Winter circadian activity pattern of free-ranging coypus in the Paraná River Delta, eastern Argentina

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Winter circadian activity pattern of free-ranging coypus in the Paraná River Delta, eastern Argentina

Francisco PALOMARES, Roberto BO, Juan F. BELTRAN,

Gloria VILLAFAE and Sacramento MORENO

Palomares F., Bo R., Beltrdn J. F’., VillafaSe (1. and Moreno S. 1994. Winter circadian activity pattern of free-ranging coypus in the Paraná River Delta, eastern Argentina. Ada theriol. 39: 83—88.

During August 1990, 3 male and 3 female coypus Myocastor coypus (Molina, 1782) were radiotracked for 42 24-h periods at the Delta of Parand River, Argentina. Coypus were mainly nocturnal, with activity peaks around one hour after sunset and two hours before sunrise. Movement rate peaked between 02.00 and 04.00 o’clock. This pattern is similar to that observed in captive individuals and introduced feral popu­ lations. Among 7 environmental factors (day period, temperature, wind, cloud cover, and presence or absence of moon, fog, and rain) only period of day and rainfall during daylight were found significantly related to coypu activity, but no environmental factor influenced coypu nocturnal rate of movement.
Estacidn Biolégica Donana, OSlO, Apartado 10t6, 41080 Sevilla, Spain (FP, JFB, SM); G.E.S.E.R. Fac. de Cs. Ex. y Naturales, University of Buenos Aires, Ciudad Univer­ sitaria, Pab. IT- Dpto. de Cs. Biológieas, 1423 Buenos Aires, Argentina (RB, GV)
Key words: Myocastor coypus, activity pattern, distance travelled, Argentina

The coypu or nutria Myocastor coypus (Molina, 1782) is a rodent indigenous to

South America and an appreciated economic resource as ifirbearer (FAO-PNUMA

1985, Kinler et a!. 1987). Paradoxically, most of the ecological and behavioural information on this species has been collected from feral or captive animals in North America and Europe, where coypus were intentionally or accidentally introduced (e.g. Hillbricht and Ryszkowski 1961, Gosling 1981, 1986, Doncaster and Micol 1989). In this paper, we report winter activity of free-ranging coypus inhabiting the Delta of Paraná River (eastern Argentina) as determined by radio- tracking. This region is considered the typical location of the species (Ximénez et a!. 1972).

In mammals, daily patterns of activity have been related to an endogenous activity rhythm (Aschoff 1966, Ashby 1972) and environmental determinants, particularly in rodents (Ashby 1972, Vickery and Bider 1981). Previous infor­ mation on coypu activity indicates that the coypu is mainly nocturnal (Lomnicki

F. Palomares et at.

1957, Chabreck 1962, Gosling 1979), with higher levels of locomotor activ around dusk and dawn (Chabreck 1962). Diurnal activity may occur during c winters (Gosling et at. 1980). However, this information has been obtained captive animals or feral populations of introduced individuals far away from I coypu natural range. Whether the patterns described in these studies are shai or not by coypus in their original habitats is not known because no compara data are available from natural South American coypu populations. We test I hypothesis of an endogenous nocturnal activity rhythm in this rodent and evalu. the effects of some environmental determinants on coypu activity.

Study area and methods
The study area was a natural freshwater marsh situated 5 km east of Puerto Constanza (Delt the Parand River, Entre Rios, Argentina; 34’S, 58—60’W). Water depth was 50—90 cm. Emerl vegetation in the marsh was mainly by giant bulrush Scirpus sp., which was distributed in patc of variable density, sometimes accompanied by arrowhead Sagittaria sp., water hyacinth Posited’ sp. and Eichrornia sp. Snbmergent vegetation included water fern and milfoil (Myriophyflum Salvinia sp. and Hidrocotile sp.), as well as Alternanthera sp. The area is managed for grazin cattle; revenue from wildlife, particularly coypus, is also important in he study area. The climat characterized by mild winters and hot summers (mean annual temperature = 17’C); annual raft is about 1100 sam.

