Certain inherent characteristics of individuals can determine both physiological and behavioural responses to environmental challenges, which could drive a correlation between levels of corticosterone (CORT), the most important stress hormone and behavioural profiles. Therefore, CORT level may mediate consistent behaviours along the shy/bold continuum, and thus, it could serve as a pleiotropic basis for behavioural syndromes. Moreover, behavioural responses to environmental challenges may have consequences for CORT concentrations, which would also result in a correlation between physiology and behaviours even without requiring pleiotropic mechanisms. Accordingly, we investigated the relationship between CORT and behaviour in free-living male collared flycatchers, Ficedula albicollis, using recently developed field assays. More specifically, we characterised novel object avoidance, intraspecific aggression and risk-taking in males and related these correlated behaviours to the concentration of CORT metabolites in droppings measured by enzyme immunoassay. Individuals with higher levels of excreted CORT metabolites had no consistently higher or lower behavioural scores along the shy/bold spectrum, as avoidance of novelty, aggression and risk-taking were not systematically related to CORT metabolite concentrations in the same direction. Moreover, environmental challenges owing to the presence of a novel object, territorial intruder and a potential predator caused no elevation in the level of CORT metabolites. Therefore, we did not find correlative evidence for CORT driving correlated behaviours through pleiotropic effects or for particular behaviours during courtship causing elevation in CORT levels.

Even for small animals such as spiders, behavioral decisions are sometimes influenced by multiple cues. Orb webs constitute exquisitely precise records of the stimuli the spider experienced and the decisions that it made while building its web. In addition, because spiders appear to sense their webs largely by touch, direct behavioral observations can determine which stimuli they probably sense. Previous studies have shown that when an orb-weaving spider decides how far apart to space successive sticky lines during orb construction, it responds to at least five different kinds of stimuli, all of which apparently use a cue from the web, the location of the previous, inner loop of sticky spiral (IL location), as a point of reference. Here we show that two additional cues from the web, which are related to the position of the temporary spiral (TS), also influence sticky spiral spacing. A combination of direct observations of spider movements, analyses of complete and partially complete webs, and responses to experimental modifications of the web of two species in different families, Micrathena duodecimspinosa (Araneidae) and Leucauge mariana (Tetragnathidae), indicate that both the TS-IL distance itself and the short-term memory of the change in TS-IL distance compared with that on other recently encountered radii correlate with sticky spiral spacing. When the TS-IL distance was large, the spiders apparently ceased to attend to other cues. Thus, even the relatively stereotyped behavior of orb construction includes variation that stems from attention-like mental processes.

Since the 1970s, texts on research methods in animal behavior advocate that researchers minimize potential observer bias in their studies. One way to minimize possible bias is to record or score behavioral data blind to treatment, group, or individual. Another way to reduce bias is for researchers to analyze subsets or entire sets of data independently of one another and to obtain high inter-observer reliability of behavioral coding. We reviewed several hundred published articles from 1970, 1980, 1990, 2000, and 2010 in five leading animal behavior journals and found that these two methods for minimizing or eliminating bias were rarely reported (<10% of articles reviewed). In contrast, a journal focusing on human infant behavior research was far more rigorous in incorporating methods to avoid bias (>80% of articles reviewed). The lack of reporting attempts to minimize bias in animal behavior studies suggests that, at best, many researchers view blind analyses of data or inter-rater reliability as unimportant components of research or, if carried out, unnecessary to report in a manuscript. At worst, the lack of reporting attempts to minimize bias suggests that some published behavioral research may be unreliable. We are aware of constraints imposed by fieldwork and data collecting issues that make blind data comparisons or inter-rater reliability assessments sometimes difficult or unfeasible. However, given that research ethicists often emphasize the fundamental importance of trust and transparency in science, we urge authors, reviewers, and editors of manuscripts to ensure that at least one of these two methods of reducing and reporting observer bias occurs.

Individual personality is an important source of variation in animal behavior. However, few studies have examined the reliability of individual behaviors across both time and context for even common temperament traits such as boldness, especially in mammals. We tested a laboratory colony of Siberian dwarf hamsters (Phodopus sungorus) in two similar assays, a tunnel maze and an open field, both provisioned with a home nestbox for shelter. Animals were tested in each assay at three ages, beginning at weaning. Principal components analysis on each assay identified an axis of activity level in both tests, boldness and reactivity in the tunnel maze, and nestbox orientation in the open field. All traits were moderately (7–18%) heritable. Individual activity level was the most reliably consistent trait, both within and between tests. Tunnel maze boldness, tunnel maze reactivity, and open field nestbox orientation did not correlate at any age. Correlation between boldness and activity changes from positive to negative as animals age, while reactivity was consistently negatively associated with activity. A negative correlation emerged in adults between open field activity and nestbox orientation. These results suggest that either development or habituation results in different personality trait associations in an individual over time. Individual temperament traits such as general activity level may be quite stable, but caution should be used in generalizing single assays to represent boldness across time and across contexts.

