Sex and Breeding Status Affect Prey Composition of Harpy Eagles Harpia Harpyja
Total Page：16
File Type：pdf, Size：1020Kb
J Ornithol DOI 10.1007/s10336-017-1482-3 ORIGINAL ARTICLE Sex and breeding status affect prey composition of Harpy Eagles Harpia harpyja 1,2 2,3 2 Everton B. P. Miranda • Edwin Campbell-Thompson • Angel Muela • Fe´lix Herna´n Vargas2 Received: 31 December 2016 / Revised: 17 July 2017 / Accepted: 31 July 2017 Ó Dt. Ornithologen-Gesellschaft e.V. 2017 Abstract Foraging behavior may show considerable vari- than breeders. Our data provide support for the hypothesis ation among population classes—such as sex and breeding of parental role differentiation as an explanation for class—that can be consequence of the groups’ specific reversed sexual size dimorphism in raptors. constraints and roles. In raptors, differential parental roles related to foraging have been the main explanation for Keywords Reversed sexual size dimorphism Á Breeding males being smaller than females, as smaller males have constraints Á Role differentiation hypothesis Á Foraging Á been described to be more efficient foragers. During one Raptor Á Floater phase of breeding, only males forage, requiring them to feed themselves, females and young. This is expected to Zusammenfassung induce changes in foraging behavior of breeders compared to non-breeders. By comparing prey taken by floaters and Geschlecht und Brutstatus beeinflussen die breeders of Harpy Eagles (Harpia harpyja), we describe Beutezusammensetzung von Harpyien some effects of breeding and sex on the diet. Here we show that diet traits differed between male and female floaters, Das Verhalten bei der Nahrungssuche kann sich zwischen and between floaters and breeders. Juvenile prey was three den Populationsklassen—wie beispielweise Geschlecht times more common in the diet of males than that of und Brutklasse—betra¨chtlich unterscheiden, welches eine females. Sloths were more common prey among females Folge der spezifischen Beschra¨nkungen und Rollen dieser than among males (53 vs. 37%). Males preyed four times Gruppen sein kann. Bei Greifvo¨geln gelten die more on terrestrial animals than did females, and showed a unterschiedlichen Rollen der Elternvo¨gel bei der greater niche width than females (6.0 vs. 3.4). The prey of Nahrungssuche als die hauptsa¨chliche Erkla¨rung dafu¨r, breeders was smaller than that of non-breeders (on average dass die Ma¨nnchen kleiner sind als die Weibchen, da die 3.64 vs. 4.24 kg). Non-breeders had a larger niche width kleineren Ma¨nnchen als die effizienteren Ja¨ger gelten. Wa¨hrend eines Abschnitts des Brutgeschehens jagen nur die Ma¨nnchen, welche daher nicht nur sich selbst, sondern Communicated by O. Kru¨ger. auch noch die Weibchen und die Jungvo¨gel mit Nahrung ¨ Electronic supplementary material The online version of this versorgen mu¨ssen. Dies la¨sst Anderungen im Jagdverhalten article (doi:10.1007/s10336-017-1482-3) contains supplementary zwischen Brutvo¨geln und Nichtbru¨tern erwarten. Im material, which is available to authorized users. Vergleich von Beutetieren nicht-territorialer Harpyien (Harpia harpyja) mit denen von Brutvo¨geln beschreiben & Everton B. P. Miranda [email protected] wir einige Einflu¨sse von Brutstatus und Geschlecht auf die Nahrungszusammensetzung. Hier zeigen wir, dass sich die 1 ONF Brasil Gesta˜o Florestal, Cotriguac¸u, MT, Brazil Erna¨hrungsgewohnheiten nicht-territorialer Ma¨nnchen und 2 The Peregrine Fund, 5668 West Flying Hawk Lane, Boise, Weibchen sowie diejenigen der nicht-territorialen Vo¨gel ID 83709, USA und Brutvo¨gel unterscheiden. Im Nahrungsspektrum der 3 Fundacio´nA´ guilas de Los Andes, Pereira, Colombia Ma¨nnchen waren Jungtiere dreimal ha¨ufiger vertreten als in 123 J Ornithol dem der Weibchen. Faultiere wurden ha¨ufiger zur Beute mate for food (Schmutz et al. 2014; Sonerud et al. 2014). von Weibchen als von Ma¨nnchen (53% gegenu¨ber 37%). Therefore, during a key part of their life cycle, male raptors Ma¨nnchen erbeuteten viermal ha¨ufiger bodenlebende Tiere must be extraordinarily efficient foragers to feed them- als die Weibchen und wiesen eine gro¨ßere Nischenbreite selves, their mates and offspring. Their smaller size gives auf als diese (6,0 gegenu¨ber 3,4). Die Beutetiere der them more agility compared with females (Andersson and Brutvo¨gel waren kleiner als die der Nichtbru¨ter (im Schnitt Norberg 1981), and greater energy efficiency when carry- 3,64 kg gegenu¨ber 4,24 kg). Nichtbru¨ter nutzten eine ing heavy prey over long distances between foraging gro¨ßere Nischenbreite als Brutvo¨gel. Unsere Daten grounds and the nest (Hakkarainen et al. 1996). In the later unterstu¨tzen die Hypothese der elterlichen phase of nesting, when nestlings have acquired thermal Rollenverteilung als Erkla¨rung fu¨r den umgekehrten independence, the female reassumes hunting