Ken Yasukawa

Beloit College · Department of Biology

I used 20 years of nest records and predation at silent control and begging-call playback nests to determine whether begging calls of Red-winged Blackbirds (Agelaius phoeniceus) attract predators. Survival analysis provided no evidence that vocal begging affected nest predation. Survival schedules during egg and nestling periods were not significan...

The Red-winged Blackbird (Agelaius phoeniceus; redwing) is a commonly used accepter host species that incubates eggs and cares for nestlings and fledglings of the obligate brood parasitic Brown-headed Cowbird (Molothrus ater; cowbird). This host species, however, may reduce the risk of parasitism with a frontloaded antiparasite strategy in which it...

Although some signals seem adapted to maximize transmission of cues to intended receivers, others appear to have been selected to deny specific types of cues to unwanted receivers. We review three categories of avian vocal signals that have been suggested to show adaptation for cue denial: aerial predator alarm calls, begging calls, and soft songs...

We tested the nestling discrimination hypothesis by observing responses of female Red-winged Blackbirds (Agelaius phoeniceus) to playback of begging calls by conspecifics or Brown-headed Cowbirds (Molothrus ater). Female redwings departed the nest to forage and returned with food significantly faster in response to redwing playback than to cowbird...

The brown-headed cowbird (Molothrus ater) is an obligate brood parasite known to use over 200 host species. The red-winged blackbird (Agelaius phoeniceus) is a commonly used accepter host that incubates cowbird eggs and cares for cowbird nestlings and fledglings. This host species, however, may reduce the risk of parasitism with a frontloaded antip...

The brown-headed cowbird (Molothrus ater) is an obligate brood parasite known to use over 200 host species. The red-winged blackbird (Agelaius phoeniceus) is a commonly used accepter host that incubates cowbird eggs and cares for cowbird nestlings and fledglings. This host species, however, may reduce the risk of parasitism with a frontloaded antip...

Many songbirds are socially monogamous but genetically polyandrous, mating with individuals outside their pair bonds. Extra-pair paternity (EPP) varies within and across species, but reasons for this variation remain unclear. One possible source of variation is population genetic diversity, which has been shown in interspecific meta-analyses to cor...

Background: CXCL1 is a chemotactic cytokine shown to regulate breast cancer progression and chemo-resistance. However, the prognostic significance of CXCL1 expression in breast cancer has not been fully characterized. Fibroblasts are important cellular components of the breast tumor microenvironment, and recent studies indicate that this cell type...

The ability of sexually mature non-territorial floaters to sire offspring affects the success of floating as a breeding strategy. Red-winged Blackbirds (Agelaius phoeniceus) have second-year (SY) and after-second-year (ASY) floater males, and genetic studies suggest that floaters may gain paternity. Despite these studies, we still know little about...

Nestlings communicate with parents via begging, but what does begging signal and how do parents allocate food to their nestlings? We tested the signal-of-need (SoN) and signal-of-quality (SoQ) hypotheses for nestling begging in the Red-winged Blackbird (Agelaius phoeniceus) by attempting to determine whether begging is negatively (SoN) or positivel...

Nestling begging and parental provisioning can attract nest predators and reduce reproductive success, so parents and their offspring might be expected to respond adaptively by minimizing predator-attracting cues when predators threaten nests. Male Red-winged Blackbirds (Agelaius phoeniceus) are well known for their antipredator alarm calls that co...

I observed a Red-winged Blackbird (Agelaius phoeniceus) nest in southcentral Wisconsin, USA that received a Yellow-billed Cuckoo (Coccyzus americanus) egg. The cuckoo egg was laid after the blackbird clutch was complete and the female had begun incubation. The parasitic egg was considerably different in size and color, but was accepted by the femal...

The epaulets of male Red-winged Blackbirds (Agelaius phoeniceus) are frequently cited as a sexually selected plumage ornament, but a number of laboratory and field studies provide little evidence that they are currently experiencing sexual selection. We used hair dye to dull epaulets of free-living territorial males prior to pair formation to deter...

La mancha alar en los machos de Agelaius phoeniceus funciona tanto en el contexto intra-sexual como inter-sexual, pero existe poca evidencia de que ésta covaríe con el éxito reproductivo en esta especie, que ha sido bastante estudiada. Utilizamos un análisis de pasos usando caracteres territoriales de los machos, éxito de apareamiento y éxito repro...

Estudiamos 19 grupos de la especie con cría cooperativa Malurus cyaneus marcados con anillos de colores para determinar (1) las contribuciones de los machos reproductores y ayudantes a la vigilancia contra depredadores, (2) si dicha vigilancia reduce el riesgo de depredación y (3) los mecanismos a través de los cuales podría reducirlo. El tiempo in...

We conducted experiments on the intersexual and intrasexual consequences of epaulet colour in male red-winged blackbirds, Agelaius phoeniceus. In the female choice experiment, we gave captive females a choice between males with normal or dulled epaulets, and between males with normal or reddened epaulets. Females tended to associate more with norma...

