The A-B-C’s of Nest Searching - How It’s Done and Why It’s Important

Editor’s Note: Most Delta Waterfowl members have heard about nest dragging, or as Liz Loos prefers to call it, nest searching. But exactly what is nest searching, and why is it so important?  This fascinating article shows the process in detail, and explains why it’s so important.

By Dr. Frank Rohwer, Scientific Director and Dr. Elizabeth Loos, Research Director

Duck biology isn’t rocket science.  From the hunter’s perspective, it’s about this simple:  Ducks that don’t hatch don’t migrate, don’t visit decoys and don’t wind up swimming in gumbo.

That’s why scientists spend so much time studying nest success. Nest success—the percentage of nests that produce at least one egg—is one of the most important factors determining duck populations.  Most scientists agree that 15 to 20 percent nest success is necessary to maintain the existing population. If nest success falls below that level, it’s important to find out why, and take steps to correct the problem.

Methods to elevate nest success vary and have led to rather heated debates.  That drama isn’t our focus; rather we are going to talk about what is sometimes referred to as “nest dragging”.  That doesn’t mean we find a nest and drag it around.  When we “duck nerds” say we are nest dragging or nest searching, we simply mean locating duck nests to monitor, usually to estimate local hatch rates.

Biologists define a successful nest as one that hatches one or more eggs.  Ducks often lay 10 or more eggs in their nest, so your first thought may be that hatching only one egg isn’t really very successful.  That’s true, but the key is that at least some eggs hatch.  Most duck nests on the prairies never hatch even one egg. 

Nests fail primarily because a predator finds the nest and eats the eggs.  Worse yet, predators like red fox also capture the female on the nest.  Nests can and do fail from causes other than predators, such as flooding, farm operations, or female abandonment for unknown reasons.

To measure nest success, biologists have to find a bunch of duck nests and then monitor those nests to determine their fate.  Nest searching is the key first step, and perhaps the most time-consuming.  Methods of finding duck nests vary. In some cases the process is a simple as checking established Hen Houses or wood duck nest boxes to see if a female is using the structure.  But for most upland-nesting ducks, the job involves a lot more work. 

Prairie ducks typically nest in two different places.  Teal, gadwall, pintail, mallards, and lesser scaup nest in grasslands.  We call these upland-nesting ducks because they nest in dry grassy areas.  Divers like redheads, canvasbacks and ruddy ducks weave their nests together out of the cattails or rushes that fringe most prairie wetlands.  These nests are almost always built above inches to feet of water, hence the term “over-water nesters.”

Finding nests for mallards and other upland nesters involves making a commotion that scares females enough to make them flush from their nest site.  (Male prairie ducks never sit at the nest; hens have sole responsibility in incubating the eggs and rearing the young.)  Typically, the disturbance needed to make hens flush and reveal their nest site is caused by dragging something through cover that is likely to have nests, hence the origin of that crazy term “nest dragging.”

Usually a chain is dragged through the grass, but that can vary.  The key is to cause enough of a disturbance to make the hen flush from her nest.  Most field crews searching for upland nests today use two all-terrain vehicles to drag a chain 100 to 300 feet in length stretched between them through the vegetation. Each link can be as small as 3/16-inch in diameter (the size of backyard swing set chain) or as heavy as 3/8-inch diameter (the size of a log chain).  The chain bounces over the grassland cover and causes enough of a disturbance to make most females flush from their nest.

When the hen flushes, biologists to hit the brakes and walk back to where the female flew out of the cover and look for the nest.  If the field crew has a good mark, then the painstaking business of parting the vegetation and finding the nest bowl with eggs may only take a minute.  If the crew did not get a good mark, the search for the nest can take a lot more time.

Be Careful Where You Step

Most veteran nest-searchers have probably experienced the agony on finding the nest with the bottom of their foot.  It is an awful crunch when your boot cracks one or more eggs in a hen’s nest.  Few biologists have to hear that terrible sound more than once before they exhibit extreme care in where they step.

It takes a little practice to get used to driving a vehicle while looking backwards at the chain rather than the direction you are driving.  Good nest searchers mostly drive their ATV with peripheral vision.  Sure, we occasionally hit a big rock or fence post, but good ATVs are tough, and most nest searchers are healthy young students. 

Novices always ask: “Doesn’t the chain hurt the eggs?”  The chain actually slides and  bounces over the vegetation several inches to a foot or more above the nest and eggs. 

Hens build their nests on the ground, usually in a depression we call a scrape.  The hen actually uses her feet to scrape down to the bare soil and lines with vegetation she can reach with her bill from the nest site. 

Nest-Building

One of the rituals of spring is watching songbirds carry twigs, string or feathers to their nest.  But you will never see a mallard hen fly with grass in her bill.  The grass that lines the bottom of a duck nest comes from what the hen can reach while standing on her nest.  A few days before a hen lays her last egg, she begins to pluck down and feathers from her breast to form the top layer of insulation and protective cover for her nest.  When a hen leaves her nest to feed, she will cover her nest with this mix of feathers, down, and grass.   (After biologists check a nest, they always re-cover the eggs with down to protect the nest until the hen returns.)

