Ken A. Otter

Do female great tits (Parus major) assess males by eavesdropping? A field study using interactive song playback

Male singing behaviour correlates with extra–pair success in several passerine birds. Singing interactions during territorial contests provide relative information on the males involved. Such information may be important in female extra–pair behaviour and eavesdropping on singing interactions among males may allow females to make such relative assessments. We used interactive playback to instigate singing contests with male great tits during the peak fertile period of their mate in an attempt to alter females ‘assessment of mates’ quality relative to neighbours (potential extra–pair partners). We escalated a contest to one male (by overlapping his songs) and then subsequently de–escalated a contest (by alternating) to a neighbour. Intrusions onto neighbouring territories by females mated to either treatment male were then monitored. Females mated to escalation treatment males were more likely to intrude following playbacks than females mated to de–escalation treatment males. Although the absolute song output of males did not differ between treatments, males produced more song relative to playback in de–escalation treatments and relative song output was positively correlated with female intrusions. Therefore, female great tits eavesdrop on singing interactions and change their visitation rates to neighbouring territories according to their mates singing performance relative to neighbours.

The design of artificial nestboxes for the study of secondary hole-nesting birds: a review of methodological inconsistencies and potential biases

Abstract. The widespread use of artificial nestboxes has led to significant advances in our knowledge of the ecology, behaviour and physiology of cavity nesting birds, especially small passerines. Nestboxes have made it easier to perform routine monitoring and experimental manipulation of eggs or nestlings, and also repeatedly to capture, identify and manipulate the parents. However, when comparing results across study sites the use of nestboxes may also introduce a potentially significant confounding variable in the form of differences in nestbox design amongst studies, such as their physical dimensions, placement height, and the way in which they are constructed and maintained. However, the use of nestboxes may also introduce an unconsidered and potentially significant confounding variable due to differences in nestbox design amongst studies, such as their physical dimensions, placement height, and the way in which they are constructed and maintained. Here we review to what extent the characteristics of artificial nestboxes (e.g. size, shape, construction material, colour) are documented in the ‘methods’ sections of publications involving hole-nesting passerine birds using natural or excavated cavities or artificial nestboxes for reproduction and roosting. Despite explicit previous recommendations that authors describe in detail the characteristics of the nestboxes used, we found that the description of nestbox characteristics in most recent publications remains poor and insufficient. We therefore list the types of descriptive data that should be included in the methods sections of relevant manuscripts and justify this by discussing how variation in nestbox characteristics can affect or confound conclusions from nestbox studies. We also propose several recommendations to improve the reliability and usefulness of research based on long-term studies of any secondary hole-nesting species using artificial nestboxes for breeding or roosting.

Do female black-capped chickadees prefer high-ranking males as extra-pair partners ?

Abstract Previous studies have shown that some female black-capped chickadees (Poecile atricapillus) solicit copulations from males that rank higher in winter flocks than their social mates, and extra-pair paternity in nests occurs commonly enough to be considered a potential female mating tactic. This study uses blood samples collected in 1992–1995 from 58 families of black-capped chickadees to test whether females with extra-pair offspring have chosen extra-pair sires higher in social rank than their mates. Paternity was assessed with multilocus DNA fingerprinting in 1992–1994 nests and with microsatellite and single-locus minisatellite DNA typing in 1995 nests. Seventeen of 58 nests (29.3%) contained young genetically mismatched with their social father. In 11 of 15 cases where the identity of the extra-pair male was known, the extra-pair male was dominant to the social father. Using data from 29 nests located in 1994 and 1995 for which we had the most data on relative ranks of males, high-ranking males had greater realized reproductive success than low-ranking males as a result of extra-pair fertilizations. There was no significant difference between the number of nests containing extra-pair young of females mated to low-ranked versus high-ranked males. Two nests in 1995 contained young either genetically mismatched with both social parents (intraspecific brood parasitism) or, in one nest, genetically mismatched with the social mother but not the social father (quasi-parasitism). The implications of female strategies acquiring genetic benefits through extra-pair copulations are discussed.

