Question: May one move domesticated birds that live in a cage on Shabbat in order to move the cage from place to place as necessary? Similarly, may one remove a dead fish from one’s aquarium on Shabbat?
Answer: The Gemara (Shabbat 128b) states that it is forbidden to move or carry any animals or birds on Shabbat and they retain the law of other forms of Muktzeh on Shabbat which may not be moved.
Rabbeinu Nissim writes that the reason why animals are considered Muktzeh and forbidden to be moved on Shabbat is because animals are not able to be used for any purpose on Shabbat and thus, they retain the same law as wood and stones which are considered innately Muktzeh because they have no purpose on Shabbat. The Bet Yosef (Chapter 308) writes accordingly.
The same law applies to caged birds and since the birds themselves do not serve any purpose on Shabbat, they may not be moved, even when they are still in the cage. There is no distinction between moving animals or moving birds, as Maran Ha’Shulchan Aruch (Chapter 308, Section 39) rules, “It is forbidden to move any animals or birds on Shabbat.”
Nevertheless, Rabbeinu Chaim Ohr Zarua (one of the great Rishonim) rules that one may be lenient and move birds on Shabbat since people enjoy their voices on Shabbat and this enjoyment entails no prohibition. There is likewise no issue to move them, for they are not used for any type of forbidden work as people merely enjoy their appearance, voice, and chirping. Thus, according to Rabbeinu Chaim Ohr Zarua, caged birds may be moved on Shabbat. Nevertheless, halachically speaking, we follow the opinion of the Rosh and Maran Ha’Shulchan Aruch who rule that no animals or birds may be moved on Shabbat.
Maran Rabbeinu Ovadia Yosef zt”l writes (Volume 5 of Responsa Yabia Omer, Chapter 26) that although we rule in accordance with the Rosh that birds may not be moved on Shabbat, nevertheless, in a situation where the animal is suffering, such as if the cage is in a place where the sun is beating down on it or if it is in a very cold place and this poses danger and great suffering to the birds, one may rely on the opinion of Rabbeinu Chaim Ohr Zarua and move the cage to a shaded place. Maran proceeds to support his opinion with various proofs.
The same applies to tropical fish and when the fish are in a small aquarium and one fish dies, this poses a danger to the rest of the fish since the dead fish decomposes in the water, one may remove the dead fish on Shabbat although it is Muktzeh. This is because of the issue of animal suffering, as we have explained.
Summary: It is forbidden to move animals on Shabbat. It is therefore forbidden to move a bird cage on Shabbat. Nevertheless, in a situation where the birds are suffering, such as if the sun is beating down on the birds’ heads and this can cause them to die sometimes as well, it will be permissible to move the bird cage to a shaded place.