Observations.

Interactions between adult bottlenose dolphins and manatee calves were collected during dedicated boat-based marine mammal surveys from 2001 to 2017 for studies of dolphins and manatees in Belize [36–41]. This included opportunistic observations of at least one member of each species interacting, confirmed by marine mammal experts in the field during dedicated boat-based surveys. Animals were primarily observed from land and from small motorboats (6–8 m long) equipped with outboard engines. For boat-based sightings, observers collected photo-identification photos using DSLR cameras with telephoto lenses (100–400 mm) and sampled the surface behavior of dolphin groups ad libitum [42]. Dolphin behavior states were defined as follows based on the literature [43, 44]: Traveling: persistent directional swimming; Socializing: interaction of two or more individuals of either species within one body length of each other, often involving social displays, chasing, and body contact with other individuals; Foraging: repeated diving and/or fast chases in pursuit of prey; and, Milling: nondirectional movements. Other behaviors including all affiliative (swimming alongside the calf) and agonistic behaviors (e.g., attempts to submerge the animal, hit it, or launch it into the air) were described where possible.

Two cases were filmed with two small aerial drones: a DJI Phantom 4 Pro (2016) and a DJI Mavic Pro (2020), filming in 4K (3840 × 2160 dpi) at 30 fps. Drones were operated at altitudes of 20 to 150 m by EAR and JG using a remote control while piloting from the shore or from a small boat. The video feed from the onboard camera of the drone was streamed live to an iPad (Apple, Inc.) to monitor animal activity and adjust speed and trajectory of the drone. Observations continued until animals went out of sight, if they moved out of the range of the drone’s flight capacities, and/or until the batteries died. Video footage was stored to a microSD card and was later reviewed in QuickTime Player 7 (Apple Inc.) to describe observed behaviors. In the two cases detected by drone, footage was reviewed to identify behavioral events using continuous all-event sampling [42]. To estimate distances between animals in aerial footage, we used the approximate size of adult bottlenose dolphin as measured from scaled drone footage of an adult coastal bottlenose dolphin (250 cm body length: [45]).

Additionally, videos and images captured by citizen scientists with cell phone cameras were reviewed to identify behaviors in attempts to describe interspecies interactions.

Examination of orphaned calves.

Evidence of interactions initiated by bottlenose dolphins towards Antillean manatee calves were collected during health assessments of orphaned individuals found by the Belize Marine Mammal Stranding Network (BMMSN). Calf health was evaluated upon intake to Wildtracks in Sarteneja, Belize, the primary rescue and rehabilitation center that raises and releases injured and orphaned manatees. Observations of solitary and potentially orphaned calves were first reported to the BMMSN. In the event a calf was deemed in need of rescue (i.e., alone, small size without mother, visibly injured or ill), it was captured and transported to Wildtracks. Physical capture and handling of manatees for rescue was permitted by the Belize Forest Department and Belize Fisheries Department to JG, ZW, and PW. Upon entry to the rehabilitation center, live calves underwent an initial health assessment and calves that did not survive were necropsied. During examinations, bodies were externally inspected for the presence of anomalous scarring, photographed, and body size was measured with a soft ruler tape according to standard protocols [35].

Calves were animals < 175 cm in total body length [46]. Wounds on the calves were identified as tooth rakes by the presence of clusters of evenly spaced and thin parallel rakes [25]. To confirm their origin, we measured the distances between tooth rakes in photos of manatee wounds and compared these values to previously reported inter-tooth distances of bottlenose dolphins: 5–14 mm [28]; 7–12 mm [18]; and 10.97–12.32 mm [21]. The distances between tooth rakes were measured in Image J by tracing a line between two points in adjacent pairs of parallel tooth rakes.

Case 1.

