Male Common Loons Research Articles

Dynamics of an Aggressive Vocalization in the Common Loon (Gavia immer): A Review

Unlike most waterbirds, Common Loons (Gavia immer) have a dynamic vocal repertoire that includes the high-amplitude wail, tremolo, and yodel. This paper is a review of the acoustic structure of the yodel, an aggressive warning signal only given by male Common Loons. The context in which males yodel is described along with the possible adaptive functions of this signal. The yodel is the most acoustically complex vocalization of the Common Loon and contains a wealth of information about the signaler. Suites of frequency and time elements of the yodel appear to communicate information about the identity of the signaler, which may be important for neighbor-stranger, mate, and kin recognition. The peak frequencies of the final note of the introductory phrase and repeat phrases also appear to communicate the condition-dependent fighting ability. Finally, the number of repeat phrases a male adds to its yodel appears to communicate the aggressive motivation, or the willingness a male Common Loon has to escalate a contest. Under various contexts not necessarily unique to Common Loons, these functions may be mutually beneficial to signalers and conspecific and heterospecific receivers, and evoke a number of interesting questions regarding the function of this dynamic signal. Such dynamic vocal signals are rare among waterbirds, and among ornithologists and behaviorists alike elicit questions regarding the conditions that maintain signal honesty among birds communicating fighting ability and aggressive state within the same vocal signal.

The Impact of Mercury Exposure on the Common Loon (Gavia immer) Population in the Adirondack Park, New York, USA

The Common Loon (Gavia immer), a top trophic-level piscivorous predator, was used as an indicator species to assess mercury exposure and risk in aquatic ecosystems in the Adirondack Park of New York State. Mercury levels in Common Loons were related to long-term reproductive success to evaluate the effects of mercury contamination on the breeding population in the Park and enable the development of a mercury hazard profile. Common Loons were sampled and monitored on selected study lakes from 1998–2007. Lake acidity correlated with Common Loon mercury levels, with more acidic lakes exhibiting higher mercury concentrations in Common Loons. Based on mercury body burden estimated by blood mercury exposure, 21% of males and 8% of females were at high risk for behavioral and reproductive impacts, while feather mercury exposure estimated that 37% of males and 7% of females were at high risk. Female and male Common Loons in the highest exposure category showed a 32% and 56% reduction, respectively, in the number of chicks fledged per year, compared to individuals in the lowest exposure category. Thirteen percent of the Adirondack Common Loon eggs sampled were at high risk for mercury exposure. Population model results indicated that the portion of the Adirondack Common Loon population with high mercury levels has a reduced growth rate (λ = 1.0005), compared to Common Loons with low body burdens of mercury (λ = 1.026). The results of this project will assist in the continued refinement of State and Federal policies and regulations that effectively address the ecological impacts mercury and other environmental contaminants pose to freshwater ecosystems. Received 21 January 2013, accepted 26 May 2013.

Male Common Loons Signal Greater Aggressive Motivation By Lengthening Territorial Yodels

Abstract We examined two critical predictions of the hypothesis that male Common Loons (Gavia immer) communicate greater aggressive motivation by increasing the number of repeat syllables within their territorial yodels. We observed (from >3,500 hrs of field observations of 58 males) the probability that territorial interactions escalated from territorial flyovers by intruders to stereotyped ‘social gatherings’ to escalated fights between residents and intruders was positively correlated to the number of repeat syllables given by individually-banded males. Males yodeling during these escalated contests often assumed the upright ‘vulture’ posture rather than the usual ‘crouch’ posture, reflecting an escalated aggressive motivational state. Territorial pairs responded sooner and with more threat and alarm vocalizations to playback yodels that contained more repeat phrases. This reflected a greater willingness to attack by residents to perceived intrusions by males of higher aggressive motivational state. Ou...

Fatal battles in common loons: a preliminary analysis

Theoretical models predict that lethal contests should take place only when animals have severely limited breeding opportunities. Indeed, fatal fighting appears to occur routinely in only a handful of species that fit this mould. Here we report that 16–33% of all territorial evictions in male common loons, Gavia immer, are fatal for the displaced owner; in contrast, females seldom fight to the death for territories despite frequent territorial evictions. Since loons are long-lived and have ample reproductive options, they differ starkly from other fatal-fighting species. Several factors might contribute to lethal combat in loons, including: (1) the high value of territories to males, (2) a steady loss of condition among male residents, which could lead individuals with poor reproductive prospects to invest heavily in a current reproductive attempt, and (3) an inability of males defending tiny lakes to escape aggressive usurpers, owing to extremely high wing loading. The difficulty of detecting fatal contests in the field and the tendency of scientists to underestimate the behavioural impact of rare events leave open the possibility that fatal contests are a more widespread behavioural pattern than currently thought.

