Jennifer R. Foote

Black-capped chickadee dawn choruses are interactive communication networks

Summary The dawn chorus of songbirds provides an ideal opportunity to study communication networks because multiple singers are within signalling range of each other, permitting eavesdropping by both males and females. Using an Acoustic Location System, we examined the dawn chorus singing behaviour of male black-capped chickadees (Poecile atricapillus )i n 15 neighbourhoods to determine whether singing behaviour is consistent with the communication network model. We calculated levels of frequency matching for 19 focal males and all of their neighbours. The observed level of frequency matching was greater than expected by chance. All males were involved in multi-way matching at dawn and often matched two or three neighbours simultaneously. The identity of individuals involved in three-way matches was related to both previous winter-flock membership and the relative dominance rank of the interacting males. We show that male black-capped chickadee dawn choruses are interactive communication networks where males are involved in high levels of matching with neighbours, and they match multiple individuals both simultaneously and sequentially. Additionally, the existence of multi-way matching and the identities of individuals involved suggest that individual males may eavesdrop at dawn. This is the first study to quantify network communication during the dawn chorus in multiple neighbourhoods.

Dawn chorus start time variation in a temperate bird community: relationships with seasonality, weather, and ambient light

AbstractThe avian dawn chorus is a daily period of high song output performed predominantly during the breeding season. Dawn chorus performance varies at both the individual and species level. The many extrinsic factors that may relate to dawn chorus start times for different North American bird species have received little attention. In this study, we consider relationships between dawn chorus start times and ambient temperature, precipitation, cloud cover, lunar phase, and Julian date for six common bird species living in a northern temperate rural area. Overall, birds began singing earlier with full or third quarter moon (when moonlight is present at dawn) and with increasing temperature at nautical twilight, and birds began singing later with the presence of cloud cover and precipitation. Our results indicate that a different suite of environmental factors influenced the chorus start times of different species and to different degrees. Alder flycatchers begin singing earliest in this group of birds, followed by Song Sparrows, White-throated Sparrows, American Robins, Eastern Phoebes, and Black-capped Chickadees. This investigation reveals that extrinsic abiotic factors have a significant effect on the dawn chorus start times of north temperate birds, and represents the first comprehensive study of dawn chorus start time variation in North American birds.ZusammenfassungVariation im Beginn des Morgengesangs in einer Brutvogelgemeinschaft gemäßigter Zonen: Beziehungen mit Saisonalität, Wetter und Umgebungslicht Der Morgengesang von Vögeln ist täglich eine Periode hoher Gesangsaktivität vorwiegend während der Brutzeit. Die Darbietung des Morgengesangs variiert sowohl auf dem Individuen- als auch auf dem Artniveau. Den vielen extrinsischen Faktoren, mit denen der Beginn des morgendlichen Gesangs verschiedener nordamerikanischer Vogelarten zusammenhängt, wurde wenig Beachtung geschenkt. In dieser Studie betrachten wir die Zusammenhänge zwischen dem Beginn des Morgengesangs und der Umgebungstemperatur, Niederschlag, Bewölkung, Mondphase und Julianisches Datum für sechs verbreitete Vogelarten in einem nördlichen gemäßigten ländlichen Gebiet. Insgesamt begannen die Vögel früher zu singen bei Voll- oder Dreiviertelmond (Mondlicht noch in der Dämmerung) und mit ansteigender Temperatur während der nautischen Dämmerung. Die Vögel begannen später zu singen bei Bewölkung und Niederschlag. Unsere Ergebnisse deuten darauf hin, dass unterschiedliche Umweltfaktoren den Gesangsbeginn verschiedener Arten in unterschiedlicher Weise beeinflussen. Erlentyrannen beginnen am frühestens mit dem Gesang, gefolgt von Singammer, Weißkehlammer, Wanderdrossel, Weißbauch-Phoebetyrann und Schwarzkopfmeise. Die Untersuchung zeigte, dass extrinsische abiotische Faktoren einen signifikanten Effekt auf den Beginn des Morgengesangs von Vögeln nördlicher gemäßigter Zonen haben. Diese Studie ist zudem die erste Umfassende zu Variationen im Beginn des Morgengesangs nordamerikanischer Vögel.

