Colleen M. McDonough

Calling and vigilance in California ground squirrels: a test of the tonic communication hypothesis

Owings & Hennessy (1984) proposed that repetitive calling by ground squirrels, i.e. long bouts of calling wherein the same vocalization is uttered repeatedly, might act as a tonic signal to promote vigilance in perceivers. This idea was tested by comparing the effect of naturally occurring repetitive and nonrepetitive calls on the behaviour of California ground squirrels, Spermophilus beecheyi. Both types of calls increased the amount of time spent vigilant by perceivers, especially in bipedal postures. More time was spent vigilant after repetitive than non-repetitive calls, thus supporting the tonic communication hypothesis. However, longer bouts of repetitive calling did not promote proportionately increased vigilance over that evoked by shorter calls. In fact, the reverse was true and the increase in vigilance to repetitive calls began to wane during the later stages of a calling bout. Repetitive calling may represent a case of ‘persuasion’, in which the signaller continues signalling in an attempt to maintain some state in resistant perceivers.

Are Road Kills Valid Indicators of Armadillo Population Structure

-We collected 3 yr of data on road-killed nine-banded armadillos (Dasypus novemcinctus) to determine if these individuals were representative of the population as a whole. Comparisons between road kills and an adjacent live-caught population revealed no differences in sex ratios or the reproductive condition of adult females. However, there was a significant difference in the age structure of the two groups, with almost no juvenile road kills. Our live-caught population appeared representative of armadillo populations in general. Comparisons of the demography of this population with that from two other live-caught groups revealed no significant differences. Our data suggest that road-killed armadillos provide a representative picture of the demography of the adults in a population, but that information on age structure is misleading.

Molecular Documentation of Polyembryony and the Micro-Spatial Dispersion of Clonal Sibships in the Nine-Banded Armadillo, Dasypus novemcinctus

A battery of allelic markers at highly polymorphic microsatellite loci was developed and employed to confirm, genetically, the clonal nature of sibships in nine-banded armadillos. This phenomenon of consistent polyembryony, otherwise nearly unknown among the vertebrates, was capitalized upon to describe the micro-spatial distributions of numerous clonal sibships in a natural population of armadillos. Adult clone mates were significantly more dispersed than were juvenile sibs, suggesting limited opportunities for altruistic behavioural interactions among mature individuals. These results, and considerations of armadillo natural history, suggest that evolutionary explanations for polyembryony in this species may not reside in the kinds of ecological and kin selection theories relevant to some of the polyembryonic invertebrates. Rather, polyembryony in armadillos may be associated evolutionarily with other reproductive peculiarities of the species, including delayed uterine implantation of a single egg.

Genetic maternity and paternity in a local population of armadillos assessed by microsatellite DNA markers and field data.

Genetic data from polymorphic microsatellite loci were employed to estimate paternity and maternity in a local population of nine‐banded armadillos (IDasypus novemcinctus) in northern Florida. The parentage assessments took advantage of maximum likelihood procedures developed expressly for situations when individuals of neither gender can be excluded a priori as candidate parents. The molecular data for 290 individuals, interpreted alone and in conjunction with detailed biological and spatial information for the population, demonstrate high exclusion probabilities and reasonably strong likelihoods of genetic parentage assignment in many cases; low mean probabilities of successful reproductive contribution to the local population by individual armadillo adults in a given year; and statistically significant microspatial associations of parents and their offspring. Results suggest that molecular assays of highly polymorphic genetic systems can add considerable power to assessments of biological parentage in natural populations even when neither parent is otherwise known.

Determinants of aggression in nine-banded armadillos

Potential determinants of aggression in nine-banded armadillos, Dasypus novemcinctus , were identified by comparing the sex, age, and reproductive status of initiators and recipients of aggression in a marked population in southern Texas. Males and females were equally likely to initiate and receive aggression. Adults initiated most aggression, directing it towards younger animals. Adult males directed aggression primarily at 1- and 2-year-old males and did so most frequently during the breeding season (June–November). Most adult males exhibiting aggression were previously or subsequently seen paired with females, suggesting that male aggression may function to maintain exclusive access to receptive females. Adult females directed aggression primarily at juveniles of both sexes and at other adult females, mostly during a 4-month period corresponding to late pregnancy and lactation (February– May). These findings suggest female aggression may function in defending current litters and in promoting the dispersal of last years young. Examination of other potential influences on agonistic behavior showed that heavier individuals were more likely to win encounters and that escalated contests (i.e., fights) were more likely between evenly matched opponents.

Influences on Activity Patterns in a Population of Nine-Banded Armadillos

Patterns of activity and influences on these patterns were examined in a population of nine-banded armadillos ( Dasypus novemcinctus ) from northern Florida, using records of individual sightings during summers 1992–1995. Juveniles were active earlier in the day (i.e., mid-morning to early evening) than were adults. Within each age group, there were no differences in average times of activity between males and females, or between months or years of the study. Comparisons of numbers of individuals observed each hour of the day showed differences in hourly abundances between adults and juveniles and between juvenile males and females, but not between adult males and females. Within each age group, abundances also varied between months and years of the study. The number of animals active at each hour of the day was not evenly distributed for either juveniles or adults. Within each age group, patterning of activity varied across months and between years, although not necessarily for both males and females. Few significant relationships were found between numbers of armadillos observed and environmental conditions when activity across the entire day was considered. However, activity was positively correlated with cloud cover during the day and with drier and warmer conditions at night. Our data suggest considerable flexibility in the timing of activity of armadillos.