Water is essential for all living organisms because it acts as a major solvent and reaction medium. Terrestrial animals may lose water through evaporation and excretion and consequently have evolved strategies to balance their water budget by either minimising losses or by gaining water. The major pathway to gain water is via food intake, although many animals additionally drink free water. Spiders acquire substantial amounts of water by ingesting enzymatically liquefied prey. However, this may not account for the water needs of some species. We tested whether drinking is essential for orb web spiders of the genus Argiope by experimentally manipulating the diet (flies or crickets) and water supply (no water or a daily shower) to females and then measuring their subsequent drinking behaviour. Individuals of Argiope trifasciata, which are typically found in dry habitats, increased their body mass when fed crickets but not when fed flies. However, spiders deprived of water subsequently ingested significantly more water than spiders that received water every day, regardless of their feeding regime. This pattern was replicated in Argiope aetherea, which is found in the tropics and perhaps less likely to be water deprived in natural populations. Our results reveal that drinking allows these spiders to realise their water balance independent from the nutritional status. We suggest that the spiders may need to drink fresh water to process ingested nutrients.

Stable individual differences in activity levels within populations have been linked to differences in reproductive rate or parental care in several species, including American mink (Neovison vison). Fur-farmed mink are good models for studying such effects because they yield large sample sizes and readily allow investigations into maternal behaviour, reproductive success, offspring performance and the relationships between these factors. On farms, very inactive individuals generally have smaller litters, and this held true in our study populations. We tested two competing hypotheses to explain this: (1) inactive individuals are failing to cope with a challenging environment and experiencing chronic stress and/or depression-like ‘apathy’; this predicts female-skewed litters, poorer maternal care, higher infant mortality and poorer infant growth and (2) inactive individuals do not have reduced fitness but instead employ an alternative adaptive reproductive strategy, trading off offspring quantity for quality; this predicts enhanced maternal care, reduced infant mortality and enhanced infant growth. Inactive females’ kits, especially their sons, grew faster than active females’, even after statistically controlling for litter size; and by 21 d, inactive and active dams’ litters no longer differed in total biomass, despite the former’s smaller litter sizes. In kit retrieval tests, inactive females were faster than active dams to reach their sons (as well as more likely to contact their sons than their daughters: a bias towards male kits not evident in the active dams). Furthermore, kit growth rates and dam latencies to touch them co-varied, suggesting the existence of consistent differences in maternal style across inactive and active dams. Hypothesis 2 was thus supported: inactive females favour offspring quality over quantity, investing more resources in fewer kits, particularly males. This potentially boosts their sons’ adult fitness. More broadly for laboratory-based studies, possible ‘captivity effects’ on the fitness correlates of activity and other personality traits are discussed.

The aim of this study was to determine whether geographic variation exists in the composition of note types in the chick-a-dee call of Carolina chickadees. This determination is of interest for two reasons: earlier studies with a related species suggested minimal geographic variation in note composition, and geographic variation in social signals may represent important developmental or selection processes shaping signal use. Carolina chickadees were recorded in a naturalistic observation study in west-central Indiana. Chick-a-dee calls were analyzed and compared to calls from an eastern Tennessee population that had been described in a previously published study (Auk, 125, 2008, 896). Despite much similarity in the basic rules by which notes are organized to compose calls, there were several significant differences in how calls of the two populations were structured. Furthermore, birds from Indiana used their chick-a-dee calls in certain contexts in different ways compared to birds from Tennessee. These findings suggest interesting population-level variation in this call system, and future research should be able to determine whether these differences are driven by evolutionary, ecological, or developmental factors, or some combination of these factors.

