Tom A. Langen

How do animals choose their mates

How animals search for and evaluate prospective mates has, until recently, been a neglected aspect of sexual selection. Theory and field data suggest that discrimination varies with the costs and benefits of choice, but a consensus has yet to be reached on the tactics by which prospective mates are evaluated. This intriguing issue may be clarified by new studies that deal explicitly with the process of information acquisition.

Evolution of correlated characters

Many traits are genetically correlated with each other. Thus, selection that changes the mean value of one trait causes other traits to change as well. Recent comparative studies have emphasized the possible importance of such correlated responses in affecting the evolution of traits, including some behaviors, which are of little adaptive significance, or even maladaptive. However, it is also possible for traits with major effects on fitness, such as brain size, to evolve entirely by correlated response. Other traits that do not appear to have evolved at all may have been subject to much directional selection, simply to prevent their evolution by correlated response. The new interest in correlated responses reflects more rigorous attempts to consider the organism as a whole, rather than dissecting it into a number of questionably separable traits.

The red and the black: habituation and the dear-enemy phenomenon in two desert Pheidole ants

Abstract Many species of territorial animals are more aggressive toward strangers than neighbors, a pattern of aggression referred to as the ’dear-enemy phenomenon.’ In many cases, the mechanism by which neighbors are discriminated from strangers and the function of neighbor-stranger discrimination remain controversial. We investigated the spatial patterns of inter-colony aggression within and between two Pheidole species of seed-harvesting ants in the Mojave Desert of California by quantifying aggression between colonies in standardized staged encounters. We also tested whether the level of fighting between workers of two colonies is affected by previous exposure to each other. We show that neighbors (i.e., colonies less that 2.6 m away) of either species are treated less aggressively than more distant colonies and that habituation may be a mechanism by which this discrimination is achieved. The variation in aggression among spatially distant colonies also suggests that additional genetic or environmental factors are involved in recognition. The function of the dear-enemy phenomenon in these ant species may be related to the greater risk to the resources of a colony presented by strange workers than workers from a neighboring colony.

Predicting hot spots of herpetofauna road mortality along highway networks.

Abstract Road mortality is often spatially aggregated, and there is a need for models that accurately and efficiently predict hot spots within a road network for mitigation. We surveyed 145 points throughout a 353-km highway network in New York State, USA, for roadkill of reptiles and amphibians. We used land cover, wetland configuration, and traffic volume data to identify features that best predicted hot spots of herpetofauna road mortality. We resampled 40 points an additional 4 times over 4 years to evaluate temporal repeatability. Both amphibian and reptile road mortality were spatially clustered, and road-kill hot spots of the 2 taxa overlapped. One survey provided a valid snapshot of spatial patterns of road mortality, and spatial patterns remained stable across time. Road-kill hot spots were located where wetlands approached within 100 m of the road, and the best predictor was a causeway configuration of wetlands (wetlands on both sides of the road). We validated causeways as predictors of road mortality by surveying 180 causeways and 180 random points across 5 regions (17,823 km2) of northeastern New York. Causeways were 3 times more likely than random locations to have amphibian and 12 times more likely to have reptile mortality present, and causeways had a 4 times higher total number of amphibian roadkill and 9 times higher reptile roadkill than did random points. We conclude it is possible to identify valid predictors of hot spots of amphibian and reptile road mortality for use when planning roads or when conducting surveys on existing roads to locate priority areas for mitigation.

Methodologies for Surveying Herpetofauna Mortality on Rural Highways

Abstract Road mortality can contribute to local and regional declines in amphibian and reptile populations. Thus, there is a need to accurately and efficiently identify hotspots of road-mortality for hazard assessment and mitigation. In 2002, we conducted walking and driving surveys throughout an extensive rural highway network in northern New York, USA, to evaluate survey methods and to quantify spatial and temporal patterns of herpetofauna road-mortality. In 2004, we repeated the surveys at a subset of locations to quantify interannual repeatability. Reptile and amphibian species had different peak periods of road-mortality because they differed in the causes of movements that resulted in crossings. Spatial locations of herpetofauna road-mortality were concentrated at a limited number of hotspots. Hotspots overlapped across species and were located at consistent locations across years. Results of walking and driving surveys were highly repeatable among survey teams, but driving surveys underestimated the density of road-mortality because many animals were missed. Detection failure was higher in some taxa (e.g., frogs) than others (e.g., turtles). Our results indicate that it is possible to design a valid, efficient methodology for locating hotspots of reptile and amphibian road-mortality along a road network and, thus, pinpoint priority sites for mitigation.

