Nest Usurpation by a Female Mississippi Kite (Ictinia mississippiensis)

Virtually all species compete for resources, which can lead to aggressive intraand interspecific interactions between individuals (Scott and Fredericson 1951). These interactions may take the form of displays, aggressive chases, and physical contacts (Jamieson and Seymour 1983, Bildstein and Collopy 1985, Boal 2001). Among conspecifics, these interactions may be agonistic, which is an escalation of behaviors from threat displays (often ritualized) to aggression, ultimately resulting in the submission or death of one combatant (McGlone 1986). For example, territorial Harris’s Hawks (Parabuteo unicinctus) engage in posturing, display, and eventual attack if an intruding conspecific does not leave (Dawson and Mannan 1991). In more extreme cases, individuals may kill and cannibalize conspecifics (Allen et al. 2020). The Mississippi Kite (Ictinia mississippiensis) is a highly social, quasi-colonial species (Skipper 2018, Parker 2020). For example, in 2022 I monitored 52 nests among 20 urban parks (one to eight nests/ park) in Lubbock, Texas, USA, and documented a mean density of one nesting pair per 2.7 ha (62.46 SD). Additionally, large nonbreeding groups may communally roost in trees near occupied nests. Despite such close proximities, aggressive interactions between Mississippi Kites appear to be exceedingly rare, with only a few documented events that usually consist of adults chasing subadults away from nests (Shaw 1985, Parker 2020). In summer 2020, I banded a nesting female Mississippi Kite with a US Geological Survey Bird Banding Lab aluminum leg band and a plastic green-colored band with the white letters ME (hereafter G-ME). I did not band the male of the breeding pair. The pair’s 2020 nesting attempt was successful in fledging one young. On 4 June 2021, I confirmed the female G-ME had returned to the 2020 nest area. The 2020 nest had blown out, but the kites had constructed a new nest and I observed multiple copulations between an unbanded male and G-ME. On 23 June 2021 at approximately 1020 H CST, I approached the G-ME nest to assess breeding status. At this date, all the monitored kite nests in my study were in the incubation stage. Upon my arrival I observed G-ME standing on the north side of the nest and facing an unbanded adult female Mississippi Kite perched in the cup of the nest (Fig. 1). The two kites posed with gaped beaks, nape feathers erected, and wings flared out as they faced each other. An unbanded adult male was perched on a branch approximately 1 m above and to the side of the nest. Although I did not know when the interaction was initiated, I watched for more than 10 min as the two female kites commenced to fight on the nest. They began making pecking strikes at each other, progressing to breast to breast contact and batting at each other with their wings and making pecking strikes toward each other’s faces (Supplemental Material 1). When one bird struck out with its beak, the other would retract its head backward to avoid the strike. This back-and-forth sparring continued for several minutes until the