Defining the Melakha of Tzeida
The mishna (Shabbat 106a) lists several cases of capturing animals that violate the melakha of tzeida (capturing). Unlike classic melakhot, which create a discernible change upon an item, tzeida doesn’t create any change. The simple description of tzeida implies that no transformation occurs. By detaining an animal, the person has simply enabled further human utility. This is a human benefit, but in no way alters the subject of the animal. Why is this melakha forbidden if it deviates from the classic dynamics of melekhet Shabbat?
The mishna describes that capturing a bird is only forbidden if performed with a cage, but not within a larger structure. Adjusting this statement, the ensuing gemara states that the mishna is discussing a rowdy species of bird that rarely submits to human authority unless it is caged in extremely small confines. Typical birds, which are more submissive, may not be interned even in larger structures. This implies that tzeida is forbidden because it limits the freedom of the animal and thereby changes the state or condition of the captured animal. Accordingly, perhaps tzeida is indeed a conventional melakha, as it alters the state of freedom of the animal by imposing human control over it.
Said Otherwise: Is tzeida forbidden because it strips the animal’s freedom (in which case it resembles a classic melakha)? Or is the mere facilitating of human utility prohibited even without effecting a change upon the animal. A potential nafka mina would surround situations in which the animal's freedom were curtailed but human accessibility was not enhanced. Rashi (Chagiga 11a) defines the Biblically listed rodent of chomet as a snail. Since tzeida is forbidden for all Biblically listed rodents (see mishna, Shabbat 107), Rashi evidently maintains that capturing a snail would violate tzeida. Similarly, Rashi (Shabbat 107) claims that seizing a worm would violate tzeida. Finally, Rashi (Shabbat 106b) insinuates that capturing a fatigued deer who can hardly move would be forbidden. Evidently, in Rashi’s view, divesting animals of their freedom, even if the animal’s movement is limited to begin with, constitutes tzeida. By contrast, the Tosafot Rid (in Chagiga) argues that detaining a snail would not entail tzeida. Evidently, in his view, tzeida is only violated when human accessibility has been attained. Since a snail (or worm) is always attainable - as it moves so slowly - no tzeida act has occurred if it is “detained” on Shabbat. Rashi and the Tosafot Rid debate whether tzeida is defined as denying animal freedom or as enabling human utility and accessibility.
In fact, this issue may have been debated by both the Tanna’im and Amora’im. R. Yehuda and the Chakhamim (mishna, Shabbat 106a) debate whether confining a deer to a larger enclosed area (bibar) would violate tzeida, as the freedom of the animal has been curtailed. R. Yehuda asserts that tzeida is violated only when the animal is confined in smaller, house-sized quarters. Presumably, R. Yehuda envisions tzeida as enabling human accessibility. Since a deer cannot be easily captured when contained in a large enclosure, no tzeida has occurred. By contrast, the Chakhamim acknowledge tzeida violation even when confining a deer to an enclosure as its freedom has been deprived. (The Bach assumes this logic in the debate.)
There are two debates among Amora’im that may also reflect the debate about defining tzeida. Rav Ashi (Shabbat 106b) describes an area in which it is possible to grab a deer with one sustained attempt, without resting in between. Placing a deer into this enclosure would constitute tzeida violation. This suggests that tzeida is defined as placing an animal in a situation that facilitates relatively simple human access. Intriguingly, and consistent with his earlier comments, Rashi redefines this space, writing that tzeida is only violated if the animal is confined to an extremely small yard that allows capture with one thrust or grab. Since Rashi maintains that tzeida entails denial of animal freedom, it is violated only by placing an animal in a small enclosure that allows immediate detainment.
By contrast to Rav Ashi, Shmuel (Beitza 24a) claims that tzeida is only violated by placing an animal in an enclosure that allows detainment without employing trapping mechanisms. Many Rishonim view this measurement as disagreeing with the earlier measurement stated in the name of Rav Ashi (see the machloket between the Ran and Rashba in Beitza). Shmuel maintains that even if the animal is relatively free, tzeida been effected, since humans can now more easily apprehend the deer without the use of traps. It is clear that Shmuel defines tzeida very differently – as enabling human availability, even if it has relatively little impact upon the animal!
