FAUNA PARAGUAY BELLBIRD JOURNAL AGGRESSION IN GREAT KISKADEES

The Great Kiskadee (Pitangus sulphuratus) is one of the commonest and most conspicuous bird species in Paraguay (del Castillo & Clay 2004, Smith & Clay in press) and is well known for its robust and rowdy nature. During fieldwork at Estancia Laguna Blanca, Departamento de San Pedro, Paraguay in November 2005 I made intermittent observations of three Great Kiskadee nests and noted some remarkable aggressive behaviour by their occupants.
The three nests were located within 400 m of each other on the southern shore of Laguna Blanca. All were similarly untidy structures with rounded, domed entrances set in tree forks (Fig. 1) and resembled those described in the literature (Narosky & Salvador 1998; de la Peña 1987, Fitzpatrick 2004). Incubating birds were clearly visible in the entrance of the nests and when approached closely would exit suddenly and noisily, flying to a nearby perch and calling loudly. They made no attempt to mob or dissuade observers from inspecting the contents of the nests and returned shortly after the nest inspection was completed.

In contrast to their relatively passive reaction to human observers, the kiskadees responded aggressively to the close proximity of large birds, even those that would not normally be considered a threat to the nest or its contents. This is a behavioural similarity with the related Tropical Kingbird (Tyrannus melancholicus) a quarrelsome species reported by Sick (1993) to “attack any bird…overflying its territory”; though the mobbing behaviour I observed in kiskadees was aimed only at birds larger than themselves and smaller birds provoked no reaction. Pairs of kiskadees were observed to aggressively mob Turkey (Cathartes aura) and Lesser Yellow-headed Vulture (C. burrovianus), Southern Lapwing (Vanellus chilensis), and White-backed Stilt (Himantopus melanurus). Kiskadees mobbed passing Giant Cowbirds (Molothrus oryzivorus) on several occasions, but other, smaller, more abundant nest parasites such as Screaming (M. rufaxillaris) and Shiny Cowbird (M. bonariensis) produced no aggressive response. Shiny Cowbird is a known parasite of Great Kiskadee (Fitzpatrick 2004) but Giant Cowbird is an obligate parasite of other Icterids (Sick 1993) suggesting that it was the mere size of the larger bird that triggered the mobbing behaviour rather than any potential parasitic threat it may have posed to the kiskadee nest.

The most dramatic mobbing reaction was to a passing Toco Toucan (Ramphastos toco), a known nest predator (Short & Horne 2001). Sick (1993) reported a Red-breasted Toucan (Ramphastos dicolorus) in Espirito Santo, Brazil, tearing apart a Kiskadee nest and devouring a fledgling, while Toco Toucans have been documented raiding colonies of Yellow-rumped Caciques (Cacicus cela) to plunder the contents of their nests (Short & Horne 2001). The sitting kiskadee reacted rapidly to the toucan as it flew by, darting out of the nest and chasing it whilst calling loudly ki-ko-weh, encouraging its mate to join the pursuit. The pair of kiskadees rapidly caught up with the toucan and held onto the tail of the larger bird with their bills, still calling but in a more muted manner. The toucan responded by angrily calling kronk-kronk

and was almost grounded by the extra weight. Just before impact, and presumably a safe distance from the nest, the two kiskadees released the toucan’s tail and peeled off back towards their nest. The toucan, which had by this time entered another kiskadee territory, was then accosted by the second pair until it disappeared from sight.
A third nest was located in a nearly leafless tree adjacent to and within 5 m of a small Butea palm. The palm contained the nest of a pair of Ruddy Ground-Dove (Columbina talpacoti), a simple stick structure wedged into the base of the palm fronds, and that of a pair of Social Flycatchers (Myiozetetes similis) a vase-shaped structure with a rounded, tubular entrance set lengthways along a palm frond from near the base to about halfway along its length (Fig. 2). The habit of Kiskadees nesting close to Myiozetetes flycatchers has been previously documented (Fitzpatrick 2004) and a pair of kiskadees with young in Brazil were even seen to feed the young of the smaller flycatcher (Sick 1993). Despite their proximity and similarities in plumage my observations revealed considerable antagonism between the two species. Each time a bird of either species arrived at the nest, the sitting bird of the other species would fly aggressively from its nest, mobbing it briefly and noisily before returning to the task of incubation. Neither the kiskadees nor the flycatchers showed any aggressive reactions towards the Ruddy Ground-Doves during nest changeovers.

References
1.de la Peña, M. R. 1987. Nidos y Huevos de Aves Argentinas. de la Peña. Buenos Aires.
2.del Castillo, H. & R. P. Clay. 2004. Lista Comentada de las Aves de Paraguay. Guyra. Paraguay.
3.Fitzpatrick, J. W. 2004. Family Tyrannidae (Tyrant-Flycatchers). Pp. 170-463 en: del Hoyo, J., Elliott, A. & Christie, D. A. eds. (2004). Handbook of the Birds of the World. Vol. 9. Cotingas to Pitpits and Wagtails. Lynx Edicions, Barcelona.
4.Narosky, T. & S. Salvador. 1998. Nidificación de las Aves Argentinas: Tyrannidae. Asociación Ornitológica del Plata. Buenos Aires.
5.Short, L. & J. Horne. 2001. Toucans, Barbets and Honeyguides. Oxford University Press. Oxford.
6.Sick, H. 1993. Birds in Brazil: A Natural History. Princeton University Press. New Jersey.
7.Smith, P. & R. P. Clay. in press. A Field Guide to the Birds of Paraguay. Helm. London.