Role of Sibling Aggression in Food Distribution to Nestling Cattle Egrets (Bubulcus Ibis)
Role of Sibling Aggression in Food Distribution to Nestling Cattle Egrets (Bubulcus Ibis)
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兄弟姐妹攻击行为在雏鸟牛背鹭（Bubulcus Ibis）食物分配中的作用
DOI：
10.1093/auk/103.4.768
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
D. Mock
中科院分区：
文献类型：
--
作者：
Bonnie J. Ploger;D. Mock
兄弟姐妹a型进犯发生在各种各样的非同步孵化的鸟类中。在某些情况下，兄弟姐妹之间的权利不可避免地导致死亡，在这种情况下，获胜的好处是显而易见的。在兄弟姐妹攻击很常见但通常不致命的物种中，获胜所获得的好处和实现这些好处的方法不太明显。在德克萨斯州的一群牛白鹭（Bubulcus ibis）中，兄弟姐妹间的攻击经常发生，但兄弟姐妹间的残杀却很少见。父母很少干涉打架。最后孵出的小鸡比它们的哥哥姐妹们输掉了更多的战斗，得到的食物也更少。争斗限制了失败者立即获得食物的机会，并助长了年长的兄弟姐妹垄断奖金的能力。这些结果与假设一致，即垄断食物可以作为兄弟姐妹攻击的直接和最终原因。兄弟间的攻击主要影响在于减少最后孵化的雏鸟的食物供应。第一和第二孵化的兄弟姐妹积累了大致相等的喂养优势。1985年8月19日收到，1986年4月11日接受。许多猛禽、鹤、苍鹭和其他各种鸟类每隔一天或更长时间产卵，在产卵完成之前就开始孵化。这种模式产生了一个非同步孵化（Gibb 1950, Inoue 1985），其中最年轻的通常比它们的老同伴生长得更慢，因此更有可能在雏鸟中死亡（参见Lack 1954, 1968; Howe 1978； O'Connor 1978; Hahn 1981; Mock 1984a, 1985）。这些死亡可能是由于饥饿或兄弟姐妹施加的身体虐待（O'Connor 1978, Stinson 1979, Mock 1984a）。与其他非同步孵化的物种一样，牛白鹭（Bubulcus ibis）幼雏的生长速度通常比它们的同伴慢，而且更有可能在雏鸟中死亡（Blaker 1969, Siegfried 1972, Fujioka 1984， D. F. Werschkul unpubl）。数据)。虽然饥饿似乎是死亡的主要原因（Siegfried 1972），兄弟姐妹之间的争斗也可能导致死亡（Skead 1966; Blaker 1969; Siegfried 1972; Fujioka 1985, b; Werschkul unpubl）。数据)。兄弟姐妹打架的后果可能是直接的（受害者死于受伤）或间接的（受害者变得太害怕而不敢进食）。兄弟姐妹攻击对牛白鹭雏鸟生长和死亡率的间接影响•现在地址：佛罗里达大学动物学系，Gainesville, Florida 32611 USA。模式尚不清楚。我们试图估计牛白鹭兄弟姐妹之间攻击行为的利弊。通过创造非同步孵化，父母可以促进适应性的产卵减少，从而在面对不可预测的食物供应时最大化自己的繁殖产量（Lack 1947, 1954）。如果在食物短缺的情况下，最年轻的雏鸟的死亡增加了剩下的一窝成员的生存机会，那么兄弟姐妹之间竞争不对称的产生可以帮助最大限度地提高父母的繁殖成功率。当食物充足时，所有的雏鸟都有可能存活下来，但如果食物有限，最后孵化的兄弟姐妹可以被巢中的配偶有效地打发走。因此，父母可能会受益，因为他们幸存下来的后代获得了可能被注定要死去的兄弟姐妹拿走的食物。在许多鸟类物种中，兄弟姐妹的攻击并不需要减少后代数量，体型和年龄的差异足以迫使最小的兄弟姐妹挨饿（Lack 1954, 1968; Howe 1978; Werschkul 1979； Ryden和Bengsston 1980； Hahn 1981; Mock 1984a; Inoue 1985）。从理论上讲，依靠非攻击性繁殖的雏鸟可以避免与战斗相关的时间和精力成本（Hamilton 1964, Hahn 1981）。因此，为了使战斗具有优势，胜利者必须积累补偿性利益，例如增加获得有限食物的机会。Mock （1984b, 1985）提出当食物在monop768中递送时。《海洋科学》103:768-776。1986年10月1986年10月]牛白鹭的兄弟姐妹攻击769个可被猎杀的小单位，选择倾向于由年长的巢穴伴侣攻击年轻的兄弟姐妹。兄弟姐妹的攻击行为似乎在野猫中很普遍（参见布莱克1969年、米尔斯坦等人1970年、Werschkul 1979年、Fujioka 1985年b、Mock 1985年），但对其对有限食物分配的影响知之甚少。关于雏鸟攻击的优势的详细论证只在大白鹭（Casmerodius albus; Mock 1985）和日本牛白鹭种群（Fujioka 1984, 1985b）中有过。年长的大白鹭比年轻的兄弟姐妹获得更大的食物份额，通过(1)获得更频繁的食物来源（父母的喙），(2)获得更大的份量，(3)垄断更多的份量。大白鹭的幼崽也会吓到小白鹭，导致它们错过许多食物。本文研究了牛白鹭的种群内竞争。我们的工作与Fujioka （1985b）的描述性研究相似，该研究因不同的育雏规模和小样本量而变得复杂。我们使用单一的育雏规模，这允许更稳健的统计处理。我们通过调查攻击对喂食失败的频率和每只小鸡估计的食物消耗量的影响，为攻击如何影响兄弟姐妹之间的相对喂食成功提供了新的信息。我们提出的假设是，最小的两个兄弟姐妹之间的争斗最为激烈。这个想法是基于两个基本属性的育雏减少在异步孵化的鸟类。首先，最后孵化的个体死亡率不成比例地下降，其次，随着最初的孵化数量减少，剩余个体的死亡率风险下降（布莱克1969年，齐格弗里德1972年，藤冈1984年，Werschkul unpubl对牛白鹭的研究都有很好的记录）。数据;Werschkul（1979）、Mock和Parker（1986）在相关物种中也有发现。此外，偶尔的“优势逆转”，即在家族内部的线性等级制度中，一个年长的兄弟姐妹占据了最低的社会地位，在其他动物中也有观察到（Mock unpublic）。数据)。因为倒数第二的小企鹅可能最容易受到这种潜在的致命逆转的伤害，所以它可能会投入额外的努力来巩固自己的霸主地位。因此，我们预测最小的两个兄弟姐妹会发生不成比例的冲突。我们还预测，如果生存取决于避免最次要的位置，那么倒数第二个和最后一个孵化的小鸡之间的战斗应该比其他两个二对更激烈（更长，涉及更多的打击）。
