Cognition and reproductive success in cowbirds

Understanding the relationships between cognitive abilities and fitness is integral to an evolutionary study of brain and behavior. However, these relationships are often difficult to measure and detect. Here we draw upon an opportunistic sample of brown-headed cowbird (Molothrus ater) subjects that had two separate research experiences: First, they engaged in a large series of cognitive tests in David Sherry’s Lab in the Advanced Facility for Avian Research (AFAR) at Western University, then subsequently moved to the Field Avian Research Megalab (FARM) at Wilfrid Laurier University where they lived in large breeding flocks in aviaries with other wild-caught cowbirds. Thus, we had extensive measures of cognitive abilities, breeding behavior, and reproductive success for these birds. We report here, for the fist time, the surprisingly strong connections we found among these different measures. Female cowbirds’ spatial cognitive abilities correlated positively with how intensely they were courted by males, and with their overall egg production. Males’ spatial cognition correlated positively with their ability to engage in singing contests (“countersinging”) with other males. In addition, a separate non-spatial cognitive ability correlated positively with the attractiveness of the songs they sung. In sum, these results suggest the cognitive skills assessed in the lab were strongly connected to breeding behavior and reproductive success. Moreover, since certain cognitive abilities related to different aspects of breeding success, it suggests that cognitive modules may have specialized adaptive value, but also that these specialized skills may interact and influence fitness in surprising ways.

Eavesdropping on Referential Yellow Warbler Alarm Calls by Red-Winged Blackbirds Is Mediated by Brood Parasitism Risk

Referential alarm calls that denote specific types of dangers are common across diverse vertebrate lineages. Different alarm calls can indicate a variety of threats, which often require specific actions to evade. Thus, to benefit from the call, listeners of referential alarm calls must be able to decode the signaled threat and respond to it in an appropriate manner. Yellow warblers (Setophaga petechia) produce referential “seet” calls that signal to conspecifics the presence of nearby obligate brood parasitic brown-headed cowbirds (Molothrus ater), which lay their eggs in the nests of other species, including yellow warblers. Our previous playback experiments have found that red-winged blackbirds (Agelaius phoeniceus), a species also parasitized by brown-headed cowbirds, eavesdrop upon and respond strongly to yellow warbler seet calls during the incubation stage of breeding with aggression similar to responses to both cowbird chatters and predator calls. To assess whether red-winged blackbird responses to seet calls vary with their own risk of brood parasitism, we presented the same playbacks during the nestling stage of breeding (when the risk of brood parasitism is lower than during incubation). As predicted, we found that blackbirds mediated their aggression toward both cowbird chatter calls and the warblers’ anti-parasitic referential alarm calls in parallel with the low current risk of brood parasitism during the nestling stage. These results further support that red-winged blackbirds flexibly respond to yellow warbler antiparasitic referential calls as a frontline defense against brood parasitism at their own nests.

Referential alarm calling elicits future vigilance in a host of an avian brood parasite

Yellow warblers ( Setophaga petechia ) use referential ‘seet’ calls to warn mates of brood parasitic brown-headed cowbirds ( Molothrus ater ). In response to seet calls during the day, female warblers swiftly move to sit tightly on their nests, which may prevent parasitism by physically blocking female cowbirds from inspecting and laying in the nest. However, cowbirds lay their eggs just prior to sunrise, not during daytime. We experimentally tested whether female warblers, warned by seet calls on one day, extend their anti-parasitic responses into the future by engaging in vigilance at sunrise on the next day, when parasitism may occur. As predicted, daytime seet call playbacks caused female warblers to leave their nests less often on the following morning, relative to playbacks of both their generic anti-predator calls and silent controls. Thus, referential calls do not only convey the identity or the type of threat at present but also elicit vigilance in the future to provide protection from threats during periods of heightened vulnerability.

Feather mites of the subfamily Pterodectinae (Acariformes: Proctophyllodidae) from passerines and kingfishers in Canada

Investigation of the diversity and taxonomy of feather mites of the subfamily Pterodectinae (Astigmata: Proctophyllodidae) on passerines (Passeriformes) and kingfishers (Coraciiformes: Alcedinidae) in Manitoba revealed 19 species in 5 genera. Of them, eight new species are described, seven of these from passerines and one from a kingfisher: Alaudicola eremophila sp. n. from Eremophila alpestris (Alaudidae), Amerodectes icteri sp. n. from Icterus galbula (Icteridae), A. pheucticus sp. n. from Pheucticus ludovicianus (Cardinalidae), A. tiffanyluiae sp. n. from Oporornis agilis (Parulidae), A. tretiakae sp. n. from Molothrus ater (Icteridae), Tyrannidectes sealyi sp. n. from Tyrannus tyrannus (Linnaeus, 1758) (type host) and Tyrannus verticalis Say, and T. empidonicus sp. n. from Empidonax minimus (Tyrannidae), and Proterothrix megaceryle sp. n. from Megaceryle alcyon (Alcedinidae). Additionally, nine pterodectine species are reported for the first time in the fauna of Canada. Based on re-evaluation of diagnostic charcters, new diagnoses are proposed for the genera Amerodectes, Tyrannidectes, and Metapterodectes, and species contents of these genera are revised. Four species are transferred from the genus Amerodectes to Tyrannidectes with the new combinations proposed: T. caribaeus (Mironov and González-Acuña, 2011) comb. n., T. charitomenos (Hernandes, 2018) comb. n., T. pitangi (Mironov, 2008) comb. n., T. vireonis (Hernandes and Pedroso, 2016) comb. n. Six species are transferred from the genus Tyrannidectes to Metapterodectes with the new combinations: M. amaurochalinus (Hernandes and Valim, 2006) comb. n., M. cinclodes (Mironov and González-Acuña, 2011) comb. n., M. crassus (Trouessart, 1885) comb. n., M. falcklandicus (Mironov and González-Acuña, 2011) comb. n., M. fissuratus (Hernandes and Valim, 2005) comb. n., and M. pteroptochi (Mironov and González-Acuña, 2015) comb. n.