ABSTRACT Although individually distinct begging calls may permit parents to recognize their offspring, birds nesting in dense breeding colonies where fledglings intermingle might benefit from additional adaptations. For example, if the calls of all nestlings in a brood were similar, parents would need to recognize only one brood call instead of the...

Avian brood parasitism reduces the success of parasitized broods, yet most hosts of brown-headed cowbirds, Molothrus ater, neither desert parasitized clutches nor eject parasite eggs. We investigated whether spatial and temporal patterns of repeated cowbird parasitism on individuals influence the benefits of desertion or ejection in prothonotary wa...

Over the past three decades, the red-winged blackbird Agelaius phoeniceus has served as a model species for studies of sexual selection and the evolution of ornamental traits. Particular attention has been paid to the role of the colorful red-and-yellow epaulets that are striking in males but reduced in females and juveniles. It has been assumed th...

Male Red-winged Blackbirds (Agelaius phoeniceus) are known to give alarm calls in response to the approach of a predator, and to encode information about the level of threat in their calling behavior. To determine whether such sentinel males alert females, we conducted a simple field experiment in which we measured the distances at which incubating...

We examined temporal and spatial nesting aggregations in a prairie-nesting population of Red-winged Blackbirds (Agelaius phoeniceus). In particular, we were interested in the effects of aggregated nesting on blackbird nest success and brood parasitism by Brown-headed Cowbirds (Molothrus ater). Most cowbird parasitism occurred early in the breeding...

To examine whether parent-nestling recognition occurs in Red-winged Blackbirds (Agelaius phoeniceus) we exchanged 11 pairs of nestlings matched for sex, mass, and age (6- 9 d old) between pairs of experimental nests. To control for possible effects of nestling reinoval and handling, we also removed and then returned one nestling froin each of nine...

We examined variation in the onset of nocturnal incubation by female Red-winged Blackbirds (Agelaius phoeniceus). Many females began nocturnal incubation after laying the prepenultimate egg, which resulted in asynchronous hatching. This pattern of incubation is consistent with a model that predicts hatching asynchrony when the ratio of nest predati...

We examined brood parasitism by Brown-headed Cowbirds (Molothrus ater) on a prairie-nesting population of Red-winged Blackbirds (Agelaius phoeniceus) from 1984 to 1997 and the extent to which parasitism affected host reproductive success. During this 14-year period, 2-32% of redwing nests were parasitized per year. Two measures of cowbird parasitis...

We map behavioral characters related to mating system onto a phylogeny of the New World blackbirds (family Icteridae) in order to test hypotheses on the evolution of polygyny in Red-winged Blackbirds (Agelaius phoeniceus). The two hypotheses we test are 'long-term models' in the sense that, unlike most polygyny hypotheses, they allow the ancestral...

Nestling birds may honestly signal their need for food to provisioning adults, or begging might be a manipulative attempt to coerce additional food from providers, but in either case, providers respond to an increase in begging with an increase in feeding. We used playback of begging calls recorded from nestlings to determine whether male and femal...

We use two approaches to compare the reproductive success of secondary (S) females to the reproductive success of monogamous and primary (M/P) females in two populations of the polygynous Red-winged Blackbird Agelaius phoeniceus. One approach is to calculate x, the mean reproductive success of all S females divided by the mean reproductive success...

Epaulets of female Red-winged Blackbirds (Agelaius phoeniceus) vary in brightness from brown to bright red-orange. We test predictions of the hypothesis that condition at the time of molt determines female epaulet brightness and that females in superior condition produce brighter epaulets. We compared each female's epaulet with a series of color ph...

The purpose of this book is to explain why red-winged blackbirds are polygynous and to describe the effects of this mating system on other aspects of the biology of the species. Polygyny is a mating system in which individual males form long-term mating relationships with more than one female at a time. The authors show that females choose to mate...

Male red-winged blackbirds (Agelaius phoeniceus) provisioned 50% (118/235) of available broods over an 8-year period. In most cases, each male provisioned only the oldest brood on his territory, but in 21 cases, the male fed a younger brood after first feeding an older one. In 10 of these cases the switch to the younger brood followed predation of...

During the nesting season, male red-winged blackbirds frequently scan from prominent perches near active nests. Males engaged in such behaviour appear to be acting as sentinels, guarding their nests against predators. The sentinel hypothesis was tested in three ways. (1) Male response to a simulated predator was observed. On average, males spent si...

Live and stuffed male and female red-winged blackbirds (Agelaius phoeniceus) were presented to territorial males in order to study the repertoire organization of males during intersexual and intrasexual encounters. Territorial male red-winged blackbirds switched song types more frequently and sang more song types in response to presentation of a fe...

Stepwise multiple linear regression was used to identify the factors that affect the rate at which nestlings were fed by male and female red-winged blackbirds, and the effects of this provisioning on reproductive success. In addition, discriminant function analysis was used to examine the differences between pair-fed and female-fed broods. Both mat...