Tied to the nest: male black-capped chickadees decrease dawn chorus movement behaviour when their mate is fertile

Male songbirds typically mate-guard by closely following the female during her fertile period. At dawn, males may sing near the nest or roost to direct their chorus at mates. Recent evidence suggests males may also be involved in singing interactions with neighbours during the dawn chorus. We used a 16channel acoustic location system to examine the movement behaviour of 37 male black-capped chickadees, Poecile atricapillus, during the dawn chorus to determine if male proximity to the nest is a function of breeding stage. Males with fertile females covered a significantly smaller area within their territory, made fewer long-distance movements and sang at a lower song rate compared to males with nonfertile females. Males with fertile mates remained significantly closer to their nest cavity than males with incubating mates. Males with nonfertile mates spent more time near their neighbours with fertile mates than near their neighbours with nonfertile mates. Neither social rank nor age had a significant effect on movement behaviour or song rate. Our results clearly show that female fertility influences dawn chorusing behaviour in male black-capped chickadees. Males may remain near their nest to minimize the risk of cuckoldry, but when their partner is not fertile males may increase movement behaviour to interact with neighbours and/ or to advertise to potential extrapair mates.

Post-contest behaviour in black-capped chickadees (Poecile atricapillus): loser displays, not victory displays, follow asymmetrical countersinging exchanges

Victory displays are behaviours that occur after the conclusion of a signaling contest, performed solely by the contest winner. Victory displays may reinforce the dominance of the winner either to the loser or to other conspecifics within signaling range. Victory displays are poorly studied despite the significant consequences that post-conflict behaviour may have on the individuals involved. We examined the period immediately following 50 territorial countersinging contests between males in 10 neighbourhoods of black-capped chickadees (Poecile atricapillus) of known dominance rank. We characterized the post-contest singing behaviour of chickadees and evaluated whether post-contest behaviour is consistent with victory displays. Using a 16-microphone acoustic location system to simultaneously record entire neighbourhoods of breeding chickadees, we isolated 50 dyadic countersinging contests and measured the vocal behaviour of the contestants in the minutes following each interaction. Eighty-six percent of contests were followed by a period of solo singing by one of the contestants, while 14% were followed by silence. The post-contest singer was most often the contestant who held a subordinate dominance position in the previous winter’s dominance hierarchy; dominant males performed post-contest song bouts significantly less often. Asymmetry in overlapping between contestants did not predict which bird sang a post-contest bout. However, in a significant majority of cases, the post-contest singer was pitch-matched by his opponent during the contest more than he pitch-matched his opponent. Our results indicate that male chickadees do not perform acoustic victory displays after countersinging contests. In contrast, the post-contest behaviour of territorial chickadees is more consistent with a “loser display”.

Songs of the Eastern Phoebe, a suboscine songbird, are individually distinctive but do not vary geographically

Animal displays may vary both within and among individuals and also within and among populations. This variation may contain important information used by animals for individual recognition. Suboscine birds are thought to develop song by fully innate mechanisms and are poorly studied relative to oscine birds, where song learning results in significant variation in song structure among individuals and the development of dialects. Recent research, however, demonstrates that suboscine song is often individually distinctive and in some cases shows signs of regional variation. We used spectrogram cross-correlation and canonical discriminant function analysis to examine individual and geographic variations in songs of Eastern Phoebes (Sayornis phoebe), suboscine birds with two song types. Both song types were individually distinctive and showed significantly higher cross-correlations within than among individuals. Discriminant function analysis correctly assigned 85.3% of “phee-bee” and 90.0% of “phee-b-be-bee” songs to the correct male, levels that are significantly higher than expected by chance. The individually distinctive characters of songs were also significantly repeatable among recording sessions. Eastern Phoebe song did not vary geographically between two populations separated by 640 km; permuted discriminant function analysis assigned 65% of “phee-bee” and 70% of “phee-b-be-bee” songs to the correct population, which did not differ significantly from chance expectations. Variation among males in song characteristics could be used by both males and females to discriminate among individuals. These detailed bioacoustic analyses support the idea that individual distinctive acoustic signals are widespread across suboscine birds.