--Sibling a gression occurs in a wide variety of asynchronously hatching bird species. In some, •ights among siblings lead inevitably to death, in which case the benefits of winning are •lear. In species where sibling aggression s common but usually not fatal, the benefits gained by winning and the methods used to achieve them are less obvious. In a Texas colony of Cattle Egrets (Bubulcus ibis), sibling aggression was frequent but siblicide rare. Parents rarely interfer•ed with fights. Last-hatched chicks lost more fights and received less food than their elder siblings. Fighting limited the losers' immediate access to food and contributed to the senior sib's ability to monopolize boluses. These results are consistent with the hypothesis that monopolizable food can act as both a proximate and ultimate cause of sibling aggression. The main effect of sibling aggression lay in depressing food supplies to last-hatched chicks. Firstand second-hatched sibs accrued roughly equal feeding advantages. Received 19 August 1985, accepted 11 April 1986. MANY raptors, cranes, herons, and various other birds lay their eggs at intervals of a day or more and commence incubation before laying is complete. This pattern produces an asynchronous hatch (Gibb 1950, Inoue 1985), wherein the youngest typically grow more slowly than their senior nest mates and consequently are more likely to die as nestlings (see reviews in Lack 1954, 1968; Howe 1978; O'Connor 1978; Hahn 1981; Mock 1984a, 1985). These deaths may be due to starvation or to physical abuse inflicted by siblings (reviews in O'Connor 1978, Stinson 1979, Mock 1984a). As in other asynchronously hatching species, the youngest members of a Cattle Egret (Bubulcus ibis) brood typically grow more slowly than their nest mates and are more likely to die as nestlings (Blaker 1969, Siegfried 1972, Fujioka 1984, D. F. Werschkul unpubl. data). Although starvation appears to be the primary cause of death (Siegfried 1972), fights among siblings can result in mortality (Skead 1966; Blaker 1969; Siegfried 1972; Fujioka 1985a, b; Werschkul unpubl. data). The consequences of sibling fights may be direct (the victim dies from injuries) or indirect (the victim becomes too intimidated to feed). The indirect effects of sibling aggression on Cattle Egret nestling growth and mortality • Present address: Department of Zoology, University of Florida, Gainesville, Florida 32611 USA. patterns remain unclear. We attempted to estimate the advantages and disadvantages of aggression among Cattle Egret siblings. By creating asynchronous hatching, parents may facilitate adaptive brood reduction and thereby maximize their own reproductive output in the face of unpredictable food supplies (Lack 1947, 1954). If death of the youngest nestling enhances the survival chances of remaining brood members during food shortages, then the creation of competitive asymmetries among siblings can help maximize parental reproductive success. When food is abundant, all chicks are likely to survive, but if food is limited, the last-hatched siblings can be dispatched efficiently by nest mates. Parents thus may benefit because their surviving offspring gain food that might have gone to the doomed sibs. In many avian species, sibling aggression is not required for brood reduction, size and age differences being sufficient to enforce the starvation of the smallest sibs (Lack 1954, 