Is leprosy spreading among nine-banded armadillos in the southeastern United States?

In the United States, nine-banded armadillo (Dasypus novemcinctus) populations are derived from two sources: (1) a continuous range expansion from Mexico led to western populations, some of which, particularly along the western Gulf Coast and west side of the Mississippi River delta, exhibit persistently high rates of leprosy infection, and (2) a small group of animals released from captivity in Florida gave rise to eastern populations that were all considered leprosy free. Given that western and eastern populations have now merged, an important question becomes, to what extent is leprosy spreading into formerly uninfected populations? To answer this question, we sampled 500 animals from populations in Mississippi, Alabama, and Georgia. Analyses of nuclear microsatellite DNA markers confirmed the historic link between source populations from Texas and Florida, but did not permit resolution of the extent to which these intermediate populations represented eastern versus western gene pools. Prevalence of leprosy was determined by screening blood samples for the presence of antibodies against Mycobacterium leprae and via polymerase chain reaction amplification of armadillo tissues to detect M. leprae DNA. The proportion of infected individuals within each population varied from 0% to 10%. Although rare, a number of positive individuals were identified in eastern sites previously considered uninfected. This indicates leprosy may be spreading eastward and calls into question hypotheses proposing leprosy infection is confined because of ecologic constraints to areas west of the Mississippi River.

Impacts of land management practices on a population of nine-banded armadillos in Northern Florida

Abstract Over a 12-year period (1992–2003), we examined the impact of prescribed burning and hardwood removal on a population of nine-banded armadillos (Dasypus novemcinctus) located at Tall Timbers Research Station just north of Tallahassee, Florida. Although these armadillos are often found in close proximity to humans, there currently are no data on how they are affected by human impacts on the environment. Responses to annual burns between 1992–1997 indicated that in some years armadillos, particularly adults, avoided areas that had been burned, but effects were inconsistent and relatively weak. In contrast, hardwood removal during 1998–2000 coincided with a significant decline in population numbers that continued through 2003. However, interpretation of hardwood removal effects was complicated by the occurrence of a severe drought during the same time period. Comparisons between animals in logged and unlogged parts of the study area during the period of hardwood removal revealed few differences, suggesting drought was an important influence. However, because our population continued to decline after the drought ended, it seems likely that hardwood removal generated more persistent effects that were temporarily masked by the drought. We observed armadillos frequently in logged areas, probably because few other habitat choices were available. Armadillos weighed less during and after hardwood removal than prior to it. Although adult reproductive behavior appeared largely unaffected by logging, numbers of juveniles captured and recruited declined significantly with the onset of hardwood removal. There was no evidence that the disturbance from logging caused increases in distances moved by animals that remained in the study area. Our results may have broader implications for predicting how armadillo populations in Latin America will be affected by similar land management practices.

Spatial Patterns in a Population of Nine-banded Armadillos (Dasypus novemcinctus)

Abstract Spatial data were collected in a population of individually marked nine-banded armadillos (Dasypus novemcinctus) at a site in Florida from 1992–1995. Approximately ⅓ of the animals (118/313) were sighted more than once. Data on distances moved between successive sightings showed that armadillos moved <200 m both within and between years. However, animals moved significantly farther between than within years. The average distance between sightings was significantly longer for adults than for juveniles within, but not between, years. There were no sex differences in distances moved within or between years for either adults or juveniles. Analyses of distances to nearest neighbors showed that adults were closer to one another than to juveniles and that juveniles of the same sex were closer to one another than to juveniles of the opposite sex. This latter result probably reflects maintenance of proximity among littermates.

PAIRING BEHAVIOR OF THE NINE-BANDED ARMADILLO (DASYPUS NOVEMCINCTUS)

-Data on pairing behavior of nine-banded armadillos (Dasypus novemcinctus) were collected for 4 yr in a marked population in S Texas. A pair consisted of a male and female maintaining proximity (<10 m) without aggression, pairing behavior involved those behaviors exhibited during this interaction. Some of these behaviors were only observed during pairing. Males were responsible for maintaining proximity to females through repeated approaches and by monitoring their surroundings for the location or movement of the female (i.e., exhibiting vigilance). The incidences of some behaviors were significantly associated with others, specifically dorsal touches by males elicited tail-wagging by females. Tail-wagging probably facilitated the transmission of olfactory information about female receptivity. After tail-wagging the male was more likely to contact and sniff. Contacts, which occurred in every pairing event were positively correlated with sniffs and tail-wagging and might be used as an index of receptivity. Pairing behavior apparently generated a cost of reduced foraging time for males by increasing their vigilance levels.