Comparison of autonomous and manual recording methods for discrimination of individually distinctive Ovenbird songs

Many animals produce individually distinctive vocalizations with increased outputs during the breeding season. Many animals, including birds, can recognize other individuals based on the distinctive features of their songs and researchers can use bioacoustics tools to discriminate among individuals. Typically, bioacoustics analyses use recordings made with highly directional microphones that are free of background noise and spectral overlap. However, recent technological advances in automated recording have made it possible to record remotely and cover larger areas simultaneously. We tested whether spectrogram cross-correlation can be used to discriminate among songs of 19 individual Ovenbirds (Seiurus aurocapillus). We used two microphone types: directional (Sennheiser MKH-70) and omnidirectional (SMX-II) microphones. Because birds may vary in their distance from the SMX-II microphones, songs were selected as either high-quality (close to the recorder) or low-quality (further away from the recorder). We found that all recording types could be used to discriminate the songs of individual male Ovenbirds from other males in the population. Discrimination among directional recordings was significantly better than among omnidirectional recordings, and high-quality recordings could be used to discriminate among individuals significantly better than low-quality recordings. Taken together, our results suggest that automated omnidirectional recording could be valuable for future behavioural research allowing individuals to be followed over an entire breeding season. In addition, acoustic surveys of communities could provide information about abundance as well as presence and/or absence of species.

DAWN SINGING OF EASTERN PHOEBES VARIES WITH BREEDING STAGE AND BROOD NUMBER

ABSTRACT The dawn chorus is a daily period of continuous singing by male songbirds that begins prior to sunrise. It is relatively less studied than daytime singing, and particularly in suboscine birds. We analyzed dawn singing of 14 Eastern Phoebes (Sayornis phoebe) in Echo Bay, Ontario over the 2011–2012 breeding seasons. We measured time of first song, length of dawn bout, time of final song, average song rate, and peak song rate and compared these characteristics among breeding stages. Results indicated that breeding stage was a significant predictor of all five dawn song features. Our results suggest that dawn singing of Eastern Phoebes is directly related to female fertility. We show that males begin singing significantly earlier when females are fertile. Males sang significantly longer during fertile and incubation stages than while feeding young. Males began singing later and sang for the shortest duration during the pre-breeding period. Song rates were higher in first broods than in second broods. We showed that suboscine dawn signaling patterns vary across breeding seasons in ways similar to oscine songbirds.

Decoding the ‘zeep’ complex: quantitative analysis of interspecific variation in the nocturnal flight calls of nine wood warbler species (Parulidae spp.)

ABSTRACT The “zeep” complex consists of nine birds that produce nocturnal flight calls with similar acoustic features. Our inability to distinguish these calls inhibits the acoustic monitoring of these species. We test the hypothesis that flight calls of nine warblers in the “zeep” complex show sufficient acoustic differences to allow differentiation. We investigate divergence in these vocalizations by recording birds held for banding and collecting additional recordings from sound libraries. We used three approaches to compare calls between species: analysis of variance in acoustic properties, discriminant analysis of acoustic properties, and spectrographic cross-correlation. The first approach revealed five species that were different in one or more acoustic properties. The second approach revealed a level of assignment to the correct species (73%) that exceeded levels expected by chance (36%). The third approach revealed calls of seven species to be significantly more similar to conspecific calls than heterospecific calls. Our results suggest the calls of many members of the “zeep” complex exhibit species-specific differences in structure, which may allow differentiation of at least five “zeep” species based on call alone. We advocate for the combined use of these three approaches for the comparison of “zeep” calls in future flight call studies.

Herring Gulls (Larus argentatus) Depredate Chimney Swifts (Chaetura pelagica) at a Migratory Roost

ABSTRACT We describe a new predator-prey relationship between Herring Gulls (Larus argentatus) and Chimney Swifts (Chaetura pelagica) at a communal roost in Sault Ste. Marie, ON, Canada. In a season-long study in 2015, we document 38 instances of predation, an estimate which likely underestimates the extent of total predation pressure. Chimney Swifts were captured on-the-wing by Herring Gulls.