Hens are reluctant to flush from their nest, so the chain goes right over some females and they simply don’t fly.  Green-winged teal and blue-winged teal are notorious for not flushing when the chain goes over them.  If these females are more than halfway through their incubation stage—teal incubate for 24 days after laying their last egg—they are prone to sit tight and not flush.  Mallards and pintails, on the other hand, typically flush even late in incubation.

Nest searching sounds like fun.  It is always exciting to find nests, but spending eight hours on an ATV riding through fields with badger holes, and ant and gopher mounds makes your kidneys and back pretty sore.  The job is a lot more fun if you are finding a lot of duck nests, which is usually the case when we nest search on one of Delta’s trapped blocks.  In some places, however, you can nest search all day and only find a few nests, and when that happens nest searching seems like a real job.

Once a nest is found, we note the location on a map and put up some sort of visual marker at the nest.  Most of the time we put something subtle right at the nest, like a willow twig or a thin metal rod that blends with the grass, with a more obvious marker about 10 to 15 yards away from the nest. 

At Delta, we typically use a 4-foot flat wooden stake that has a unique number for each nest.  We put the stake some distance from the nest so that cleaver predators like foxes or crows won’t use the marker to help themselves to eggs for breakfast.  At intervals of a week to 10 days we then check each nest to determine if it has survived the period or been destroyed or abandoned. 

‘Candling Eggs’

We record all the basic nest information before we get back on the ATVs.  The number of eggs in the nest is always of interest.  For some studies, we might even measure the size or the weight of the eggs.  The other bit of information that all nest searchers record is the stage of incubation.  To divine that information we resort to what is called “field candling.”  This involves using a “radiator hose field scope” to look through one of the eggs in the nest. 

It sounds and looks bizarre, but by looking through the black hose the only light that gets to the eye has to pass through the egg.  If it is normal sunny day, this light allows us to actually see the chick that is developing inside the egg shell. 

Someone who has candled a lot of eggs can get close to the exact incubation day of the 23- to 26-day incubation period of prairie ducks.  Knowing the stage of development is important for calculating nest success and for predicting the expected date of hatch for that nest.

We continue the nest checks until we know the final fate of the nest: Destroyed by predators in most cases, hatched in most others.  Abandonment is quite rare, as are the other fates mentioned earlier. 

Duck biologists can tell if eggs hatched or were destroyed by a predator with careful examination of the nest.  Lots of tiny egg shell fragments are also a tell-tale sign the eggs hatched.  That’s because egg membrane separates from the egg shell when the duckling is hatching.  Egg shells get broken in lots of tiny little pieces and the nesting material is tamped down because the hen will stay on the nest with the ducklings for about 24 hours after hatch.

Remains of eggs eaten by predators look very different.  A skunk or raccoon will often eat the contents of the eggs right at the nest, leaving behind egg shells with big holes in them.  Badgers will often dig up the nesting material and eat the eggs, leaving a messy nest and pieces of egg shell behind. Red fox will often take all the eggs without disturbing the nesting material much, and a close examination of the nest reveals that there are no egg membranes or tiny shell fragments. 

So far we have described nest searching for ducks that nest in the uplands.  The efficient way to find such nests is by having the females tell you where their nests are by flushing from the cover.  In most instances, upland nests are spaced too far apart and are so well concealed they’re difficult to locate just by looking walking through fields. 

On the prairies we do the same thing for ducks that nest over water in the cattails and other emergent vegetation.  Canvasbacks, redheads and ruddy ducks build nests by weaving a platform of vegetation in a particularly thick patch of cover.  When those hens hear trouble coming they simply slip off the nest and subtly swim away.  There is no telltale flush of the hen to signal her nest. 

The best way to find canvasback nests is to muscle through the cattail like a coursing bird dog.  Each zig and zag is only five feet from the last path through the thick cover to assure that you don’t overlook one of these well concealed nests. 

Over-water nest searching is pure hard work that could be compared to an August training camp for football players.  Few people can take an eight-hour day of busting through thick cattails in waist deep water.  Unfortunately, the rewards are also few.  A good day for an over-water team of two is a handful of nests, while an ATV team in good upland habitat can rack up 50 or more nests.  It is no surprise that we know a lot more about mallards than cans and redheads.

Duck Voyeurism

“Duck voyeurism” is our favorite way to find upland duck nests.  A duck voyeur spies on ducks until the unsuspecting hen reveals her nest by flying to it.  It’s a tedious job because observers have to sit around watching hens in ponds, waiting for one to fly to her nest.  In areas of low nest density, voyeurism can be a faster way to find nests than aimlessly bumbling through cover on a couple of ATVs. 

Understanding the subtle body language cues of nesting hens makes the job easier. Incubating females leave their nests two or three times each day to get a drink, eat and have a bath.  A hen is only away from her nest for an hour or two, so she has a lot to get done.  If you see a female that looks busy—eating, drinking and bathing in rapid succession—park your truck and watch her for a while.   

It is great fun to find a nest by watching a hen drop into the cover.  Be alert as you watch the hen.  In most cases her paired male will be in her company.  The two ducks will fly out over the cover, the hen dropping into the grass and the male looping back to the pond.  If you aren’t careful, you can miss marking the spot where the hen landed near her nest.  In a high density duck-nesting area, being a duck voyeur is an inefficient way to find nests, but it is strangely fun to watch a hen fly to her nest.