A speaker-occupation experiment was conducted to determine whether female red-winged blackbirds (Agelaius phoeniceus) use the aggressive Teer vocalization to deter conspecific females that are prospecting for opportunities to settle. In each of 14 trials conducted during the breeding seasons of 1987, 1988, and 1989, tape recordings and a pair of lo...

Understanding the function of behaviour requires analysis of fitness costs and benefits, but this is difficult because methods of assessment are usually lacking. In this paper the results of an experimental analysis of costs and benefits of a vocal signal, the nest-associated calls during arrival and departure from their nests, and while on their n...

Proposes a set of models for the explanation of territorial polygyny, outlines general methods for testing the models, and applies the tests in detail to 4 species. In all species, polygyny seems to be based on female choice rather than on male coercion. For red-winged blackbirds Agelaius phoeniceus, evidence indicates that mating with already-mate...

We studied Red-winged Blackbird (Agelaius phoeniceus) behavior in marsh and prairie habitats to determine whether courting males provide cues of their nest defense, whether females prefer males that defend nests vigorously, and whether male nest defense affects nest success. We found no evidence that courtship behavior provides cues of male nest de...

Tests the hypothesis that sexual selection for characteristics that are advantageous in territory defense or mate acquisition, or both, occurs at the expense of survivorship. Mean annual mortality of territorial male red-wings was 52%. with 29% mortality occurring during the "nonbreeding' season (1 June-1 March) and 22% mortality occurring during t...

We used three models to simulate female choice in red-winged blackbirds. Fidelity of females to the territories on which they nested in the preceding year was insufficient to account for the observed levels of consistency in settlement patterns when first-breeding females and females not faithful to their sites chose randomly among the available te...

Female Song Sparrows (Melospiza melodia) perform more courtship display in response to large repertoires of song types than in response to small repertoires. This preferential response to large repertoires might be due to a positive correlation between repertoire size and male quality; therefore, females might benefit by responding more strongly to...

The Beau Geste hypothesis proposes that song repertoires are advantageous in territory defense because nonterritorial males, who are prospecting for territories, use the number of song types they hear to assess the density of territorial males, and then avoid densely-settled areas. A territorial male can then inflate the apparent density of singers...

We studied the effects of prior residence on contests for status within dominance hierarchies of captive male dark-eyed juncos (Junco hyemalis) to test predictions of a game-theory model of contest behaviour (Maynard Smith & Parker 1976; Hammerstein 1981). Several predictions of the model were supported. (1) Encounters between birds that were equal...

In the case of Agelaius phoeniceus, sexual selection acts strongly on males and affects just those traits in which males differ most from females, viz. size, aggressiveness, plumage, and song. The action of sexual selection on male redwings is mediated through female choice and competition among males. There is also some evidence of sexual selectio...

Female Red-winged Blackbirds (Agelaius phoeniceus) are often aggressive towards conspecific females during the breeding season. We hypothesize that the function of female-female aggression in this species is to guard the nonshareable portion of the male's parental investment. The investment-guarding hypothesis predicts that a female should be more...

Two experiments were conducted to deterine whether territorial male Red-winged Blackbirds discriminate among neighbor, stranger, and self songs. In the first experiment, recordings of the three classes of songs were played to territorial males. Responses to playback of stranger song, as measured by song rate, intensity of Song Spread display, and c...

Male Red-winged Blackbird pairing success was studied to determine the role of male quality in female choice of territory and mate. Data on date of first nest, harem size, and proportion of territorial males surviving to subsequent breeding seasons did not support the hypothesis that territory quality alone determines female choice of mate. Male re...

In a between-species comparison of icterids, male survival decreases relative to female survival as the degree of sexual size dimorphism increases. This result is consistent with the hypothesis that male size is limited by survival selection in icterids; the degree of size dimorphism is known to correlate with the degree of polygyny in icterids, ho...

Song repertoires in the red-winged blackbird (Agelaius phoeniceus) were studied to test the hypothesis that song repertoires have evolved to mimic high density. Results were consistent with predictions of this hypothesis. (1) Song types within a repertoire were as variable as those sung by different males. (2) Males often switched song type when th...

The female choice and male-male competition hypotheses for the evolution of song repertoires were tested by studying repertoire size, pairing success, reproductive experience, and territory size in the Red-winged Blackbird. Analysis of these variables produced the following results:1) Male Red-winged Blackbirds with large song repertoires were more...

The aggressive tendencies of territorial male redwinged blackbirds were tested using playback of conspecific songs and presentation of a male redwing mount. Factor analysis of overt aggressive responses generated three orthogonal indices of aggressive tendencies. These indices were named (1) Distant Approach (rate of flights over, and proportion of...

Thesis (Ph. D.)--Indiana University, 1977. Includes bibliographies. Microfilm. s