Nestsite selection by male loons leads to sex‐biased site familiarity

1. The concept that animals benefit from gaining familiarity with physical spaces is widespread among ecologists and constitutes a theoretical pillar in studies of territory defence, philopatry and habitat selection. Yet proximate causes and fitness benefits of site familiarity are poorly known. 2. We used data from marked common loons Gavia immer breeding on 98 territories over 14 years to investigate the 'win-stay, lose-switch rule' for nestsite placement (if eggs hatch, reuse nestsite; if predator takes eggs, move nestsite). Males controlled nest placement in this species: pairs used the rule if both members remained the same from the previous nesting attempt or if only the male remained the same but not if only the female remained the same. 3. By means of the nesting rule, male common loons benefited from site familiarity, increasing nesting success by 41% between their first and third years on a territory. In contrast, females exhibited no increase in nesting success with increased territorial tenure. 4. Owing to site familiarity, a male loon competing for a breeding territory faces a considerable 'familiarity deficit' compared with the male breeder already established there. The familiarity deficit probably explains why resident animals often fight hard to retain familiar territories, when challenged, and why animals of many species tend to remain on familiar territories rather than moving when territories of higher intrinsic quality become available nearby.

Nest platforms increase aggressive behavior in common loons

Artificial manipulations of habitat, such as those that incorporate adding nesting boxes or platforms for birds, often enhance the breeding success of threatened animals. However, such alterations are likely to have unintended behavioral and ecological effects that might negatively impact the target species or others in its community. We conducted a controlled study to investigate the effect of artificial nesting platforms on aggressive behavior and reproductive success of male common loons (Gavia immer). Males residing on territories to which platforms were added produced longer territorial "yodels" (reflecting willingness to escalate a contest), experienced increased levels of confrontation and aggression with territorial intruders, and experienced increased rates of territorial displacement by intruders. Surprisingly, males of treatment territories also experienced lower productivity. Therefore, in addition to providing novel empirical support of sequential assessment models of animal contests that predict contest escalation with increasing resource quality, this study is one of a few to show that tools used to mitigate habitat loss can negatively impact reproductive fitness in a threatened species.

Male common loons, Gavia immer, communicate body mass and condition through dominant frequencies of territorial yodels

We investigated whether male-specific territorial ‘yodels’ communicate information about individual size and condition in the common loon. Individuals in better condition and of larger body mass, but not larger structural body size, produced lower-frequency yodels, and changes in dominant frequencies of yodels between years reflected changes in male body mass and condition. An acoustic playback experiment indicated that potential receivers vocalized sooner and more often in response to low-frequency yodels, a possible indication that dominant frequencies of the yodel may communicate condition-dependent fighting abilities. Physiological constraints associated with mass and/or condition may preserve honest signalling by preventing small individuals from producing low-frequency yodels.

Macrogeographic Variation in the Body Size and Territorial Vocalizations of Male Common Loons (Gavia immer)

Abstract Geographic variation in the body mass and acoustic parameters of territorial ‘yodels’ recorded from male Common Loons (Gavia immer) were assessed for individuals breeding on territories across the eastern United States. Multivariate analyses incorporating male body mass, body size, the acoustic parameters of yodels, and geographic latitude and longitude indicated that males inhabiting lakes in northwestern regions were smaller and produced higher-frequency yodels. These relationships strengthen previous observations of clinal geographic variation in loon body size and vocal behavior across North America, but also support the hypothesis that the dominant frequencies of yodels are in part influenced by male body size. Therefore, the frequencies loons use for long-distance communication are apparently influenced, at least in part, by those selective forces responsible for shaping optimal body size.

Changing territories, changing tunes: male loons, Gavia immer, change their vocalizations when they change territories

Male common loons produce a territorial vocalization called the yodel. Each male loon has a characteristic yodel that is stable from year to year and differs from that of other male loons on other lakes. Of 13 male loons whose yodels we recorded before and after they changed territories, 12 substantially changed their yodels either the first or second year on the new territory. Furthermore, this change increased the difference between the new resident's yodel and that of the previous resident. This result implies that loons not only change their vocalizations as the birds change territory, but also that the new owner is familiar with the yodel of the resident that it replaces.

Relating Land Cover Characteristics and Common Loon Mercury Levels Using Geographic Information Systems

This effort models the relationship between mercury (Hg) levels in the common loon (Gavia immer) and land cover types as defined by the National Land Cover Database (NLCD). We constructed the model within the framework of a GIS to analyze the spatial relationships between land cover types and blood Hg levels in male common loons. Thiessan polygons were used to generate the territory for each loon. We created 150, 300, and 600-m buffers around the Thiessan polygons and modeled the relationships that existed in each distance class. Within the 150-m buffer, three cover types, crop land, shrub land, and wetland were significantly related to blood Hg levels (r2 = 0.552, p < 0.001), which may indicate that the proximity of these cover types influences Hg availability in loon territories. Cropland exhibited a negative relationship with blood Hg levels and may play a role in reducing the amount of available Hg within the study area while wetlands and shrub lands exhibit a positive relationship. The study area consisted of five major lakes and eleven smaller ponds in northwest Maine, and data included a total of 61 male common loon blood Hg samples.

INDIVIDUALITY IN “YODEL” CALLS RECORDED FROM A BANDED POPULATION OF COMMON LOONS, GAVIA IMMER

ABSTRACT Male common loons, Gavia immer, produce a territorial vocalization called the yodel. We quantitatively examined yodels using discriminant and cross correlation analysis. Both techniques correctly assigned the majority of the male's yodels to the proper group, however discriminant analysis was more accurate for making long term comparisons of a yodel's stability. Of four male loons in a color marked, breeding population at the Seney National Wildlife Refuge in Michigan, each male's yodel was different and these differences were maintained over the six years of this study. There is a suggestion that changes in the yodel may be related to territory and mate switching, indicating that individuality in the yodel may be linked to female choice.