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Cleaning and checking the backyard, front yard, or porch for Chametz?
The open areas: One does not need to search the open areas of his outside property for Chametz. This applies even if one knows for certain that there is Chametz outside. Furthermore, one may even Lechatchilah throw Chametz onto his outside property before the 6th hour on Erev Pesach. However, if one knows for certain that there was Chametz outside, then he needs to go outside when the 6th hour on Erev Pesach arrives, to check if there is any Chametz remaining, and if he sees any Chametz, he is obligated to immediately destroy it from the world.
One does not need to search at night the open areas of his outside property for Chametz, as all the Chametz has already been eaten by birds. However, closed items that are outside, such as boxes and one’s barbecue have to be checked. As well, if one knows for certain that there was Chametz outside, then he needs to go outside by the 6th hour on Erev Pesach to check if there is any Chametz remaining
 Admur 433:28
 The reason: As all Chametz that is found outside in the open is usually eaten by birds. The reason why we do not also exempt the entire house from being checked being that there are mice, rodents and the like found in one’s home which also eat Chametz, and although their eating is a doubt and thus cannot remove the certainty of Chametz, as explained above, nevertheless they certainly do take the Chametz to wherever they came from, as do the birds, and thus we should also exempt the entire house as we exempt the outside. The difference however is that birds are usually not domestic animals which live in ones property, and thus when they come from the outside and take the Chametz they certainly are removing it to the place that they came from, while rodents and mice live in one’s home, and thus even if they remove the Chametz we are stringent regarding a case of when there is Chametz for certain, that they dragged it to their hiding place within the house or courtyard of which one transgresses Baal Yimatzeh. [Admur ibid]
 Admur ibid; Rama 433:6
The reason: Although when the 6th hour arrives, he must go to his outside property to check if the Chametz is still there, and if it is there, not having been eaten by the birds/ravens, then as soon as he sees the Chametz he is obligated to immediately destroy it completely from the world, nevertheless, we allow one to place his Chametz there before the 6th hour. The reason for this is because even if one forgets to check his outside property by the 6th hour, nevertheless, he has not transgressed anything, being that we are certain that before the 6th hour the ravens have taken the Chametz and brought it to wherever they came from [and there is thus no more Chametz remaining outside]. Now, although we explained above that if there is only a doubt if the Chametz was removed then it does not uproot the status of the Chametz in a case that the we know for certain that there is Chametz there, nevertheless here it does uproot the status of Chametz, being that although there is doubt as to whether the birds ate the Chametz, as perhaps they were not hungry at that time, nevertheless it is certain that they have taken the Chametz to wherever they came from. Nevertheless, lechatchilah one should not rely on this when the time of destroying the Chametz arrives, at the 6th hour, as since one is able to go check if there is any Chametz still remaining outside, then let him go and see. [Admur ibid]
Other opinions: Some Poskim rule that when one knows for certain that there is Chametz outside, then he may not rely on the birds and must gather it on the night of the 14th. [Michaber 433:6; See Kinyan Torah 3:83]
 The reason: Lechatchilah when the time of destroying the Chametz arrives at the 6th hour, one should not rely on the fact the Chametz was taken by birds, as since one is able to go check if there is any Chametz still remaining outside, then let him go and see. [Admur ibid]
 Admur 433:29 “The holes in the walls of the outside property need to be checked if they are not too low or high, if it is usual for one to use the holes, as the ravens are not commonly found by the holes.”
 The reason: As since they are closed the birds do not have access to them. [Admur ibid]