The ranging patterns of female bottlenose dolphins with respect to reproductive status: Testing the concept of nursery areas

• We compared the ranges of female bottlenose dolphins when with calf vs. without calf.
• We conducted longitudinal (paired) and cross-sectional (unpaired) analyses.
• Variation among individual females was greater than by reproductive state.
• Home ranges were not larger when females were with nursing calves.
• Females concentrated in different areas depending on their reproductive status.

Adult female bottlenose dolphins (Tursiops truncatus) form fission–fusion social networks and adjust their association patterns with respect to their reproductive status. It is commonly reported that mothers with dependent calves preferentially utilize ‘nursery areas’ consisting of protected, shallow water habitats. However, few studies have tested whether females adjust their ranging patterns based on their reproductive status. Using photo-identification data from the Indian River Lagoon, Florida (1997–2007), we conducted both longitudinal and cross-sectional analyses to compare the ranging patterns of adult females with calves versus females without calves. The size of females' home ranges (HR) and core areas (CA) were not significantly different between reproductive states (P > 0.05), presumably due to a lack of directional pattern in the relative sizes of female's home ranges when with a calf and without a calf. HR size varied greatly among individual females, 9.37–190.83 km2 for females with a calf (x¯ ± SE = 76.50 ± 10.20 km2) versus 20.90–186.13 km2 for the same females without a calf (97.00 ± 11.50 km2). CA size ranged from 0.35 to 56.75 km2 for females with calves (14.62 ± 3.60 km2) and 0.39 to 49.72 km2 for females without calves (20.01 ± 3.60 km2). Overlap between females' ranges with calf and without calf also varied greatly among individuals (HR: 13.92–94.97%, CA: 0–93.97%). On average, females with calves continued to utilize 51.98 ± 5.08% of their without calf HR but only 19.09 ± 5.45% of their without calf CA. In our cross-sectional analyses, a large percentage (65.55 ± 3.36%) of the 95% utilization distribution for females without calves was also used by females with calves across all seasons. However, overlap between the 50% utilization distributions of females with calves and females without calves was low (< 11%) in all seasons, especially autumn. These findings suggest that variation in ranging patterns among individual females was greater than by reproductive state. Females continued to use a large proportion of their overall range, but concentrated in different areas depending on their reproductive status.