight, but she has not yet plucked down from her breast nor is she uncovering the eggs and pressing against them, thus the eggs stay cool.
Several hens typically lay eggs in the same nest box (as described below) so when incubation starts there can be many more eggs than were provided by just the hen that does all of the incubating. The start of development is triggered when the hen starts keeping the eggs consistently warm. One of the hen's tasks while incubating is to frequently turn and rearrange the eggs by digging and pulling with her bill to keep them all at the same temperature and developing on the same schedule so they hatch at the same time, within a few hours.
While incubating the hen will spend about 20 to 22 hours every day sitting on the nest ... for a month! Sometimes she leaves both morning and evening to find something to eat and in warm weather (I think) she can stay away longer. Often we've seen a hen leave just once a day (the motion-sensitive cameras make it possible to monitor this), but we also have seen one that left twice a day for several hours each time, and her ducklings hatched too, more or less on time. When the hen returns the camera will often show a lopsided, very large, and strange looking bulge in her neck/chest/throat area. That's her crop: she fills it with food and processes it later, back in the nest.
A wood duck does not bring nesting material into the nest. In the wild the nest typically has crumbles of wood left by woodpeckers or tree decay. In our nest boxes we provide a layer of wood shavings using hamster/gerbil bedding from the pet store. It is completely natural wood, nothing added, and never sawdust because that is too fine and dusty and can suffocate the ducklings.
Both in the wild and in the nest box, the hen adds lots of down by plucking it from her breast. This has two purposes. One is that it removes insulation from her skin to provide better contact with the eggs. The other purpose is this down creates a nice "blanket" that the hen tucks in around her to keep the heat in while on the nest, and that she pulls over the eggs to cover them before leaving to preserve the heat. When the hen is away there is often nothing showing on the cameras at all except for a featureless layer of down and if I open the nest box to count eggs (a duck has little sense of smell and cannot detect that I've done that) the eggs are very toasty warm. Once in a while you'll see the eggs entirely uncovered because something startled her and she left in a hurry.
Ducklings are "precocial", which means that they quickly can run, climb, and swim, within hours of being hatched. In contrast, baby robins and eagles and hummingbirds are not precocial: they need days of feeding before they even open their eyes and weeks of feeding before they are ready to leave the nest. But chickens and ducks and geese are very quickly ready to go. On the day that the ducklings are hatching the mother turns the eggs frequently by digging down with her bill and lifting to turn them. The ducklings can peck their way out of their eggs and they do that entirely on their own, but they aren't strong enough to get out from under other eggs. They come out of the eggs as wet little blobs that can barely move but within hours they have gotten bigger and stronger (still absorbing egg yolk) and lots fluffier. They are very lively at times, bouncing around to practice their jumping and climbing, but with frequent periods of rest in between. They have to get strong quickly because they spend just one night in the nest.
A mother duck does not feed her ducklings. She only can lead them to where the food is and protect them as they feed themselves during the day and rest under her wings at night. The ducklings do nibble on the eggshells and eat the shell membranes as their first rather odd meal. The hen will do that too, and often when they are gone there are not many shells left in the nest. But otherwise the ducklings have to leave the nest to eat.
In the morning (almost always) of the day after they hatch, the hen will start to periodically stand in the nest entrance looking out. She studies the surrounding area, sometimes for 10 minutes, or even more. She's looking for anything that might threaten the ducklings when they leave the nest. Usually she isn't satisfied with the first look around. Sometimes she is, but often she does this multiple times (while those of us watching cheer her on, and wait!).
Finally, she will drop down below the nest box and softly call to the ducklings using a special sound that instinctively activates them and tells them "come here right now!". They respond with lots of loud peeping and start jumping like popcorn, hopping and scrambling up the sides of the nest box, trying to climb out. When they reach the entrance hole they will jump, sometimes after perching there for a while, and flutter and tumble to the ground.
The ducklings can't fly at all, but they do flap their tiny stubby wings anyway and they splay out their little webbed feet, which helps to slow them, and down they go. They're all fluffy and hit the ground (or water if the nest is above a lake or creek) about as hard as a dropped cotton ball would hit. They'll bounce (or bob up), get their feet under them, and then hurry to surround the mother. She keeps calling until the last chick has jumped, then she immediately leads them away. How does she know? If you watch the camera it really looks like maybe she can count, but it's the loud peeping that keeps her waiting: as long as she can hear more ducklings in the nest box she keeps calling.
The length of time from when she decides it's time to leave and starts calling until they have all left the nest forever is only a few minutes. A mother wood duck will care for her ducklings for about 2 months, until they're old enough to go off on their own.
What is Dumping?
Wood ducks, hooded mergansers, and a few other bird species will lay eggs in nests other than their own. Biologists call this "dumping", really, that's the word for it. As mentioned above, our record here is 31 eggs of which 25 hatched. If one hen lays about a dozen, then at least three hens - probably more - provided eggs for those 31.