Female initiated divorce in a monogamous songbird: abandoning mates for males of higher quality

Divorcing a current partner to re-pair with a mate of higher quality may be a strategy to increase reproductive success used by socially monogamous birds. By increasing the availability of males through selective mate removal during the nest building period, we found that female black-capped chickadees, Parus atricapillus, will desert their mates to pair with males of higher social rank, a trait closely associated with resource holding potential in this species. Females from neighbouring territories were more likely to desert their mates for high ranked rather than the low ranked widower males; six of seven high ranking and one of six low ranking males were chosen by the divorcing females. Six of the seven widower males chosen by divorcing females were dominant to the males that the females deserted. Once released, the originally removed females were able to re-establish pairbonds with their mates. Higher social ranks of removed females may have enabled them to exclude lower ranked replacement females, and may reflect a natural constraint on female choice.

Extra-Pair Paternity in the Black-Capped Chickadee

Studies of the mating strategies of birds are increasingly shifting their focus to the role that females take in controlling copulation (Hunter et al. 1993, Petrie 1992, Birkhead and Moller 1993). In some avian species, females appear able to control whether copulations occur by accepting or rejecting copulation attempts (BjSrklund et al. 1992, Lifjeld and Robertson 1992, Westneat 1992). Similarly, females of some species actively solicit copulations by seeking the extra-pair male in his own territory (Smith 1988, Kempenaers et al. 1992, Venier et al. 1993). In species where females do control the outcome of copulation attempts, there is a need to, first, determine the extent that extra-pair copulations (EPCs) lead to fertilizations and, second, establish potential benefits that a female may obtain by engaging in EPCs. Smith (1988) reported that female Black-capped Chickadees, Parus atricapillus, seek EPCs from males on territories adjacent to the territory defended by the females mate. Interestingly, Smith observed that females preferentially sought males for EPCs that held higher dominance rank than the females mate in the preceding winters flock. Thus, female Black-capped Chickadees may be engaging in a mixed reproductive strategy of social monogamy while increasing reproductive success by extra-pair copulations with males of higher genetic quality than their own mate (Trivers 1972, Smith 1988, Hamilton 1990). Females may also benefit from engaging in EPCs with dominant males if, by doing so, this facilitates rapid pair bonding with the dominant male in the event that his mate dies. There is a need for data on whether EPCs are resulting in extra-pair paternity of the nestlings in order to imply a fitness benefit to the females behavior. In this study we document rates of extra-pair paternity in an Ontario population of Black-capped Chickadees, using DNA fingerprinting, and provide support for Smiths hypothesis by showing that extra-pair males were of higher dominance rank than the females mate. We also suggest a paternity-related explanation for occasional observations ofpolyandry in chickadees (Waterman et al. 1989, Howitz 1991).

Changes in singing behavior of male black-capped chickadees (Parus atricapillus) following mate removal

We removed the mates of ten male black-capped chickadees (Pares atricapillus) during the nest-building period to determine the effect of female presence on dawn singing. During the first dawn chorus following mate removal, males sang significantly longer, increased movement within their territory, and increased the percentage of their territory covered while singing. After the female was returned, these parameters returned to the pre-removal values. Males did not alter the frequency range or modal frequency of their songs when the mate was removed, nor did they change the degree of frequency shifting in the fee-bee song. We conclude that dawn singing in the black-capped chickadee acts, in part, as an intersexual signal, and that the behavior of frequency shifting in the song may be directed more toward rival males than females.

Nest-site selection by female black-capped chickadees : Settlement based on conspecific attraction?

Female Black-capped Chickadees (Poecile atricapillus) solicit extrapair copu- lations (EPCs) from neighboring high-ranked males, and these EPCs result in extrapair young. Females might choose to locate their nests near the territory boundaries of attractive males to facilitate access to EPCs. Other hypotheses might also explain choice of nest site, namely: (1) habitat characteristics, (2) prey abundance, and (3) previous experience. We test- ed these four hypotheses in 1996 and 1997. Out of 27 habitat characteristics measured, we found only one that was significantly different between nests and control sites in both years. The abundance of large trees was lower at nest sites than at control sites in each year and when years were pooled. Relative prey abundance did not differ between nests and control sites for either year of the study. We found no difference in interyear nest placement based on female experience; experienced females nested farther than 60 m from their previous nest sites in both years of the study. In 1996, females whose neighboring males were higher ranked than their social partner located their nests significantly closer to territory bound- aries than did females whose nearest neighbors were lower ranked than their social partner. In 1997, all pairs nested near territory boundaries. We conclude that choice of nest location in Black-capped Chickadees is influenced by conspecific attraction based on mating tactics.

