We studied kleptoparasitism by Heerman's Gulls (L. heermanni ) on the piscivorous Brown Pelican (Pelecanus occidentalis ) in the Gulf of California, Mexico to answer two questions: (1) did adult or ...immature Heermann's Gulls differ in their frequency of kleptoparasitic attempts?, and (2) did Heermann's Gulls attempt to kleptoparasitize immature or adult Brown Pelicans more often? The study area was a 20 x 45 km section of the Canal de Ballenas.
Abstract
1. In mixed species flocks of lapwings and golden plovers, lapwing net rate of energy intake was positively related to the number of conspecifics and the amount of time individuals spent ...crouching during feeding, but was unaffected by the presence of golden plovers. Plover net rate of energy intake, however, was positively related to crouching tendency, negatively related to the number of lapwings present but unaffected by the number of conspecifics. 2. Golden plovers appeared to join lapwing flocks because they could then crouch more and scan less. The independent negative effect of lapwing number may have been due to feeding interference when there were large numbers of lapwings relative to plovers. 3. When black-headed gulls joined a flock, both lapwings and plovers tended to crouch less and take smaller worms. However, in lapwings these changes appeared to reduce feeding efficiency but plover net rate of energy intake increased as a function of the gull: plover ratio. 4. When gulls were present, the effect of conspecifics on lapwing feeding efficiency disappeared and the presence of plovers had a negative effect. Conversely, in plovers the presence of conspecifics enhanced feeding efficiency and the negative effect of lapwing number disappeared. 5. The arrival of gulls resulted in a decrease in equilibrium lapwing number but no consistent, directional change in plover number. When gulls were present, lapwing number tended to decrease when large numbers of plovers arrived, but increase when small numbers arrived. Increased lapwing number had no significant directional effect on plover number. Changes in lapwing and plover energy intake and species numbers are interpreted in terms of feeding interference and 'dilution' of gull kleptoparasitism. 6. In the absence of gulls, there was no significant directional relationship between increased plover number and lapwing number, but the presence of plovers generally correlated with a reduction in lapwing number. Plover number, however, decreased when large numbers of additional lapwings arrived but increased with small numbers of arrivals. Changes in species energy intake and numbers here are interpreted in terms of feeding interference and time budget changes.
Kleptoparasitism on other raptors was one means by which Bald Eagles (Haliaeetus leucocephalus) secured food along the North Platte and Platte rivers during the winters of 1978-1980. Species ...kelptoparasitized were Ferruginous Hawk (Buteo regalis), Red-tailed Hawk (B. jamaicensis), Rough-legged Hawk (B. lagopus), Golden Eagle (Aquila chrysaetos), and Bald Eagle. Stealing of prey occurred more often during the severe winter of 1978-1979 when ice cover restricted eagles from feeding on fish than during the milder winter of 1979-1980. Kleptoparasitism occurred principally in agricultural habitats where large numbers of Mallards (Anas platyrhynchos) were foraging. Subadults watched adults steal food and participated in food-stealing with adults, which indicated interspecific kleptoparasitism may be a learned behavior. We suggest factors that may favor interspecific kleptoparasitism as a foraging strategy of Bald Eagles in obtaining waterfowl during severe winters. /// El cleptoparasitismo a otras aves fué una de las formas en que aguilas calvas (Haliaeetus leucocephalus) pudieron obtener alimento a lo largo del Norte y rios del Platte durante los inviernos de 1978-1980. Víctimas de las aguilas calvas lo fueron Buteo regalis, B. jamaicensis, B. lagopus, Aguila chrysaetus y miembros de su propia especie. El robo de presas ocurrió más amenudo durante el invierno severo de 1978-1979, cuando el hielo sobre el agua restringió la pesca a las aguilas, que durante el invierno más cálido de 1979-1980. El cleptoparasitismo ocurrió principalmente en hábitats agrícolas, donde un gran número de patos (Anas platyrhynchos) se alimentaban. Aguilas subadultas que observaron a adultos robar alimento, luego participaban del cleptoparasitismo. Esto sugiere que esta forma de conseguir alimento es un patrón de conducta aprendido. En el trabajo se discuten factores que favorecen el cleptoparasitismo interespecífico como estrategia de forageo en aguilas calvas para obtener alimentos durante inviernos severos.
Kleptoparasitic attacks by adult and first winter (immature) black-headed gulls in flocks of lapwings (Vanellus vanellus) were compared. Attacks by immatures were less successful because they were ...more likely to be mistimed and detected by the target and immatures were apparently less selective in launching long distance attacks and choosing vantage points within flocks. As a result of their reduced success rate immature gulls tended to attack more often and were more likely to adopt other foraging techniques. There is some evidence that lapwings responded differentially to the arrival of adult and immature gulls. The success rate of attacks by immatures increased through the winter and immatures were correspondingly more likely to be encountered as kleptoparasites later in the season. Nevertheless success and intake rates among immatures did not increase to those among adults even by the end of the winter.
A list of Nearctic species of Miltogrammini and their associated species of Vespoidea, Pompiloidea, Sphecoidea, and Apoidea is presented. The list is based upon examination of late 19th and 20th ...century literature on the nesting behavior of solitary wasps and bees and current research of the authors.