Acorn woodpeckers (Melanerpes formicivorus) are cooperative breeders in which groups consist of a variable number of cobreeding males, joint-nesting females, and non-breeding helpers of both sexes that are offspring from prior nests. We temporarily manipulated brood size of nests to determine the feeding response of birds in relation to their status (breeder or non-breeding helper) and sex. All categories of birds responded similarly to brood size increases, adjusting their feeding rate upwards so as to maintain approximately the same per-nestling feeding rate. Breeders, however, exhibited more flexibility with respect to brood size reductions, decreasing their feeding rate while helpers did not. This suggests that the ‘feeding rules’ of helpers are less flexible than those of breeders, a result not previously detected in other cooperative breeders that have been studied to date. Particularly surprising was the finding that helpers maintain their feeding rates when brood demand is decreased rather than when it was increased, suggesting that the flexibility they exhibit is not a result of birds using the opportunity afforded by reduced brood demand to engage in other less cooperative activities.

Many mammal species adopt marking postures that elevate their scent deposits. The most extreme of these is handstand marking, in which an individual reverses against an upright object, flings its hind legs into the air above its back and balances bipedally on its fore feet. The resulting anogenital deposit is thus raised one full body length above ground level. It has been suggested that this energetically costly form of marking serves to provide conspecifics with information about the marker's body size and hence competitive ability. However, this explanation assumes that the height of an individuals’ deposit does reflect accurately its body size, an assumption that has never been tested in any hand-standing species. This study investigated the relationship between body size and handstand mark height in a wild population of dwarf mongooses (Helogale parvula) in South Africa. We found that although body size and marking height were correlated positively for female dwarf mongooses, they were not related for males. Male dwarf mongooses (who are subject to intrasexual competition from outside their group) invested more heavily in anogenital range marking, marking at three times the female frequency and placing their deposits significantly higher than females (although they were not dimorphic). Males that were particularly vulnerable to rivals (i.e. those that were small for their age) tended to mark higher than more robust age-mates, in keeping with the predictions of Adams & Mesterton-Gibbons’ (1995, J. Theor. Biol.175, 405–421). model of deceptive threat communication. These findings suggest strongly that the height of anogenital scent deposits is of social significance to dwarf mongooses.

Demanding performance of vocal signals, such as birdsong, may be evaluated by trade-offs among acoustic traits. If individuals differ in their ability to sustain physiologically demanding singing, then aspects of song performance resulting from such trade-offs could signal individual quality. Song performance can also differ among song types, and it is not known whether this influences the assessment of individual quality. We asked whether three trade-off-based measures of song performance indicate male age or aspects of condition (body condition, hematocrit and ectoparasite load) in the dark-eyed junco (Junco hyemalis), a species with small repertoires. Across a sample of over 100 males, no measure of song performance was related to male age or condition, nor did song performance improve with age for those males recorded in consecutive years. In all cases, the variation in song performance explained by these predictors was small (<4%). Instead, the more song types we recorded from a male, the more likely we were to record high-performance songs, and this sampling effect was stronger than putative correlations with male quality. These results complement a previous study on this population showing that most variation in performance is found among song types rather than among males. Collectively, the lack of association between trade-off-based aspects of song performance and male age or condition, plus variation among song types that interferes with rapid assessment of a male's best performance, indicate that these aspects of song performance do not allow a good assessment of male quality in juncos, and perhaps more generally in species with song repertoires.

In social insects, selection takes place primarily at the level of the colony. Therefore, unlike solitary insects, social species are expected to forage at rates that maximize colony fitness rather than individual fitness. Workers can increase the net benefit of foraging by responding to increased resource availability, by responding more strongly to higher-quality resources, and by decreasing the uncertainty with which nestmates find resources. Unlike many ants and social bees, no social wasp is known to utilize a nest-based recruitment signal to inform nestmates of food location. On the other hand, wasps do learn the odor of food brought to the nest and use this cue to locate the food source outside the nest. Here, we quantify the effects of three food-associated variables on the allocation of foraging effort in the yellowjacket Vespula germanica. We used an experimental approach to assess whether resource quantity, quality, or associated olfactory information affect the probability that a forager will leave the nest on a foraging trip. We addressed these questions by inserting a known amount of sucrose solution directly into nests and recording foraging effort (departure rate) over the subsequent hour-long observation period. No differences were found in foraging effort because of the presence/absence of olfactory cues, but there was strong evidence that foraging effort increased in response to resource influx and resource quality. Thus, while olfactory cues are learned in the nest, only resource quality and the cue of increased amount of food in the nest factor into a forager's decision of whether or not to depart on a foraging trip. However, as prior work has shown, once a wasp forager leaves the nest, it uses the learned olfactory cues to aid in finding resources.