Each of six coypus (3 subadult males; 1 young, 1 subadult and 1 adult females) were tracked seven 24-h periods in August 1990. Age and reproductive condition was estimated from body a (Crespo 1974). Coypus were equipped with radiocollars that inorporated motion sensors (Biotr: Wareham, U.K.). The signal was received by a portable La-12 receiver (AVM, Livermore, Califor via a 3-element Yagi antenna. During each 24-h period of radiotracking, the activity of each ani was checked every hour, and its position determined by triangulation every 2-h. Activity inactivity were distinguished after one minute listening to tip switches of the radiocollar mo sensor (Knowlton et al. 1968). Animals were considered active when the radio signal india movement. Coypu positions were determined at distances observer-animal ranging from 50 to 30( Activity patterns were described using the percentage of bearings with activity for each ha interval, and by determining the mean of the shortest distance travelled in each 2-h interval. total percentage of bearings with activity (an estimate of the daily time spent active) and minimum distance travelled per 24-h period were also estimated.

For each hourly record of activity, 6 environmental variables were measured: air temperature

wind conditions (6 categories following Beanfort scale; Peterson 1968), cloud cover (4 categos

0—25%, 25—50%, 50—75%, and 75—100%), and presence or absence of visible moon, fog, and r respectively. Day was subdivided into 8 periods: twilight (07.00—08.00 h and 18.00—10.00 h), dayt (09.00—17.00 h), and nightime (20.00—06.00 h). Moon was only scored at night and cloud cover diii daylight.

Individual differences in activity patterns (analyzed only from percentage of bearings activity; see Pnlomares and Delibes 1991) were tested by Spearman rank correlation coefficient Differences in daily activity time and distance travelled were tested nsing the Kruskall-Wallis (H). The dependence of activity on environmental variables was examined using an unsaturs linear model based on logistic regression and maximum likelihood estimation (procedure CATMOI

SAS; SAS 1988). The response variable (activity) was considered to have just two levels (activi

inactive), and the independent variables included both qualitative (wind speed, cloud cover, moon, rain, and time of day) and quantitative (temperature) factors. To account for possible nonlit

Winter activity of coypus in Argentina 85

responses of activity to temperature, the square of this variable was added to the other independent variables. The effect of environmental factors on the rate of movement was analyzed using a general linear model (procedure OhM; SAS 1988). Distances were log-transformed for the analysis. As distance travelled was estimated from each 2-h interval and S records of each environmental thctors were obtained for each one of them, we considered the intermediate value for the model.

Coypu activity was mainly nocturnal, with two activity peaks: one around

20.00—21.00 h, approximately one hour after sunset, and the other between 04.00 and 06.00 h, approximately two hours before sunrise (Fig. 1). Daily activity patterns were similar among all individuals (all r5 > 0.50, allp <0.015). The meaii proportion of daily bearings with activity was 54.2% (n = 42, SD = 11.5, range =

29.2—79.2). Although some individual variation was observed (individual means ranged from 47.9 to 63.0%), it was not statistically significant (H = 10.86, p =


Two environmental factors were

found significantly related to coypu ac­

tivity: period of day and rainfall (Table

1). Coypus were active on 78.8% of all bearings made during the night (n =

444), compared to only 22.6% during daylight (n = 376), Intermediate val­ ues were obtained for twilight (57.8%,

)-_ 120




n = 166). On the other hand, coypus

were more active during rain (58.3%,

n = 24) than without it (53.3%, n =

980). Removing twilight periods from the analyses to prevent the possible


+ TIME +

I2,D2 i:iiiiiiiliiij

influence of a period of transition in coypu activity, resulted in similar find­ ings (Table 1). A separated analysis of the influence of environmental factors on coypu activity during the night and the day, revealed that rain only affect­ ed it to some extent during daylight, and no factors at nighttime (Table 1).

Coypu locomotor activity was also higher at night than during daylight



J 150

12-14 10-10 20-22 24—2 4-0 0-10


(Fig. 1). Mean distance travelled peaked between 02.00 and 04.00 h (Fig. 1).

