attack his children in their room, and Nat kills over fifty of the birds, using a blanket as a defense weapon. Following this experience, he determines to protect his family from any further attacks by boarding up the windows and chimneys in his house as has been advised in the news broadcasts. After the second bird attack, he piles up his sills with bodies of dead birds for extra security. He also boards up his kitchen door. He notices that the “birds attack with the flood tide,” so he replenishes his family’s stock of food, fuel, and light from the Triggs’ farm.

Another theme is the role of women in the family. Throughout the story, Nat’s wife is portrayed as a weak person, someone to be taken care of, much like the children. Nat hides various important things from his wife—for instance, the fact that the birds have already broken into the children’s room upstairs, or that the Triggs are dead. Also, he does all the work that involves securing the house against attack from the birds, without any help from her. She mostly concerns herself with cooking, cleaning, and nursing her family’s injuries. This is one reason why Nat seems quite isolated in his fight against the birds toward the end of the story. It seems like it is him alone against the birds. Still, Nat’s family is unified in its struggle for survival, even if some of its members only play small roles in this struggle. Nat comes across as a strong leader and head of the family.

One theme is Daphne DuMaurier's story, "The Birds," is survival of the fittest. Nat Hocken is a survivor. Unlike the Trigg family, Nat instinctively feels that something is wrong with the birds from the very onset of the story. It is simply not usual for birds to attempt to gain entry into houses and attack people. After the first night of the attack by the birds, Nat listens to the news and begins to board up his house; Mr. Trigg does nothing except get ready "to join the shooting match." His plan is to shoot the birds and have fun while he's at it.

However, by the end of the story, the Triggs are dead. They didn't heed the advice of others. Nat protects his family by securing his house and getting the necessary supplies from the Triggs' farm. He and his family are able to survive the bizarre bird attack because he prepared for the worst. He is a survivor.

In "The Birds," one of the most prevalent themes is that of human survival; this is evident through the activities of Nat Hocken. In his efforts to keep his family safe from the birds, for example, Nat develops a number of survival tactics which range from physically battling the birds to maintaining supplies and improving the defenses of his home.

As the story progresses, Du Maurier introduces the theme of isolation. This is best depicted by the silence of the radio after only two broadcasts. These broadcasts are important because they provide the Hocken family with information and help them to feel connected to the rest of the world. The absence of these broadcasts, therefore, leaves the Hockens feeling isolated and totally dependent on themselves, as Nat comments:

“There isn’t going to be any news,” said Nat. “We’ve got to depend upon ourselves.”

Finally, it is also worth noting the theme of outsiders. This is demonstrated through the references to Russia, a country which is blamed by Mrs Trigg for the sudden change in weather. Later, the Russians are also blamed for the birds' attacks on humans. 

For more themes, please see the reference link provided.

I would say that one of the primary messages of Du Maurier's work is to underscore the fundamental capacity to endure and to survive as one of the basic characteristics of humanity.  The birds seek to attack and obliterate the humans.  Through Nat Hocken, Du Maurier suggests that one of the defining elements of human beings is the ability to persevere, try to care for what is important, and be prepared to prevent or offset the next attack.  Hocken never relents in protecting his family and ensuring that the birds are not successful in their onslaught against the human beings.  Hocken wishes that he could have helped more, but recognizes that he must protect himself and his loved ones against a formidable and relenting opponent.  It is in this where the primary message of the story resides.  Du Maurier understands the context in which she writes.  In the Cold War, human beings were constantly under siege from the threat of nuclear attack.  There is little in Hocken that suggests a weakness or capitulation.  He always prepares for the next attack, fighting through it with the best of his capacity.  In this, Du Maurier is highlighting what she considers to be one of the most intrinsic elements of being human and in this, adaptability and endurance can lead way to eventual triumph.  Regardless of what happens to Nat, the reader recognizes that his will to survive is what makes him human and makes the human spirit and indomitable one.

A definition paragraph is often part of first paragraph, the introductory paragraph, of an essay. It is an explanation of terms in the essay, or the topic of the essay. This can be accomplished through the use of synonyms, explaining which class the topic falls, and an explanation of what the topic is not.

With respect to "The Birds," a definition paragraph can, for example, explicate the du Maurier narrative as a gothic tale [See --http://www.virtualsalt.com/gothic.htm] The thesis, then, that comes at the end of the introductory paragraph will be a general statement of how these gothic elements presents work toward the development of the plot or of the theme. 

A descriptive paragraph is a paragraph that creates for the reader a sensory image of whatever is being described. It is important to be detailed and create a single impression with this paragraph. Thus, in writing a descriptive paragraph as part of an essay on "The Birds," the student may wish to use this paragraph as support for the thesis that du Maurier's tale is gothic. For instance, in an explanation of the horror and danger, the descriptive paragraph can point to the psychological horror of birds as destroyers, detailing incidents from the narrative, such as the following:

They were not intent upon their flight, as the crows, as the jackdaws had been. They still circled overhead. Nor did they fly so high. It was as though they waited upon some signal. As Though some decision had yet to be given. The order was not clear.

In this paragraph, the oddity of the birds' behavior as well as the suspense of what they will do indicates the unnaturalness of their behavior, the beginning of the psychological horror.