1968; Howe 1978; Werschkul 1979; Ryden and Bengsston 1980; Hahn 1981; Mock 1984a; Inoue 1985). Theoretically, chicks that rely on nonaggressive brood reduction could avoid the costs of time and energy associated with fighting (Hamilton 1964, Hahn 1981). Therefore, for fighting to be advantageous, victors must accrue compensatory benefits, such as enhanced access to limited food. Mock (1984b, 1985) proposed that when food is delivered in monop768 The Auk 103: 768-776. October 1986 October 1986] Sibling Aggression in Cattle Egrets 769 olizably small units, selection can favor assault on junior sibs by senior nest mates. Sibling aggression appears to be widespread among ardeids (see examples in Blaker 1969, Milstein et al. 1970, Werschkul 1979, Fujioka 1985b, Mock 1985), but little is known about its effects on the distribution of limited food. Detailed demonstrations of the advantages of nestling aggression have been presented only for Great Egrets (Casmerodius albus; Mock 1985) and for a Japanese population of Cattle Egrets (Fujioka 1984, 1985b). Great Egret senior nest mates obtain significantly larger shares of food than younger siblings by (1) gaining more frequent access to the food source (parent's bill), (2) obtaining larger bolus portions, and (3) monopolizing more boluses. Elder Great Egret chicks also intimidate junior sibs and cause them to miss many food offerings. We studied intrabrood competition in Cattle Egrets. Our work parallels Fujioka's (1985b) descriptive study, which was complicated by variable brood sizes and small sample sizes. We used a single brood size, which allowed more robust statistical treatments. We provide new information on how aggression affects the relative feeding success among sibs by investigating the effects of aggression on the frequency of failed feeding attempts and the estimated amounts of food consumed by each chick. We propose the hypothesis that fighting is most intense between the two youngest sibs. This idea is based on the two fundamental attributes of brood reduction in asynchronously hatching birds. First, mortality falls disproportionately on the last-hatched individual, and second, following initial brood reduction, mortality risks drop for the remaining individuals (both points well documented for Cattle Egrets by Blaker 1969, Siegfried 1972, Fujioka 1984, Werschkul unpubl. data; also shown in related species by Werschkul 1979, Mock and Parker 1986). Furthermore, occasional "dominance reversals," in which one of the senior sibs comes to occupy the lowest social position in the linear intrabrood hierarchy, have been observed in other ardeids (Mock unpubl. data). Because the penultimate chick may be most vulnerable to such potentially fatal reversals, it might be expected to invest extra effort in reinforcing its supremacy. Therefore, we predicted that a disproportionate amount of fighting would involve the two youngest sibs. We also predicted that if survival depends on avoiding the most subordinate position, then fights between the penultimate and last-hatched chicks should be more intense (longer, involving more blows) than those of the other two dyads.