Ecological factors affecting group and territory size in white-throated Magpie-Jays

White-throated Magpie-Jays (Calocitta formosa) breed cooperatively and de- fend permanent, all-purpose group territories. We measured territory area, resource levels, resource dispersion, group size, and group reproductive success for 14 groups over a three- year period in Costa Rica. Larger groups possessed larger territories containing more bull- horn acacia trees (Acacia cornigera and A. collinsii), which provided a critical food resource during the dry season. On a per capita basis, however, the number of acacia trees and ter- ritory area were the same for group members regardless of group size, and survivorship did not vary significantly with group size. Variation in reproductive success among groups was influenced by two factors: (1) larger groups produced more successful nests per year, and (2) territories with a higher density of acacia trees fledged more offspring per successful nest. Magpie-jays bred in pasture and foraged primarily in woodland; both habitat types were patchily distributed. The dispersion of woodland and pasture patches in the landscape ap- peared to constrain where jays could form territories, whereas the amount of acacia and other food resources determined the size that groups could attain. We conclude that ecolog- ical factors are critical to understanding the White-throated Magpie-Jay social system, along with other social and demographic constraints typically found in avian cooperative breed- ers. Received 4 February 1997, accepted 20 August 1997.

Skill acquisition and the timing of natal dispersal in the white-throated magpie-jay, Calocitta formosa

Abstract Offspring may remain associated with parents to gain the skills required for independent survival and reproduction. The ontogeny of foraging and breeding behaviour was followed in a cohort of cooperatively breeding white-throated magpie-jays from fledging through to dispersal. Young jays approached adult levels of foraging proficiency within 1 year of fledging. During their first year of age, young jays provisioned nests as helpers at a lower rate than did older individuals. No improvement occurred during that first year, however, suggesting that lower provisioning was the result of other factors than the lack of foraging or nesting skills. Natal dispersal was extremely sex-biased: males dispersed between 4 and 23 months of age, but females remained in their natal group. Male dispersal coincided with both the maturation of foraging skills and the start of a breeding season. Males from larger groups dispersed at an earlier age than those from smaller groups. Therefore, although offspring must associate with parents during some minimum period to acquire skills, the decision of whether and when to disperse from the natal territory is determined by other factors in the white-throated magpie-jay.

Predation on artificial bird nests in chaparral fragments

SummaryThe predation rate of artificial bird nests was measured in disturbed chaparral habitat fragments and at an unfragmented site in coastal San Diego County, California USA. Local extinctions of chaparral birds has been previously shown to occur in these fragments. The predation rate was highest at the unfragmented site. Among fragments, predation was higher at moderately disturbed than at highly disturbed sites. These results suggest that nest predator species diversity or density is reduced in disturbed chaparral fragments. Nest predation is probably not the most important cause of the observed loss of chaparral breeding bird diversity in these fragments.

Comparing alternative models to empirical data: Cognitive models of western scrub-jay foraging behavior

Animals often select one item from a set of candidates, as when choosing a foraging site or mate, and are expected to possess accurate and efficient rules for acquiring information and making decisions. Little is known, however, about the decision rules animals use. We compare patterns of information sampling by western scrub‐jays (Aphelocoma californica) when choosing a nut with three decision rules: best of n (BN), flexible threshold (FT), and comparative Bayes (CB). First, we use a null hypothesis testing approach and find that the CB decision rule, in which individuals use past experiences to make nonrandom assessment and choice decisions, produces patterns of behavior that more closely correspond to observed patterns of nut sampling in scrub‐jays than the other two rules. This approach does not allow us to quantify how much better CB is at predicting scrub‐jay behavior than the other decision rules. Second, we use a model selection approach that uses Akaike Information Criteria to quantify how well alternative models approximate observed data. We find that the CB rule is much more likely to produce the observed patterns of scrub‐jay behavior than the other rules. This result provides some of the best empirical evidence of the use of Bayesian information updating by a nonhuman animal.

Reverse sex‐biased philopatry in a cooperative bird: genetic consequences and a social cause

The genetic structure of a group or population of organisms can profoundly influence the potential for inbreeding and, through this, can affect both dispersal strategies and mating systems. We used estimates of genetic relatedness as well as likelihood‐based methods to reconstruct social group composition and examine sex biases in dispersal in a Costa Rican population of white‐throated magpie‐jays (Calocitta formosa, Swainson 1827), one of the few birds suggested to have female‐biased natal philopatry. We found that females within groups were more closely related than males, which is consistent with observational data indicating that males disperse upon maturity, whereas females tend to remain in their natal territories and act as helpers. In addition, males were generally unrelated to one another within groups, suggesting that males do not disperse with or towards relatives. Finally, within social groups, female helpers were less related to male than female breeders, suggesting greater male turnover within groups. This last result indicates that within the natal group, female offspring have more opportunities than males to mate with nonrelatives, which might help to explain the unusual pattern of female‐biased philopatry and male‐biased dispersal in this system. We suggest that the novel approach adopted here is likely to be particularly useful for short‐term studies or those conducted on rare or difficult‐to‐observe species, as it allows one to establish general patterns of philopatry and genetic structure without the need for long‐term monitoring of identifiable individuals.