J. Bruce Falls

Design of Playback Experiments: The Thornbridge Hall NATO ARW Consensus

Playback is an experimental technique commonly used to investigate the significance of signals in animal communication systems. It involves replaying recordings of naturally occurring or synthesised signals to animals and noting their response. Playback has made a major contribution to our understanding of animal communication, but like any other technique, it has its limitations and constraints.

LONG‐TERM DYNAMICS OF SMALL‐MAMMAL POPULATIONS IN ONTARIO

We analyzed 43 yr of live-trapping data for eight species of small mammals in Algonquin Provincial Park, Ontario. Our primary objective was to test whether complex nonlinear models are necessary to describe dynamics of the Algonquin rodent populations. Variation in abundance among species was related to mean abundance by a simple power function with an exponent of 1.77, implying that population variability did not increase with mean density as much as one might expect for strictly statistical reasons. Time-series analyses of annual population densities indicated no significant autocorrelation functions for five species. Southern red-backed voles, red squirrels, and flying squirrels had significant autocorrelations, but only flying squirrels had an autocorrelation function suggestive of cyclic population dynamics. Per capita rates of population growth were density-dependent in all eight species, although in most cases there was substantial deviation around the fitted regression lines. Response surface models with one- and two-year lags significantly improved the statistical fit to data for three species, but only one of these response surface models was sustainable in the face of realistic stochastic variation in per capita growth. These results suggest that simple logistic models are adequate for predicting the long-term dynamics of the Algonquin small-mammal assemblage. All eight species showed evidence of synchronized population fluctuations over time, suggesting trophic linkages due to shared food resources, shared predators, or both.

A comparison of sound propagation and song frequency in temperate marsh and grassland habitats

SummaryAttenuation of pure tones was measured in marsh and grassland habitat. At surface level, in grassland, the ground effect strongly attenuated frequencies below 2.0 kHz (Fig. 2). The ground effect was reduced by increasing source-receiver elevation. In marsh habitat the ground effect did not occur, and low frequencies were optimal for sound propagation (Fig. 3). As predicted from sound propagation tests, analysis of recorded songs of seven grassland and six marsh species indicated that minimum and emphasized frequency were significantly lower in songs of marsh birds. Maximum frequency did not differ between habitats (Table 4). Buzzing songs of yellow-headed blackbirds were broadcast and re-recorded at 1 and 50 m from the speaker in marsh and grassland habitats. Low frequency components attenuated more rapidly than higher frequency components in grassland, and the reverse occurred in marsh. Results suggested that the ground effect restricts the use of low frequencies by grassland birds. This evidence is consistent with the ‘sound window’ hypothesis of Morton.

DENSITY DEPENDENCE, PREY DEPENDENCE, AND POPULATION DYNAMICS OF MARTENS IN ONTARIO

Ecological factors influencing demographic parameters of mammalian carnivores are poorly understood, due to the difficulty of simultaneously measuring predator and prey populations over an extended period. We used cohort analysis based on age-specific harvest data to estimate population densities over 20 yr for martens (Martes americana). Marten abundance increased threefold over the study period, probably due to relaxation in harvest intensity at the beginning of the study interval. Changes in rates of population growth by martens were positively correlated with population densities of three species of small mammals recorded over the same time span: deer mice (Peromyscus maniculatus), red squirrels (Tamiasciuris hudsonicus), and flying squirrels (Glaucomys sabrinus). We found no evidence of short-term cycles in marten abundance, nor were there significant cross-correlations at lags greater than 1 with prey population densities. Martens also showed evidence of density-dependent population growth. Such density dependence beyond the demographic effect of variation in prey density was possibly due to agonistic interactions among territory holders. Such mixtures of prey dependence and density dependence often have a stabilizing influence in theoretical models, which could contribute to the observed stability of deer mouse, red squirrel, and marten populations in Algonquin Park. Harvest intensity was negatively related to yearly variation in marten population growth. Mortality due to trapping averaged 37.9% over two decades, with no detectable relationship to changes in marten population density. Hence, harvesting acted as a stochastic external variable that was additive to density-dependent and prey-dependent effects.

Vocal recognition between parents and young of ancient murrelets, Synthliboramphus antiquus (Aves: Alcidae)

Vocalization is a conspicuous feature of the departure of family groups of ancient murrelets, Synthliboramphus antiquus, from their colonies. The nocturnal timing of departure and the temporary separation of adults and chicks, followed by their reunion among many conspecifics, suggest that they recognize one another by their vocalizations. In this study, the calls of adults showed greater between- than within-individual variability, indicating their potential for use in recognition. The calls of sibling chicks were similar and chick calls showed greater variability between broods than within broods. In a playback experiment in a water-filled arena, chicks given the choice of parents and non-parents calls preferentially approached the parents calls and responded to them vocally. In two trials, playback of chick calls in a cove containing many adults seeking chicks attracted the correct parents. It is likely that both parents and chicks recognize each others calls and that this ability is based on their experience with the calls prior to departure. The chicks hear their parents calls each time a parent returns to the burrow to relieve its mate. Parents hear the calls of their two chicks after they hatch, a few days before departure. A system of mutual recognition may be fundamental for the success of the colony-departure strategy of ancient murrelets.