to recover her Gro¨ßendimorphismus bei Greifvo¨geln. depleted fat reserves, and shreds food hunted by her and by the male until nestlings are able to tear food themselves (Sonerud et al. 2014). Under these constraints, breeding raptors have to make important decisions between self- Introduction feeding or prey delivery; which kind and size of prey to hunt to maximize energetic gains from larger prey or to Ever since Darwin (1859), scientists have puzzled about hunt smaller prey to reduce carrying costs (Sonerud et al. why in many organisms males and females differ (Fisher 2013). These decisions are expected to affect foraging by 1930; Zahavi 1975). Indeed, sexual dimorphism is one of breeding raptors, when compared with non-breeding indi- the traits without which much of what is most extraordi- viduals free of these constraints—the floaters (Barrows nary, beautiful and bizarre in nature would not exist. 1987). Sexual size dimorphism has generated a still growing body RSD is pronounced in Harpy Eagles (Harpia harpyja). of knowledge on its origins and consequences (Catry et al. Males average 5.95 kg, and are 19% smaller than females 2016; Andersson 1994), given that body size is a key trait with a mean weight of 7.35 kg, resulting in a female:male driving organisms’ fitness (Mayer et al. 2016). In this linear body size ratio of 1.07 (n = 12, Peregrine Fund, unp. context, foraging behavior has become a focus of attention, data). Furthermore, the Harpy Eagle reproductive cycle is because it is highly affected by organism size. Foraging exceptionally long (Mun˜iz-Lo´pez et al. 2007), with an therefore offers a way of measuring the ecological and average of three years between each successful fledgling, evolutionary interplay that result in sexual size dimorphism which is expected to be highly demanding on males. Harpy (Angel et al. 2015). Eagle young depend on females to shred prey for them While most tetrapods show what is called ‘‘normal’’ until they are up to ten months of age, they fledge at six sexual size dimorphism—where males are larger than months and become independent at 2.5–3 years (Rettig females—in raptors (Accipitriformes, Falconiformes and 1978; Mun˜iz-Lo´pez et al. 2012). Harpy Eagles occur at low Strigiformes orders) larger females are the norm. This has densities (de Vargas-Gonza´lez and Vargas 2011), formerly been called ‘‘reversed’’ sexual dimorphism or RSD (Rey- throughout much of Central and South America. Threat- nolds 1972). Kru¨ger (2005) used comparative analyses to ened by habitat loss and shooting (Birdlife International test the three main hypotheses that have been proposed to 2016), range reduction is already impacting its genetic explain RSD in raptors: (a) niche partitioning—where size- diversity (Banhos et al. 2016). These problems drove The divergent sexes are able to reduce intersexual competition Peregrine Fund to test a restoration effort for the species, for prey; (b) role differentiation—where larger females are through captive breeding and reintroduction in their former better brooders and smaller males are better foragers and range (Watson et al. 2016). This kind of initiative is known territory defenders; (c) behavioral—where larger females to generate a great deal of information on foraging, since are dominant over males, aiding in the maintenance of the released animals require intensive monitoring (Hayward pair-bond and increasing male food-provisioning, or that et al. 2011). larger females compete more effectively for males. In this With respect to diet, the Harpy Eagle is the most studied synthesis, the better supported hypothesis was of role dif- of Neotropical raptors. While broad patterns on diet are ferentiation (b), mainly because small males seem to be known (Aguiar-Silva et al. 2014), important details are not. more efficient foragers. Nevertheless, raptor RSD is far The half century of systematic work on food habits—which from being a closed subject (Slagsvold and Sonerud 2007; resulted in more than 1000 identified prey items from fifty Olsen et al. 2013). nests—scarcely addressed food habits of floater eagles or In raptors, although males are smaller, they do most of differences between males and females. Touchton et al. the hunting during the initial breeding phase when the (2002) offered what may be the best piece of knowledge females are incubating and brooding and relying on their about Harpy Eagle foraging published to date. Despite 123 J Ornithol tantalizing evidence for differential foraging strategies by where there are effects of neither ontogeny nor experience male vs. female Harpy Eagles in Touchton et al. (2002), the in diet (Electronic Supplementary Material Fig. 1 and 2). small sample size (two individuals) allowed limited infer- We therefore consider foraging by reintroduced Harpy ence over the subjects discussed