Dynamic Status Signal Reflects Outcome of Social Interactions, but Not Energetic Stress

Social defeat induces stress-responses in a wide array of vertebrates and can generate winner-loser effects. Dynamic condition-dependent signaling systems that reflect preparation for subsequent agonistic interactions, and thereby mediate winner-loser effects, should be more sensitive to competitive history than to non-social sources of stress. Bill color of female American goldfinches (Spinus tristus) is a dynamic condition-dependent ornament that functions as a signal of competitive status and mediates intrasexual agonistic social interactions. We tested the “social experience signaling hypothesis” in female goldfinches by (1) manipulating a non-social energetic stressor by experimentally elevating flight costs via wing-clipping in free-ranging birds, and (2) manipulating social experience by staging competitive interactions among captive birds. Bill color change did not differ between wing clipped and non-clipped females, even though stress-response, as measured by the heterophil to lymphocyte (H:L) ratio, increased significantly in clipped females relative to unclipped females. In contrast, winners and losers in the social experience experiment differed significantly in the degree and direction of bill color change following social contests, with bill color increasing in winners and decreasing in losers. These results suggest that dynamic bill color of female American goldfinches signals recent social history, but is less sensitive to some stressors stemming from non-social sources, and thereby suggest that signals can evolve sensitivity to specific types of processes relevant to the context in which they are used

Same Trait, Different Receiver Response: Unlike Females, Male American Goldfinches Do Not Signal Status with Bill Colour

In species in which both sexes have similar ornamentation, the ornaments often function as sexual or social signals in both sexes. However, males and females may use ornaments in different signalling contexts. We previously demonstrated that carotenoid-based bill colour of female American goldfinches, Spinus tristis, functions as a signal of status during intrasexual, but not intersexual, competition. Here we test whether male bill colour functions as a competitive status signal during both intra- and intersexual contests. We tested whether focal males and females avoided feeding adjacent to taxidermic male models as a function of the models’ experimentally altered bill colour. We additionally tested whether male bill colour functions as a mate choice signal by presenting females with a choice of two live males with experimentally altered bill colour. In the status signal experiment, neither focal males nor females avoided male models with more colourful bills, as was predicted by the status-signalling hypothesis. These results indicate that male bill coloration does not function as a signal of competitive status and that the signal function of male bill colour does not parallel that of female bill colour. In our mate choice experiment, females showed no preference for male bill colour, suggesting that male bill colour may have some yet untested signalling function or that male bill colour may no longer be under selection. Our findings suggest that selection can lead to different signalling strategies in males and females, even in species that express mutual ornamentation

Multiple hypotheses explain variation in extra-pair paternity at different levels in a single bird family

Extra‐pair paternity (EPP), where offspring are sired by a male other than the social male, varies enormously both within and among species. Trying to explain this variation has proved difficult because the majority of the interspecific variation is phylogenetically based. Ideally, variation in EPP should be investigated in closely related species, but clades with sufficient variation are rare. We present a comprehensive multifactorial test to explain variation in EPP among individuals in 20 populations of nine species over 89 years from a single bird family (Maluridae). Females had higher EPP in the presence of more helpers, more neighbours or if paired incestuously. Furthermore, higher EPP occurred in years with many incestuous pairs, populations with many helpers and species with high male density or in which males provide less care. Altogether, these variables accounted for 48% of the total and 89% of the interspecific and interpopulation variation in EPP. These findings indicate why consistent patterns in EPP have been so challenging to detect and suggest that a single predictor is unlikely to account for the enormous variation in EPP across levels of analysis. Nevertheless, it also shows that existing hypotheses can explain the variation in EPP well and that the density of males in particular is a good predictor to explain variation in EPP among species when a large part of the confounding effect of phylogeny is excluded

Monk Parakeets In The United States: Population Growth And Regional Patterns Of Distribution

Records from Christmas Bird Counts were summarized to assess population growth of the Monk Parakeet (Myiopsitta monachus) in the United States from 1975 to 1996. Population growth over this period fits an exponential model of population growth with a current annual rate of increase of 12.9% and a doubling time of 5.4 years. Since 1990, however, population growth on a national scale has slowed considerably, suggesting that the species may be approaching a carrying capacity. In contrast to the results across the entire United States, the population of Monk Parakeets in northeastern Illinois has dramatically increased in numbers within the last decade. In this region, the Hyde Park, Chicago population appears to be acting as a source from which other areas are colonized. The Monk Parakeet is known to have caused damage to fruit crops in Florida, and they can be a nuisance species to local utility companies when they build their nests on power transformers. Nevertheless, such damage is highly localized and, on a national scale, there is no evidence to date that Monk Parakeets should be considered a pest species and subject to widespread control. The initiation of detailed studies of a banded population of this species is recommended

Monk parakeets in the Unites States: population growth and regional patterns of distrubution

Records from Christmas Bird Counts were summarized to assess population growth of the Monk parakeet (Myiopsitta monachus) in the United States from 1975 to 1996. Population growth over this period fits an exponential model of population growth with a current annual rate of increase of 12.9% and a doubling time of 5.4 years. Since 1990, however, population growth on a national scale has slowed considerably, suggesting that the species may be approaching a carrying capacity. In contrast to the results across the entire United States, the population of monk parakeets in northeastern Illinois has dramatically increased in numbers within the last decade. In this region, the Hyde Park, Chicago population appears to be acting as a source from which other areas are colonized. The monk parakeet is known to have caused damage to fruit crops in Florida, and they can be a nuisance species to local utility companies when they build their nests on power transformers. Nevertheless, such damage is highly localized and, on a national scale, there is no evidence to date that monk parakeets should be considered a pest species and subject to widespread control. The initiation of detailed studies of a banded population of this species is recommende

Male zebrafish (Danio rerio) do not preferentially associate with familiar over unfamiliar conspecifics

Members of several shoaling species have been shown to prefer to associate with familiar individuals, enhancing the benefits of aggregation. The authors used a series of social preference tasks in the laboratory to evaluate whether prior familiarity with potential partners influences preference of shoaling partner in male zebrafish (Danio rerio), a social species found in shallow, slow-moving waters. The authors found that though male zebrafish exhibited a strong preference for shoaling with a male conspecific as opposed to remaining alone, they exhibited no preference for familiar over unfamiliar conspecifics. This suggests that the benefits of familiarity for shoaling behaviour may not be as important for male zebrafish as has been shown in other social fish species