Hooded mergansers and wood ducks have very similar behaviors and identical incubation times, so they will dump eggs in each other's nests. For example, in 2018 an unusually small brood of 12 consisted of 9 wood duck and 3 hooded merganser ducklings: there are photos in the 2018 log (scroll down to May 21). A hen that dumps an egg has no part in raising its duckling. One hen will do all of the incubating, once that starts, and will care for all of the ducklings after they hatch: both her own and any that hatched with them.
How does it happen?
Before incubation starts a hen will typically spend only 10 minutes up to maybe an hour in the nest when laying so there are many opportunities for different hens to do that during the day. But other hens continue to dump eggs even when incubation has started and the resident hen is in the nest almost all of the time. This might occur when the resident hen is out getting food, which she typically does twice per day for about a half hour to an hour, or sometimes two hours.
However often the cameras show a hen going into an occupied nest box and struggling with the resident hen who tries to discourage it. The videos page on this site has several videos of that: here is one from both inside and outside of the nest that is brief, and here is one where the battle continues for 7 minutes! ... and at the end of that you can see the result: a new egg from the invading hen that the resident hen dutifully pulls into the clutch to take care of.
The resident hen always does most of the fighting while the invading hen mostly puts up with it and just tries to stay for a while. I've never seen blood, injury, or even very many feathers pulled out. Just lots of squawking with biting and shaking, especially targeting the nape of the invader's neck. Often the invader's strategy seems to be to sit on top of the resident hen to sort of pin her down and thus keep her own head up and away from the part of the resident that does all of the biting. And, once in a while, there is no battle: this video shows a resident and an invading hen peacefully sharing the nest box while the latter leaves an egg (one theory: Could they be sisters and thus the biological urge to perpetuate only ones own genes is muted by their relatedness?).
Why do they do that?
Competition for nest sites is part of it: if a hen has an egg ready but no nest site of her own she'll put it where another mother might raise it. But even while laying eggs mostly in a nest that she intends to claim, a hen still might put some eggs in other nests as a survival strategy. Biologists agree that perpetuating ones own genes is an innate driving force for all creatures. Ducks are in the middle of the food chain so their chance of getting eaten or ending in some other way is fairly good. If some of their eggs are in other nests, then some of their descendants might survive even if they don't.
Wood ducks typically have large broods because the survival rate is so low. Little ducklings are even more a part of the menu of other creatures than their parents. Foxes, raccoons, skunks, cats, dogs, coyotes, northern pike, walleyes, muskelunge, bass, herons, hawks, gulls ... the list goes on. One year when a family stayed around our back yard for a while, the count steadily diminished by one or two each day.
Late and Unhatched Eggs
One cause for an egg to develop late might be if the hen "loses" it in the corner of the nest box for a while and it gets cold. This is rare, I think, since she frequently moves them around and the nest box isn't that big. But when the eggs are 3 layers deep, I suppose it could happen. Or an egg might be infertile and not develop at all which is also rare but does occur.
The most significant reason for late hatching is when a hen lays an egg in a nest where incubation has already started (see "dumping" just above). If all of the eggs in the nest have started their development, and then an egg is dumped a bit later, the resident hen will keep it warm and it will develop too. But it started late and so will hatch late. If the timing is just right (well, actually just wrong) it will hatch many hours after the others but before any ducklings have left the nest. Then when jump day morning comes and the others are ready and able to leave the late duckling will not have had the hours of time that it takes for a duckling to get fluffy and stronger. It won't be able to leave with the others.
Sometimes you'll see this on the camera on jump day: one duckling who often looks wet (because he is) is pathetically trying to move but just can't. Or sometimes when I clean out the nest box just after they've left, there is an egg starting to hatch or one that has a live duckling inside, peeping (they do that for a while before they hatch - it's what tells the hen to start turning the eggs even more than she usually does).
What happens to late ducklings and unhatched eggs?
They do not survive. So many people ask about this that I have created a special information page about it. Please follow this link.
Sometimes people ask about the size and position of the nest boxes: it doesn't look like there's enough room, or climbing out looks too hard for the ducklings and jumping down looks too far.
Nest box size
In the wild, wood ducks nest in hollow trees and holes made by (and enlarged by) woodpeckers. These are not typically spacious: the hen will nest in a space just big enough for her body but will refuse to use a space much larger. She needs to be able to cover it and manage it during incubation. People who have tried different sizes of duck houses to see what they prefer all have the same recommendation: each side should be 10 to 12 inches. My nest boxes are about 11 inches.
Nest box height to the door and door size
The hen requires an opening that is well above the nest. It must be at least high enough so that predators such as raccoons cannot reach in and get the eggs. Raccoons will take duck eggs and ducklings too, and a large raccoon will even pull the mother duck out of the nest if it can reach her. For that same reason she wants the entrance to be just barely big enough for her body so that a large predator cannot just climb in.
In the wild, ducklings may have to use their very sharp toenails to hop and climb 6 feet or more upwards to get from a nest deep within a hollow tree up to the opening. In my nest boxes they only have to climb about 10 inches. You can see plastic or wire mesh when watching the cameras which is there to help the little ducks climb the smooth boards of the box.
