A kleptoparasitic spider, Argyrodes fissifrons, although it is much smaller, sometimes preys upon its host spider, Agelena limbata, during or just after molting of the host. I evaluated the impact of ...predation by A. fissifrons upon the host population in a woody field in Nagoya, Japan. A. fissifrons occurred on more than 75% of the host webs, but the percentage of hosts preyed upon by A. fissifrons was not high: 2% at the second molting, 3% at the third molting, 1% at the fourth molting, 4% at the fifth molting, 0% at the sixth molting, 8% at the seventh (final) molting. A. fissifrons preferentially preyed upon the host individuals whose development was delayed.
The stealing behavior of Argyrodes elevatus suggests that this kleptoparasitic spider monitors the movements and the hunting success of its web-building host. Wrapping of prey by the host regularly ...elicits raids from the kleptoparasite. The prey-catching activities of the host generate vibrations that were recorded with a position-sensing photodiode. The recordings indicated that wrapping movements produce a characteristic pattern of vibrations.
1. Flock size in lapwings correlated positively with the mean length of worm taken and birds in large flocks tended to take a more profitable mixture of worm sizes than those in small flocks. They ...also did better than expected on the basis of worm size mixtures in the ground. 2. Worm size taken was influenced by whether or not birds crouched before pecking. Crouching was associated with birds finding larger worms and taking predominantly the most profitable worm size classes. Crouching may have helped birds avoid broken fragments of worm common in feeding areas and small worms near the surface of the ground. 3. The proportion of pecks preceded by crouching increased significantly with flock size but decreased with the numbers of kleptoparasitic gulls in the flock. Perhaps as a consequence, lapwings tended to take smaller and, overall, less profitable mixtures of, worms in the presence of gulls. 4. The positive relationship between crouching and flock size appeared to be due to the relationship between flock size and worm density, birds feeding more selectively when searching costs were low. The negative relationship between crouching and the number of gulls, however, may have been due to lapwings reducing their risk of attack. /// 1. Die Schwarmgrösse von Kiebitzen (Vanellus vanellus) stand in positiver Wechselbeziehung zu der Durchschnittslänge der Würmer, die von den Vögeln aufgepickt wurden: Vögel in grossen Flügen pickten durchschnittlich eine vorteilhaftere Mischung von Wurmgrössen als diejenigen in kleinen Flügen auf. In Bezug auf die Wurmgrössenmischungen im Boden hatten sie auch einen grösseren Erfolg, als zu erwarten war. 2. Wir erkannten die Grösse der aufgepickten Würmer dadurch, dass die Vögel sich bückten, bevor sie pickten. Das Bücken wurde sowohl mit dem Erfolg, grössere Würmer zu finden als auch mit dem Aufpicken der überwiegend vorteilhafterer Wurmgrösseklassen verbunden. Das Bücken mag wohl den Vögeln geholfen haben, sowohl die in Futtergründen gelüufigen Wurmbruchstücke als auch kleine Würmer in Nähe der Bodenfläche zu vermeiden. 3. Der Anteil der Pickbewegungen nach dem Bücken nimmt mit der Grösse eines Fluges (Schwarmes) bezeichnend zu, aber sobald kleptoparasitische Lachmöwen (Larus ridibundus) im Flug anwesend sind nimmt dieser Anteil verhältnismässig ab. Vielleicht neigen Kiebitze dazu, in der Anwesendheit von Lachmöwen kleinere und im allgemeinen weniger vorteilhafte Wurmmischungen aufzupicken. 4. Das positive Verhältnis zwischen dem Bücken und der Fluggrösse schien auf das Verhältnis zwischen der Fluggrösse und der Wurmdichte zurückzuführen zu sein; die Vögel frassen offenbar wählerischer wenn die Suchekosten niedrig waren. Aber das negative Verhältnis zwischen dem Bücken und der Anzahl von Lachmöwen mag wohl darauf zurückzuführen gewesen sein, dass die Kiebitze das Risiko angegriffen zu werden reduzierten.
The spider Argyrodes antipodiana (O.P. Cambridge) from New Zealand is a kleptoparasite whose primary host in nature is an orb weaving spider, Aranea pustulosa (Walckenaer). The kleptoparasite's bias ...towards this host is stronger in the summer than in the winter. In the laboratory, Argyrodes was significantly better at obtaining food on the webs of Aranea pustulosa, than on the webs of Achaearanea sp., and Badumna longinquus (L. Koch). Factors that may be responsible for host preferences and for variation in efficiency on different types of webs are discussed.
Western Gulls (Larus occidentalis) at Bodega Bay, California drop shelled prey items to break them. I presented Washington clams (Saxidomus nuttalli) of known weight to free-flying gulls to ...investigate factors affecting shell-dropping behavior. All adult gulls dropped clams, whereas only 55% of immature gulls did so. The other 45% of immature gulls that were given clams pecked at them on the ground instead. Gulls dropped clams on both hard and soft substrates. Flight distance and kleptoparasitism seemed important in influencing drop location. Adult Western Gulls dropped heavy clams from lower heights than they dropped light clams. Heavy clams, however, break less easily than light clams when dropped from the same height. Energetic constraints and/or kleptoparasitism could explain this apparent contradiction.
Piracy (kleptoparasitism) accounted for 14% of observed foraging attempts on vertebrates (n = 125) by Aplomado Falcons (Falco femoralis) in southern Texas and northern Mexico, and was over twice as ...successful as hunting (82% versus 37%). Aplomado Falcons pirated prey cooperatively as well as individually. Eight bird species were targeted for piracy, six of which were as large or larger than the falcons. The majority of prey items stolen were mammals.
Based upon an analysis of patterns of variation in morphology, pigmentation, habitat, and Mysmenopsis kleptoparasites, two new species of Ischnothele from Jamaica (I. reggae and I. xera) are ...described. These allopatric sister species appear to have cospeciated with their respective Mysmenopsis kleptoparasite species, also each other's closest relatives. The rate of divergent evolution of the two kleptoparasite populations appears to be greater than that of the host populations, in part, we suggest, because of the kleptoparasites' shorter generation time.
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