a river or marsh . Both the male and female then set about to dig a horizontal tunnel into the bank , typically anywhere from three to six feet deep , an engineering project for which they are well adapted . Using their beaks as well as their two fused front toes ( syndactyl feet ) to excavate into the bank , they periodically kick dirt out of the tunnel with their feet and remove mud from their feathers with their beaks as they progress .
The resulting tunnel serves to protect the interior nest site from encroaching water in two ways . First , the birds situate their nests well above the conventional highest water level and , second , they slope the tunnel gradually upward from the entrance to the innermost nest area . This design not only removes the nest from the elements but also helps protect the young from predators , such as hawks . Despite this , persistent snakes , skunks , minks , and raccoons can still access eggs and chicks . With the pair working persistently , construction can take from one to three weeks to complete , creating tunnels so well-built that swallows have sometimes been known to use them by digging out rooms of their own . ( American Bird Conservancy 2019 )
Once the tunnel and nest are established , the male feeds the female , beginning about ten days before the female starts to lay her eggs and continuing until she lays her last egg , which can be up to another ten days . The typical clutch consists of five to eight eggs , and the sexes share brooding
duties for an incubation period of 22 to 24 days . Usually , these birds have only one brood per year , but they may have two clutches in warmer climates .
The energy demands intensify on both parents once the eggs hatch as they strive to respond to the cries for food from their clamoring chicks . Scientist William Davis found that a nursing pair needs to obtain ninety fish a day , each averaging four inches long , to feed their nestlings . ( as quoted in Line 1995 ) The male may put in more time performing this task than the female as her body recovers from the strain of egg-laying .
When it is time for the chicks to fledge , the parents curtail feeding in the nest and begin enticing the young out of the nest by holding a fish just outside the tunnel entrance . It takes about three weeks for the young to learn to fly and fish on their own . During this time , the offspring are vulnerable to certain predators , such as hawks , and the parents use aggressive territorial displays to defend their young .
Both sexes conduct this protective behavior throughout the entire nesting and breeding season . They can patrol a shoreline or stream up to 1,000 yards in length by using loud cries , raising their crests , and displaying the white patches next to each eye , all with the aim of intimidating trespassers , such as hawks , mammals , and snakes . Males maintain this display behavior throughout the entire year as they guard their feeding territory against interlopers .
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