Playback: A Historical Perspective

We are here to re-evaluate a technique that has been very productive in the study of animal communication. So in a sense this is a celebration of success. I have been asked to provide a historical overview and, as I look around the room, I see that my grey hair gives me at least one qualification for the task. Playback and I arrived on the scene at about the same time.

FLUCTUATIONS OF DEER MICE IN ONTARIO IN RELATION TO SEED CROPS

We trapped deer mice in Algonquin Park, Ontario, Canada, over a 36-year period. Using information-theoretic methods, we examined relationships among weather variables, sugar maple seed crops, and mouse populations. Deer mouse populations were naturally regulated with stochastic variation in growth rate from year to year influenced strongly by autumn seed crops mediated by temperature during the previous summer and snowfall during the previous winter. Population peaks followed heavy seed crops but did not occur at regular intervals. Demographic characteristics differed between peak and nonpeak populations. Overwinter losses were considerably less entering peak years than in other years. Although overwintered adults were only slightly more numerous in the spring of peak years, they were heavier than in nonpeak years. Breeding began earlier in peak years and in years with high March temperatures. The proportion of young was greater in the spring of peak years but less than in nonpeak years in summer. Apparent survival was greatest in spring and early summer of peak years. Immigration in summer was also greatest in peak years. A combination of the above factors resulted in rapid population growth in spring and early summer of peak years. However, young grew slowly in peak summers and most did not reach breeding mass in contrast to nonpeak years. Breeding was drastically reduced for all sex and age groups in August and September of peak years but continued all summer in nonpeak years. Intensity of late summer breeding was positively related to the current seed crop. Apparent survival declined sharply in late summer of peak years but not in nonpeak years. Thus, declines in breeding and apparent survival were responsible for ending population peaks. We interpret these recurrent events principally as responses to variation in food supply.

Aggressive performance as a behavioral correlate of plumage polymorphism in the white-throated sparrow (Zonotrichia Albicollis)

Morph and sex-specific differences in aggressive performance were examined in the white-throated sparrow. Among the four morph/sex classes, white-striped males had the strongest response to white-striped models and were the most likely to approach and attend song playbacks independently. The slightly weaker responses of tan-striped males and white-striped females were similar to each other. Tan-striped females were the least aggressive. Aggression by white-striped females enabled tan-striped male x white-striped female pairs to perform as well, or better, than white-striped male x tan-striped female pairs. Tan-striped males paired earlier than white-striped males. An increased prevalence of territorial tan-striped males corresponded to the arrival of females on the breeding grounds. The data are consistent with the hypothesis that negative assortative mating benefits tan-striped males through the supplemental aggression of white-striped females. However, the apparent preference of white-striped females for tan-striped males suggests that there are benefits to negative asortative mating other than those that might arise from differences in aggressive performance.

How western meadowlarks classify their songs: evidence from song matching

Abstract Song matching during playback experiments was used to assess how western meadowlarks, Sturnella neglecta, classify variants of their primary song. In separate trials, subjects were played renditions of song types of strangers that they had in their own song repertoires and songs that were similar to their own, but of different types. Birds matched those song types that they had in their own repertoires, but responded to similar songs of different types with song types apparently chosen at random. When half-songs were used as playback stimuli, subjects were able to classify song types correctly using cues present only in the introductory portions of songs. These findings suggest that the song types human observers recognize as ‘natural’ units in the repertoire of this species are also recognized by the birds. A four-level classification of the variation in western meadowlark song is discussed.

Survey techniques and habitat relationships of breeding birds in residential areas of Toronto, Canada

We measured bird abundance and diversity in seven types of residential areas in Toronto, Canada, during the breeding season. We used transects and a combination of nest searching and spot-mapping. Transects underestimated the size for the breeding population for most species. Relationships between the two methods varied between species and residential areas indicating that for several species relative abundance was not directly proportional to breeding density. Several bird species responded similarly to habitat features. Rock Dove (Columbia livid), European Starling (Sturnus vulgaris) and Chimney Swift (Chaetura pelagica) were positively associated with house density and negatively with lawn area. House Sparrow was somewhat different, possibly because they built nests in conifers whenever cavities were absent thus they may not be so dependent on buildings. Another group, including Mourning Dove (Zenaida macroura), American Robin (Turdus migratorius), Common Grackle (Quiscalus quiscula) and Northern Cardinal (Cardinalis cardinalis), all were positively associated with low foliage and lawn area and negatively associated with house density. Other native species (Blue Jay [Cyanocitta cristata], Chipping Sparrow [Spizella passerina], Song Sparrow [Melospiza melodia] and Brown-headed Cowbird [Molothrus ater] shared the same habitat associations as the latter group to a greater or lesser extent. Conifers and shrubs appear to be the two key components linked to species diversity in temperate cities. Our results highlight the duality of the urban bird community structure: 1) the presence of typical urban birds (House Sparrow [Passer domesticus], European Starling, Rock Dove and Chimney Swift) that respond to architectural features first and to natural features second, and 2) the presence of native birds associated with remnant natural features, especially vegetation structure and volume.