Mean minimum daily distance travell­

ed was 1.25 km (ii = 42, SD = 0.60,

Fig. 1. Winter activity patterns of radiotracked free-ranging coypus in tbe Farand River Delta (Argentina) as estimated by percentage of bear­ ings with activity and rate of movements. Arrows show sunset and sunrise during the study.

F. Palomares at at.

Table 1. Influence of environmental factors on coypu activity. 2) Temperature x temperature, a

factor was not scored for some of the day periods included in the analysis, b the factor was not sc for this period, c the factor was not present during this period.
Independent General snslysis Daylight and night only Daylight Night



2 . 2























































Day period





























Table 2. The lack of influence of some environmental factors on nocturnal 2-hour movements of coypus

(from 20.00 to 06.00). 2) Temperature x temperature.

Independent df Fvalue p variable
Temperature 1 2.86 0.093

Temperature21 1 2.93 0.089

Moon 1 0.01 0.913

Fog 1 0.12 0.726

Wind 3 1.39 0.247

range = 0.41—2.59). Individual mean minimum daily distances ranged from C

to 2.00 1cm, but the differences were not statistically significant (H = 9.78,


We only analyzed the influence of environmental factors on coypus Iocomt activity during night. No environmental factor was significantly related to co:

nocturnal movement rate (Table 2).


Winter activity of free-ranging coypu living in its natural environment is mai nocturnal. Onset of activity occurs shortly after sunset; high levels of locom activity are maintained during the night. These results agree with those repoi for captive and feral introduced coypus elsewhere (Lomnicki 1957, Chabreck II Gosling 1979). The activity pattern suggests that the end of activity is it variable (with the peak less pronounced) than the onset. Temperature did

Winter activity at coypus in Argentina H?

seem to influence coypu activity, as it had been previously observed by Gosling (1979). Chabreck (1962) also detected no changes in coypu activity due to temper­ ature. This difference may be a result of colder night temperatures in Britain where Gosling carried out his observations; the mild minimum air temperatures reached during our study (range: 9-45°C) did not seem to be critical to coypus. The only environmental factor that we detected influencing coypu activity was the occurrence of rainfall during the day. Movements to avoid adverse weather conditions could explain this result.

The two methods used in this study to assess the patterns of daily activity

coincide to reveal the nocturnal habits of this species; however, activity peaks were in different times with each method. This result may be explained in relation to the expected predominant behaviour that coypus exibited at those intervals. In captive animals, Gosling (1979) observed that feeding was more intense in the early evening, and that other activities such as nest building and autogrooming, increased around sunrise. Since these activities may be accomplished with short or without displacements, they would be detected only throughout recording activity as revealed by the motion sensor of the transmitters. On the other hand, captive coypus performed swimming activities with greater intensity after mid­ night (Gosling 1979), in coincidence with the observed peak in coypu movements in this study. Because coypus at the study area presented large home range overlapping (authors, unpub.), this behaviour could be. also related with their spatial erganization and nodal interactions which seem complex in this species (Ryszkowski 1966, Doncaster and Micol 1989).

It can be considered that only light conditions (period of the day) accounted for significant variation in the activity of coypus. The similarity between the circadian rhythms observed in our study area and those obtained in captive and feral coypus in areas where the species was introduced, suggest that the nocturnal pattern observed Teflects an endogenous activity pattern which has evolved in the nature range (Aschoff 1966, ]Jaan and Aschoff 1975, Gosling 1979).
Acknowledgements: The research was partially supported by the Spanish Ministerio de Educaciun y Cieneia and the Junta de Andalucia. A. Pulenta provided housing and logistic support during the fieldwork. we thank to 0. Maglione for trapping animals and for allowing us to carry out this study on his property. 8, Quintana and J. Merler helped with the fieldwork. C. M. Herrera performed part of the statistical analysis and made useful comments during the preparation of the manuscript. L. M. Gosling kindly reviewed an earlier version of the manuscript.


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Received .13 January 1993, accepted 2 November 1993.

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