Owens Valley nesting willow flycatcher under pressure

Willow flycatchers (Empidonax traillii; WIFL) nest along the Owens River and Horton Creek in the Owens Valley. Migrating WIFL visit these sites as well as many other tributaries to both the Owens River and Mono Lake. We estimate there are approximately 35 WIFL territories in the Owens valley, or 5% of territories in California. Nesting WIFL in the Owens Valley are likely the federally endangered southwestern subspecies (E. t. extimus; SWIFL). The Chalk Bluff nesting site is particularly important as large nesting areas tend to be both rare and important for SWIFL and it contains more than half (63%) of all known WIFL territories in the region, which also represents 12% of all nesting SWIFL in California. Between 2014 and 2016, WIFL territory numbers declined from 37 to 27 across the three largest breeding sites. Territory numbers may have been influenced by drought conditions or brown-headed cowbird (Molothrus ater; BHCO) nest parasitism. In 2015 and 2016, comprehensive nest monitoring found nest parasitism rates were >40%, and nest success was lower in parasitized nests (16%; N = 5/31) compared with non-parasitized nests (60%; N = 31/52). BHCO management could potentially improve nest success for WIFL as well as many other open-cup nesting riparian birds in the Owens Valley.

Variation in female songbird state determines signal state needed to evoke copulation

It is the female response to male signals that determines courtship success. In most songbirds, females control reproduction via the copulation solicitation display (CSD), an innate, stereotyped posture produced in direct response to male displays. Because CSD can be elicited in the absence of males by the presentation of recorded song, CSD production enables investigations into the effects of underlying signal features and behavioral state on female mating preferences. Using computer vision to quantify CSD trajectory in female brown-headed cowbirds (Molothrus ater), we show that both song quality and a female's internal state predict CSD production, as well as the onset latency and duration of the display. We also show that CSD can be produced in a graded fashion based on both signal strength and internal state. These results emphasize the importance of underlying receiver state in determining behavioral responses and suggest that female responsiveness acts in conjunction with male signal strength to determine the efficacy of male courtship.

Evidence of Brood Parasitism and Quantification of Rangewide Overlap between the Olive Warbler and Brown-headed Cowbird

Brood parasitism is a fascinating natural history phenomenon that provides a window into the coevolution of antagonistic interactions. Many ecological and evolutionary aspects of brood parasitism remain unknown, and new hosts of brood parasites are still being discovered. We document the second instance of brood parasitism of the Olive Warbler (Peucedramus taeniatus) by the Brown-headed Cowbird (Molothrus ater). Apparent lack of habitat and elevation overlap across the ranges of these two species prompted us to examine how frequently they come into contact. We analyzed >3 million Olive Warbler and Brown-headed Cowbird occurrence records from two open-source repositories, eBird and GBIF, to examine both synchronous and asynchronous locality overlap during the breeding season. We found that the two species were documented together simultaneously in only 3.1% of analyzed instances, but that they co-occurred in similar habitat types and/or at similar elevations at 11.8% of localities analyzed across the Olive Warbler’s range. Additional research on aspects of ecology and evolution, such as host selection, the cowbird’s diurnal patterns of movement, and the dynamics of intracellular pathogens infecting brood parasites and their hosts, may shed light more broadly on the ecological interactions and mechanisms underlying brood parasitism.

Developmental asynchrony and host species identity predict variability in nestling growth of an obligate brood parasite: a test of the “growth-tuning” hypothesis

Generalist obligate brood parasites are excellent models for studies of developmental plasticity, as they experience a range of social and environmental variation when raised by one of their many hosts. Parasitic Brown-headed Cowbirds (Molothrus ater (Boddaert, 1783)) exhibit host-specific growth rates, yet cowbird growth rates are not predicted by hosts’ incubation or brooding periods. We tested the novel “growth-tuning” hypothesis which predicts that total asynchrony between cowbirds’ and hosts’ nesting periods results in faster parasitic growth in nests where host young fledge earlier than cowbirds. We tested this prediction using previously-published and newly-added nestling mass data across diverse host species. Total nesting period asynchrony (summed across incubation and brooding stages) predicted cowbird growth; 8-day old cowbirds were heavier in host nests with relatively shorter nesting periods. We further explored the drivers of variation in growth using mass measurements of cowbirds in Song Sparrow (Melospiza melodia (Wilson, 1810)) and Red-winged Blackbird (Agelaius phoeniceus (Linnaeus, 1766)) nests. Our top models included host species (cowbirds grew faster in sparrow nests), numbers of nestmates (slowest when raised alone), and sex (males grew faster). These results confirm that multiple social and environmental factors predict directional patterns of developmental plasticity in avian generalist brood parasites.