Monitoring abundance and population trends of small odontocetes is notoriously difficult and labor intensive. There is a need to develop alternative methods to the traditional visual line transect surveys, especially for low density areas. Here, the prospect of obtaining robust density estimates for porpoises by passive acoustic monitoring (PAM) is demonstrated by combining rigorous application of methods adapted from distance sampling to PAM. Acoustic dataloggers (T-PODs) were deployed in an area where harbor porpoises concurrently were tracked visually. Probability of detection was estimated in a mark-recapture approach, where a visual sighting constituted a "mark" and a simultaneous acoustic detection a "recapture." As a distance could be assigned to each visual observation, a detection function was estimated. Effective detection radius of T-PODs ranged from 22 to 104 m depending on T-POD type, T-POD sensitivity, train classification settings, and snapshot duration. The T-POD density estimates corresponded to the visual densities derived concurrently for the same period. With more dataloggers, located according to a systematic design, density estimates would be obtainable for a larger area. This provides a method suitable for monitoring in areas with densities too low for visual surveys to be practically feasible, e.g., the endangered harbor porpoise population in the Baltic.

The aim of this study was to investigate the effects of social contact and milk allowance on social behavior, play behavior, and responses to handling in dairy calves. Forty test calves and 16 companion calves were allocated to 1 of 5 treatments from birth to 4 wk of age: (1) housed singly and fed 5 L of milk/d; (2) housed singly and fed 9 L of milk/d; (3) housed in pairs and fed 5 L of milk/d; (4) housed in pairs and fed 9 L of milk/d; or (5) kept with the dam and fed 9 L of milk/d. From 4 to 6 wk of age, all calves were offered 5 L of milk/d to promote intake of solid feed before weaning. At 6 wk of age, all calves were weaned, and at 7 wk of age, they were grouped (7 calves/group: 1 test calf from each treatment and 2 companion calves). The response to restraint during blood sampling was recorded weekly; singly housed calves struggled more during restraint than did calves kept with the dam, and pair-housed calves struggled at an intermediate level. Play behavior was recorded for 20 min/wk after the provision of fresh straw; calves housed singly and fed a low milk allowance spent less time playing than did calves in all other treatments. Three days after grouping, calves were subjected to a feed competition test; calves receiving the high milk allowance and housed in pairs spent more time feeding than did those receiving the high milk allowance and housed singly, with all other treatments showing intermediate responses. These results indicate that social contact decreased responses to restraint and increased play and competitive success. The high milk allowance increased play but reduced competitive success after grouping. Lower responses to restraint indicated less responsiveness to stress. Play is considered an indicator of positive welfare, and competitive success helps calves succeed in a group environment.

To investigate the effects of social housing and milk feeding on play behavior and performance, 48 Holstein-Friesian male and female calves were either individually or pair housed in straw-bedded pens (3.0 m × 4.5 m). Half of the calves in each housing treatment were fed a standard milk allowance (5 L/d from d 3 to 42); the other calves were fed an enhanced milk allowance (9 L/d from d 3 to 28 and 5 L/d from d 29 to 42). All calves were abruptly weaned on d 43. Play behavior was recorded for 48 h beginning on d 15, 29, and 43. Variables were square root-transformed before analysis, but back-transformed values are given. On d 15 the duration of locomotor play behavior was greater among enhanced- than standard-fed calves [15.2 vs. 10.8 (± 1.0) corresponding to 231 vs. 117 s/24 h]; this behavior decreased when milk allowance in the enhanced treatment was reduced on d 29. Across ages, the duration of locomotor play behavior was greater among individually housed than pair-housed calves [10.9 vs. 8.2 (± 0.6) corresponding to 119 vs. 67 s/24 h], but the total duration of play did not differ between individual and pair-housed calves [130 (45-295) s/24 h; median and interquartile range]. Only pair-housed calves could perform social play behavior (play fighting), and the duration of this was greater on d 15 and 29 than on d 43 [8.3, 10.7 and 3.5 (± 1.3) corresponding to 69, 115 and 12 s/24 h for d 15, 29, and 43]. Among calves on enhanced milk, pair-housed animals had a greater concentrate intake than individually housed calves (840 vs. 530 ± 110 g/d); for calves on standard milk, we detected no effect of housing [990 and 1,090 (± 110) g/d]. Among calves on enhanced milk, pair-housed calves had greater body weight gain than individually housed calves [990 vs. 850 (± 40) g/d]. For calves on standard milk, we observed no effect of pair versus individual housing [810 and 840 (± 40) g/d]. In conclusion, greater durations of play behavior in enhanced-fed calves suggest an animal welfare benefit of this feeding method. Enhanced-fed calves consumed less concentrate, but pair housing stimulated concentrate intake in these calves, suggesting that pair housing and enhanced feeding should be used together.

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This study compared the effect of individual and pair housing and age at pair housing on the social behavior of young dairy calves. Twenty-seven pairs of calves were reared from birth until 6 wk either individually (limited social contact between bars; L calves), in pairs (full social contact; F calves), or individually for 3 wk and in pairs for the next 3 wk (LF calves). From 6 to 7 wk of age, the calves were housed in a group of 6 calves (each group consisted of 3 pair of calves, 1 pair from each treatment). Video recordings of undisturbed behavior were obtained from each pair on d 2, 12, 22, and 34 (age of the youngest calf in a pair) and from the group pens on d 44 and 49 (age of the youngest calf in the group). Behavioral recordings were performed using instantaneous recording at 5-min intervals on d 2, 22, and 34 over 16 h to investigate overall activity and social activity of the pairs. Six of 6 F calves and 2 of 6L calves were sniffing and licking another calf on d 2. Calves from treatments F and LF were sniffing and licking another calf more on d 22 compared with on d 34, but we observed no difference between treatments F and LF. On both days, the F calves and LF calves were sniffing and licking another calf more than were the L calves. No difference was found in duration of lying down in body contact with another calf between F and LF calves on d 22; however, on d 34, LF calves performed more of this behavior than did F calves. Continuous recordings of social behavior were conducted for 3h on d 12 and 34. On d 12, we found no difference between F and L calves in the total duration of being actively engaged in social behaviors. On d 34, F and LF calves were more actively engaged in social behaviors than were the L calves. After grouping, lying behavior and nearest neighbor during rest were recorded instantaneously at 15-min intervals for 16 h on d 44 and 49. From d 44 to 49, the duration of resting increased, the duration of resting with a neighbor increased, and the duration of resting with the previous companion decreased. No difference was found between treatments after grouping in duration of rest and rest with a neighbor. In conclusion, from the age of 3 wk of life, calves housed with full social contact performed more social behaviors than calves housed individually with limited social contact, whereas only minor differences were found in the social behavior of calves housed together from birth compared with those housed together from 3 wk of life.