We mentioned last week, since according to most Poskim a person only fulfills this mitzvah if he acquires the eggs, one should make every effort to take the chicks or eggs. However, in a situation that one finds more than one egg, he is not required to take all the eggs, he only needs to take one. Furthermore, in the above situation there is more than one egg, multiple people can perform the mitzvah; for example, one person should chase away the mother and take one egg. After the mother returns a second person should chase away the mother again and take a different egg, and so on (Sefer Sha'laiach Tishalach pg. 50 quoting Reb Y.S. Eliyashuv zt"l).
There is a machlokes as how one needs to send away the mother bird. According to Harav Y.S. Eliyashuv zt"l the only way to fulfill this mitzvah is to physically grab onto the mother bird. However many Poskim disagree and hold one may send her away using any method (Sefer Sha'laiach Tishalach pg. 40-41 quoting Chazon Ish [YD 175:2], Steipler Goan, Satmar Rov, Harav Shlomo Zalman Auerbach, Harav Shmuel Wosner zt"l and ybl"c Harav Moshe Sternbuch shlit"a). According to this latter opinion, one may use a broom or stick, throw a rock, spray with a hose or make a loud noise (Sefer Sha'laiach Tishalach pg. 76-77 quoting Harav Chaim Kanievsky shlit"a).
It is important to mention, many times when the mother bird senses danger, she will fly away. Therefore, upon approaching the nest one should have intention that he wants to fulfill the mitzvah, for even if the mother flies away before he scares her off, he will have nevertheless fulfilled this mitzvah (Sefer Sha'laiach Tishalach pg. 77 quoting Harav Chaim Kanievsky, shlit"a).
One only fulfills the mitzvah by sending away the mother and not the father (Shulchan Aruch YD 292:7). Nowadays it is fairly common that during the day time hours the father and the mother alternate sitting on the nest. During the night time [after sunset] only the mother sits on the nest. Therefore, in order to ensure that one is fulfilling the mitzvah, it is preferable to chase away the mother during the night time hours (Sefer Sha'laiach Tishalach pg. 51).
The Torah states "When you happen upon a birds nest". Chazal [Gemara Chullin 138b] explain what the Torah is teaching us is that if a nest was "prepared" there is no mitzvah to send away the mother (Shulchan Aruch YD 292:2). This means, that if someone owns the birds [e.g. he made a kinyan (halachic acquisition), one may not send away the mother. This lends itself to the following issue. A person's property has the ability to acquire something for its owner, even without the owner being aware (Shulchan Aruch CM
268:3 & Shach CM 268:3). Therefore, if a bird builds a nest on one's property, in many cases the owner has acquired the birds and may not chase away the mother. In order to be able to perform the mitzvah on nests that are in one's property, one may have in mind that he does not wish to acquire any birds that are on his property. (Igros Moshe YD 4:45:1).
There is a machlokes haposkim whether one may relinquish ownership on a nest that he already acquired in order to perform the mitzvah. According to Harav Y.S. Eliyashuv, zt"l, holds one may not, however Harav Moshe Feinstein, zt"l (Shu"T Igros Moshe YD 4:45:1) and ybl"c Harav Chaim Kanievsky, shlit"a, disagree that one may (Sefer Sha'laiach Tishalach pg. 64). According to this second opinion, even after one has fulfilled the mitzvah by sending away the mother and then acquiring the eggs, if he has in mind to renounce his ownership of the eggs, then additional people can fulfill the mitzvah with the same egg, since it is currently ownerless.