Aggregation can reduce an individual’s predation risk, by decreasing predator hunting efficiency or displacing predation onto others. Here, we explore how the behaviors of predator and prey influence catch success and predation risk in Swainson’s hawks Buteo swainsoni attacking swarming Brazilian free-tailed bats Tadarida brasiliensis on emergence. Lone bats including stragglers have a high relative risk of predation, representing ~5% of the catch but ~0.2% of the population. Attacks on the column were no less successful than attacks on lone bats, so hunting efficiency is not decreased by group vigilance or confusion. Instead, lone bats were attacked disproportionately often, representing ~10% of all attacks. Swarming therefore displaces the burden of predation onto bats outside the column—whether as isolated wanderers not benefitting from dilution through attack abatement, or as peripheral stragglers suffering marginal predation and possible selfish herd effects. In contrast, the hawks’ catch success depended only on the attack maneuvers that they employed, with the odds of success being more than trebled in attacks involving a high-speed stoop or rolling grab. Most attacks involved one of these two maneuvers, which therefore represent alternative rather than complementary tactics. Hence, whereas a bat’s survival depends on maintaining column formation, a hawk’s success does not depend on attacking lone bats—even though their tendency to do so is sufficient to explain the adaptive benefits of their prey’s aggregation behavior. A hawk’s success instead depends on the flight maneuvers it deploys, including the high-speed stoop that is characteristic of many raptors.

中文翻译：

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鹰猎蝙蝠的空中攻击策略，以及集群的适应性优势

聚集可以通过降低捕食者狩猎效率或将捕食转移到其他人身上来降低个体的捕食风险。在这里，我们探讨了捕食者和猎物的行为如何影响 Swainson 鹰的捕食成功率和捕食风险Buteo swainsoni攻击蜂拥而至的巴西无尾蝙蝠Tadarida brasiliensis出现时。包括落伍者在内的孤独蝙蝠具有较高的捕食相对风险，占捕捞量的约 5%，但占种群的约 0.2%。攻击纵队的成功率不亚于攻击单独的蝙蝠，因此狩猎效率不会因群体的警惕或混乱而降低。相反，孤独的蝙蝠经常受到不成比例的攻击，约占所有攻击的 10%。因此，蜂拥而至将捕食的负担转移到了列外的蝙蝠身上——无论是孤立的流浪者，都没有从攻击减弱中受益，还是边缘的流浪者遭受边缘捕食和可能的自私羊群效应。相比之下，老鹰队的接球成功仅取决于他们采用的攻击策略，在涉及高速弯腰或滚动抓握的攻击中，成功的几率要高出三倍以上。大多数攻击都涉及这两种策略中的一种，因此代表了替代策略而不是互补策略。因此，虽然蝙蝠的生存取决于保持列队形成，但鹰的成功并不取决于攻击孤独的蝙蝠——尽管它们这样做的倾向足以解释它们的猎物聚集行为的适应性优势。相反，鹰的成功取决于它部署的飞行机动，包括许多猛禽特有的高速弯腰。鹰的成功并不取决于攻击孤独的蝙蝠——尽管它们这样做的倾向足以解释它们的猎物聚集行为的适应性优势。相反，鹰的成功取决于它部署的飞行机动，包括许多猛禽特有的高速弯腰。鹰的成功并不取决于攻击孤独的蝙蝠——尽管它们这样做的倾向足以解释它们的猎物聚集行为的适应性优势。相反，鹰的成功取决于它部署的飞行机动，包括许多猛禽特有的高速弯腰。