Walter H. Piper

Making habitat selection more “familiar”: a review

Behavioral ecologists generally agree that animals derive benefits from familiarity with spaces that they inhabit or visit, yet site familiarity is rudimentary or lacking in most models of habitat selection. In this review, I examine evidence for the occurrence of site familiarity and its fitness benefits, describe the difficulty of measuring site familiarity, note its omission from the influential ideal free and ideal despotic models, and use a literature search to test an assumption of the ideal models that has become widespread in habitat selection theory: that animals behave without regard for site familiarity. I find little support for such “familiarity blindness” in vertebrates. Next I discuss how the study of public information has drawn attention away from site familiarity and point out that both kinds of information are likely to be important in habitat selection. I proceed to examine current models of initial settlement (exploration and settlement of prebreeders on first territories) and optional resettlement (site fidelity or dispersal by established breeders following a period of prospecting) and find that the latter include only basic forms of site familiarity. Hence, I develop the concept that an inhabited space holds a unique “private value” to an animal based on its familiarity with the space and offer a simple model for optional resettlement based on private value that generates several novel predictions, including site fidelity based on cumulative breeding site familiarity and high site fidelity among species with complex territories.

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.

Common Loon Survival Rates and Mercury in New England and Wisconsin

Abstract Bioaccumulation of toxic environmental mercury may affect the vital rates of piscivores such as the common loon (Gavia immer). Although immediate effects of mercury on early development or reproduction can be determined from short-term field studies or dosing experiments, long-term effects on survival for a long-lived species such as the common loon must be discerned from large, long-term observational data sets. We analyzed band-resight and mercury data for 776 adult loons in Wisconsin and New England, USA, from 1991 to 2001 to 1) estimate annual survival rates and 2) investigate the relation between mercury exposure and survival. The model-averaged estimate of apparent survival was 0.87, whereas the approximate survival rate (accounting for movement) was 0.92. We found no differences in apparent survival by geographic location or sex and no relation between survival and mercury. Power analyses showed that we were only likely to detect differences in survival ≥3%. Small differences in survival (<3%), which may be important to loon population viability, were unlikely to be detected in our dataset.

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 residents 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.

Does breeding density covary with extra-pair fertilizations in Hooded Warblers?

The extent of variation in the frequency of extra-pair matings among and within avian species could result from differences in breeding density, where breeding density is predicted to be positively correlated with extra-pair paternity. We combined paternity data and behavioural observations to evaluate this prediction using correlational data in relation to observed densities of Hooded Warblers Wilsonia citrina by comparing populations differing in (1) nearest neighbour distance which varied by more than an order of magnitude (range 50-600 m) and (2) the number of adjacent neighbours within 300 m (range 0-8). Spearman rank correlations demonstrated no relationship between extra-pair paternity and either inter-territory distance or the number of adjacent neighbours within 300 m. The rate of extra-territorial forays, female chip rates, the number of chipping bouts, time spent chipping, male song rates, the number of song bouts and time spent singing were similar among pairs breeding at different densities. Our results suggest that a simple linear relationship between density and extra-pair paternity may not exist in some avian species, possibly because the costs of inter-territory travel may be much lower than the benefits gained through extra-pair fertilizations, and also because of the conflicting mating tactics used by males and females.

Local Movements of Color-Marked Common Loons

We studied movement of color-marked common loons (Gavia immer) among small lakes (4-349 ha) in northern Wisconsin and the Upper Peninsula of Michigan to determine the frequency, timing, and ecological causes of multiple-lake usage. Most instances of multiple-lake usage fell into 1 of 5 categories: (1) territorial defense of 2 or more lakes by a breeding pair, (2) post-reproductive wandering, (3) territorial shifts prior to breeding, (4) dispersal of displaced breeders, or (5) long-distance movements by young birds. Overall, distances moved by adult loons between lakes were shorter than expected. The frequency of such movements might indicate reconnaissance for new territories, consistent with the frequent territorial takeover observed in this species. Regular use by loons of small clusters of lakes suggests that a management strategy that preserves only small, isolated breeding lakes might be inadequate to sustain nesting pairs and also might hamper natural dispersal between lakes.

Floating platforms increase reproductive success of common loons

Many southern populations of the common loon (Gavia immer) face threats from lead and methylmercury contamination, lake acidification, shoreline development and human recreation. It is now clear that the task of conserving loon populations will depend upon mitigating these varied threats. In a controlled experiment, we examined the efficacy of using floating nest platforms to increase reproductive success of loons and thus help sustain local populations. Platforms were attractive nesting sites both on lakes that had consistently hatched chicks from natural sites and on lakes where chick production had been sporadic. When compared to natural nest sites, platforms increased hatching success by 69% and fledging success by 32%, apparently through reduction in mammalian egg predation. A well-managed effort to introduce nesting platforms might be a viable strategy to help sustain threatened populations.

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.

Population Growth and Demography of Common Loons in the Northern United States

Abstract We used recent developments in theoretical population ecology to construct basic models of common loon (Gavia immer) demography and population dynamics. We parameterized these models using existing survival estimates and data from long-term monitoring of loon productivity and abundance. Our models include deterministic, 2-stage, density-independent matrix models, yielding population growth-rate estimates (λ) of 0.99 and 1.01 for intensively studied populations in our Wisconsin, USA, and New Hampshire, USA, study areas, respectively. Perturbation analysis of these models indicated that estimated growth rate is extremely sensitive to adult survival, as expected for this long-lived species. Also, we examined 20 years of count data for the 2 areas and evaluated support for a set of count-based models of population growth. We detected no temporal trend in Wisconsin, which would be consistent with fluctuation around an average equilibrium state but could also result from data limitations. For New Hampshire, the model set included varying formulations of density dependence and partitioning of stochasticity that were enabled by the annual sampling resolution. The best model for New Hampshire included density regulation of population growth and, along with the demographic analyses for both areas, provided insight into the possible importance of breeding habitat availability and the abundance of nonbreeding adults. Based on these results, we recommend that conservation organizations include nonbreeder abundance in common loon monitoring efforts and that additional emphasis be placed on identifying and managing human influences on adult loon survival.

Can settlement in natal-like habitat explain maladaptive habitat selection?

The study of habitat selection has long been influenced by the ideal free model, which maintains that young adults settle in habitat according to its inherent quality and the density of conspecifics within it. The model has gained support in recent years from the finding that conspecifics produce cues inadvertently that help prebreeders locate good habitat. Yet abundant evidence shows that animals often fail to occupy habitats that ecologists have identified as those of highest quality, leading to the conclusion that young animals settle on breeding spaces by means not widely understood. Here, we report that a phenomenon virtually unknown in nature, natal habitat preference induction (NHPI), is a strong predictor of territory settlement in both male and female common loons (Gavia immer). NHPI causes young animals to settle on natal-like breeding spaces, but not necessarily those that maximize reproductive success. If widespread, NHPI might explain apparently maladaptive habitat settlement.