Dominance signalled in an acoustic ornament

In many species, males use auditory signals to attract females and females select males based on their dominance status. Here we show that information on dominance status in male black-capped chickadees, Poecile atricapillus, a small, temperate, North American songbird, can be extracted from individual songs. We found that the relative amplitude of the two notes in the ‘fee bee’ song of this species was more consistent in dominant males. Furthermore, females responded differently to presentations of single song exemplars from males of different dominance status, with females vocalizing more and performing more motor behaviours during the presentation of dominant songs. Our study suggests that non-pitch-based cues within single vocalizations can both reliably indicate relative rank and be discriminated by females. 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. The concept of dominance was first developed by SchjelderupEbbe (1935) when studying fowl (Gallus gallus), who coined the term ‘pecking order’. Today, dominance has taken on broader meanings. Dominance is a relative measure based on encounters between individuals in which one individual asserts itself over another. Such hierarchies among individuals that repeatedly interact with one another serve to reduce future aggressive interactions. How individual animals display their dominance status to conspecifics is a matter of great importance for intra- and intersexual communication. In particular, being a dominant male

EFFECTS OF HABITAT DISTURBANCE ON REPRODUCTION IN BLACK-CAPPED CHICKADEES (POECILE ATRICAPILLUS) IN NORTHERN BRITISH COLUMBIA

Abstract Avian species that persist in breeding in disturbed habitats are often thought to be less affected by disturbance than habitat specialists lost following disturbances, yet there is growing evidence that human-altered environments may negatively affect reproductive behavior and nest success of those generalists as well. We compared nest success of Blackcapped Chickadees (Poecile atricapillus) in two adjacent habitats: a mature mixed-wood forest (undisturbed) and a forest regenerating after logging (disturbed). Despite similar breeding densities, proportion of nests that successfully fledged young was lower in the disturbed habitat than in the undisturbed habitat. Abandonment was the most common cause of nest failure. A within-habitat comparison of the social rank of birds revealed that low-ranking birds had lower nest success than high-ranking birds in the disturbed, but not in the undisturbed, habitat. Clutch size and brood size of nests that progressed to the point of hatch did not differ significantly between habitats. Average total number of fledglings produced per pair, though not significantly different, was suggestively lower in the disturbed habitat. Across habitats, nests situated in snags with lower amounts of internal decay were more successful. Successful nests were also located in sites with higher canopy height, low understory density below 1 m, and higher understory density between 2 and 3 m—all attributes generally associated with undisturbed, mature forests in the region. Our results provide evidence that disturbed habitats may represent poor-quality habitat for this forest generalist, and that habitat quality differentially affects individuals, depending on their dominance rank.

Learning to cope: vocal adjustment to urban noise is correlated with prior experience in black-capped chickadees

Urban noise can interfere with avian communication through masking, but birds can reduce this interference by altering their vocalizations. Although several experimental studies indicate that birds can rapidly change their vocalizations in response to sudden increases in ambient noise, none have investigated whether this is a learned response that depends on previous exposure. Black-capped chickadees (Poecile atricapillus) change the frequency of their songs in response to both fluctuating traffic noise and experimental noise. We investigated whether these responses to fluctuating noise depend on familiarity with noise. We confirmed that males in noisy areas sang higher-frequency songs than those in quiet areas, but found that only males in already-noisy territories shifted songs upwards in immediate response to experimental noise. Unexpectedly, males in more quiet territories shifted songs downwards in response to experimental noise. These results suggest that chickadees may require prior experience with fluctuating noise to adjust vocalizations in such a way as to minimize masking. Thus, learning to cope may be an important part of adjusting to acoustic life in the city.