Nest box height above the ground, or water
When a baby wood duck jumps it might be from only about 5 feet up as for our nest boxes. But in the wild they might be jumping from a hollow tree trunk nest that is 80 feet above the ground: an 8 story drop! Wood duck ducklings can't fly at all, but they do flap their tiny wings and they splay out their little webbed feet, which helps to slow them. They're little balls of fluff and hit the ground about as hard as a dropped cotton ball would hit.
(A bit off topic: but check this amazing video of a Barnacle Goose gosling that jumps from 400 feet up, that's a 40 story drop, lands on jagged rocks, and tumbles down the cliff. Spoiler, but perhaps necessary since otherwise it's hard to watch: the gosling survives! This is normal for them.)
Nest box location
Wild wood ducks will nest up to a mile away from water. But they prefer to be close since a long overland trek can be hazardous for the ducklings. They also will use nest boxes that are on posts out in the water. The main benefit of boxes built over water (or in a dead tree out in a lake that has risen) is that this eliminates predators such as raccoons and cats. To help keep raccoons from climbing up to a nest box on land, the pole should have a large cone shaped metal barrier.
Building your own
It's fun and easy to build a nest box for wood ducks and hooded mergansers. They both will use the same kind of nest. The information above explains the "why" of some of the common design features. The internet has many good sources for actual plans. One of them is this page at the Audubon Society's site. They mention the use of wood chips as nesting material ... about that:
Wood ducks don't bring any materials (except down) into their nests. In the wild they use tree hollows that have crumbles of wood at the bottom from decay or woodpecker work. So in your nest box you should provide wood chips (small) or wood shavings. Never sawdust! It is too fine and will choke the ducklings. When hens are first investigating nests they kick and dig around. One year a hen kept trying the nest but never stayed and I noticed more than the usual wood dust via the camera. So I took the shavings out, removed the dust (read on), and put them back. Maybe coincidence, but she then settled in, so maybe she is checking for dangerous levels of dust. The easiest source for wood shavings is the pet store where you can buy compacted bags of gerbil/hamster bedding. Make sure it is pure wood without any colorings, deoderizers, or aromatics. You can remove any lingering dust by dropping handfuls of it into a bucket from chest-high, repeating as needed. Even a very slight breeze will carry the dust away.
The cameras in the wood duck nest boxes are made by Amcrest, model IP2M-841B. They are HD pan/tilt cameras, which is sometimes kind of nice in the nest boxes since I can pan them up to the doorway when the ducklings are jumping. I also set up one of these cameras outside the nest box on the day when the ducklings jump from the nest. Some of the video from outside and many of the still images are taken with a Panasonic DMC-FZ1000 camera.
For good focus I had to add "reading glasses" for the cameras as shown in the first photo above. I used plastic-lensed 2x (East) and 4x (West) reading glasses from the hardware store ($5 per pair), sawed out a little disk from the center of one lens, cut a shallow groove around it, then attached it to the camera's turret with wire and a couple of tiny screws. Without the added lens, objects are in-focus from about 2 feet out to infinity but in the nest boxes the ducks are closer than that. In the East nest box the camera is about 16 inches away and looks straight down: it's mounted upside down over a hole in the roof, pictures 2 and 3 above (it's a gallery that scrolls sideways). In the West nest box the camera is mounted sideways, looks in from the side, and is even closer, about 8 inches away (pictures 4, 5, and 6).
The cameras have infrared LED lights behind the black-looking ring (first picture), which is actually a very deep red color that is transparent to infrared. The lights turn on automatically when the camera senses that it's getting dark. Like us, the ducks cannot see infrared light, so they think it's dark in the nest box even when the lights are on. The turn-on of infrared also switches the camera to black-and-white mode since infrared light does not reveal color. This switching often occurs when the ducks enter and leave the nest too, since they sit in the doorway and block the light.
The cameras are set up to record a couple of minutes of video and audio onto a micro-SD card in the base whenever they see motion. That is particularly good in the early part of the nesting season when the ducks spend very little time in the nest box because it's easy to find and review the few minutes of actual activity. Apps from Amcrest allow viewing and control from both a computer and a phone.
The cameras are connected to line voltage power through the typical wall wart adapters, which for years has required outdoor extension cords that run from the house out to where the nest boxes are. However I now have buried low voltage wire to the cameras which makes mowing much easier. But that's the only cable requirement. The live video, camera setup and control, and recorded video playback all are done via WiFi. To give the cameras a good WiFi signal there's an outdoor wireless access point on the back of the house, dedicated to the cameras.
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The software used:
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The other site pages were developed using the Bootstrap web page blocks which come bundled with the Mobirise editor. Mobirise lives up to its reputation of being easy to use and is also very stable: it has never crashed, lost anything, or failed to behave as intended. I'm using the free version with none of the add-in features. To compensate for that just a bit, I've used a a Perl script to post-process the pages that Mobirise generates to alter some of the CSS formatting.
Both Wordpress and Bootstrap are nicely responsive to different user interfaces: desktop PCs, phones, and pads all work well.
Google's Chrome also deserves a mention since the web page developer tools within the browser are so well done.
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