Finally, Elazar ben Mehavai (Shabbat 106b) claims that grabbing locusts during a massive swarm would not entail a tzeida violation. The apprehension of these swarming locusts is too “easy.” Simply by sweeping a net, or even your hand, you are bound to seize a few locusts. This resembles the case of the snails and worms, which are easily accessible before an act of tzeida and whose detainment therefore does not constitute tzeida. Human accessibility has not been advanced through the tzeida act.
Having defined tzeida as the removal of animal freedom, Rashi is left with two options in addressing Elazar ben Mehavai's position. He could claim that this is a minority opinion (as is implicit in the gemara). Elazar ben Mehavai did indeed define tzeida as acquiring human accessibility, and by extension exempted catching swarming locusts because they were always accessible. However, the Chakhamim claim (as does Rashi) that tzeida is violated any time animal movement is eliminated, and that capturing swarming locusts therefore entails tzeida.
Alternatively, Rashi may maintain that the concentration of swarming locusts prevents already “free-movement” by the locusts. This limitation may also be chemical and instinctive, and not just spatial. When locusts swarm, they are being driven to a common trajectory and movement by powerful instinct, and not simply by promise of readily available food. Since they aren’t "free" to determine their path, they do not enjoy freedom, and their capture therefore is not a tzeida violation.
The aforementioned cases describe situations in which freedom was removed but accessibility was not achieved, because it already pre-existed the tzeida (as in the case of slow-moving animals or swarming locusts). A related case involves a scenario in which freedom is limited but accessibility is not achieved because the animal can quickly flee. The Sefer Ha-Terumot (cited by the Shibbalei HaLeket 125) prohibits closing a box that contains flies. Arguing with the Terumot, the Tur claims that since the flies cannot be easily grabbed (as they will escape when the box is open), tzeida has not been violated. It is evident that the Terumot defined tzeida as denying freedom, whereas the Tur defined it as enabling human utility.
Another interesting exception to tzeida relates to birds that present predictable migratory patterns and are dependent upon humans for their food. The gemara in Beitza (24a) asserts that detaining these birds would not violate tzeida. The Tosafot Rid claims that since these birds can be “fully” controlled, their apprehension does not constitute tzeida. At night, they return to their coops, and even during the day they are forced to return for food. Since humans have continuous access, seizing them does not violate tzeida. This is consistent with the Tosafot Rid’s position exempting worms and snails from tzeida. If tzeida entails creating human accessibility, it does not apply when that accessibility pre-exists. For slow-moving animals, it exists because of their pace, and for these birds because of their behavioral patterns.
The Ran in Beitza explains this exception very differently. Since these birds return to sleep and are fed by humans, they are effectively domesticated, and their capture thus does not entail tzeida. Since tzeida entails imposing will upon animals, it would not apply to domesticated animals that already have embraced human authority. In theory, even if a domesticated animal’s movement were restricted, tzeida might not apply, since the restriction of movement does not reflect a new imposition of will on a broader scale. Domesticated animals have already submitted to human control and their capture does not represent imposition of human authority. By describing tzeida in this fashion, the Ran appears to agree that tzeida entails imposing human will on animals, rather than enabling human accessibility.
Finally, this question may help explain an interesting exception to tzeida – animals that are not typically hunted/captured (ein be-mino nitzod). This issue was debated by R. Meir and the Chakhamim (Shabbat 106b), as well as by R. Yehoshua and R. Eliezer (Shabbat 107b). On the surface, the exemption for animals that are not typically captured seems odd. The Avnei Nezer (189) claims that tzeida is the acquisition of human utility, and not the imposition of will upon the animal by restricting movement. If humans do not typically capture this animal, conventional human utility has not been enabled and no tzeida is violated. If tzeida consisted of imposing will upon an animal, it would make little difference from the animal's perspective whether humans typically capture it. Defining tzeida from a human vantage point and based on human norms can best be understood by defining tzeida as a process that yields (classic) human accessibility.