On 9 August 1999, a marine mammal researcher sighted a group of three to five bottlenose dolphins interacting with a young manatee calf from a small motorboat (B. Bilgre, pers. comm., 20 June 2014). The group was first sighted at 11:14 near a channel opening to the Drowned Cayes near the Belize Barrier Reef (Fig 1). The group split into smaller sub-groups, remaining within 30 m of each other for the remainder of the sighting. At 11:41, a manatee calf (probably neonate) was detected and was quickly surrounded by a group of five bottlenose dolphins, including four adults and a juvenile individual. For 15 min, the dolphins exhibited a variety of social and affiliative behaviors directed at the manatee calf including rubbing and supportive behaviors, with the dolphins appearing to push the manatee calf to the surface.

On the same day at 14:00, a single adult bottlenose dolphin and a manatee calf were sighted 5 km east of the previous sighting (Fig 1). The boat followed them as they swam together through a channel between Swallow Caye and Stake Bank Caye and across shallow water seagrass habitats in the Drowned Cayes for 63 min (N. Auil Gomez, pers. comm., 20 June 2014). The dolphin was observed swimming with the manatee calf and displayed affiliative behaviors towards it. The calf first appeared to mill and stayed beneath the peduncle of the dolphin. The dolphin was also seen exposing its ventral surface toward the calf. The observation ended as the pair moved southward into deeper waters at 15:03. Neither animal was re-sighted. Both events most likely involved the same calf based on the short distance between locations and short time between detections.

Case 2.

On 10 June 2015, an adult bottlenose dolphin was observed from shore by a resident, later assisted by personnel from BMMSN, near a dock immediately south of the Belize River in the Driftwood Bay area in Belize City (Fig 1; R. Codd, pers. comm., 11 July 2014). A manatee calf was observed actively swimming in echelon position alongside the dolphin. The dolphin was observed investigating the calf with its rostrum (Fig 3; See S1 Video). Large splashes and vigorous subsurface movements suggested the dolphin was also harassing the calf. In four short clips totaling 91 sec, dolphin harassment and echelon swimming were observed alternatively.

Case 3.

At 15:34 on 30 June 2016, a mother-calf bottlenose dolphin pair was observed by EAR interacting with a mother-calf manatee pair in aerial footage captured with a DJI Phantom 4 Pro. The interaction occurred 200 m east of the leeward side of St. George’s Caye (Fig 1; see S2 Video). The calf was large (>170 cm body length), suggesting it was more than a year old. The dolphin pair traveled slowly over seagrass meadows heading northwest as they passed within ∼30 m of a manatee mother-calf pair. As the dolphins passed, the female manatee began to submerge, followed by the calf. The female dolphin and her calf abruptly changed direction swimming directly towards the manatees until within 5–8 m (Fig 4). The dolphin mother-calf pair turned away again and then rapidly approached the manatees. Upon surfacing, both dolphins swam directly towards the manatees, swimming within 1 m of them and possibly making contact. However, water turbidity prevented making further observations. The two manatees remained relatively stationary. After swimming near them, the dolphins turned away and left the area. The entire interaction lasted ∼50 sec, from the moment the dolphins oriented towards the manatees until the dolphins left the area.

Case 4.

At 10:00 on 27 June 2018, four bottlenose dolphins were observed for approximately 60 min as they interacted with a group of manatees near Long Caye (Fig 1) (D. Smith, pers. comm., 20 July 2018). At the beginning of the sighting, the dolphins swam near a manatee calf and its presumed mother. Several dolphins in the group appeared to harass the mother and attempted to separate the calf from the adult by swimming between the pair and lifting the calf while swimming away. A single adult dolphin continued to swim alongside the calf the manatee calf near the edge of the mangrove caye for several minutes. The calf swam near the dolphin for several minutes, briefly filmed with an Apple iPhone 6 (Fig 3; see S1 Video). The calf swam on the dolphin’s side in echelon position and underneath the peduncle of the dolphin as they both traveled in shallow waters. Several minutes later, a single dolphin was observed displaying aggression and attacking the calf, ramming the calf out of the water into the mangroves and repeatedly biting it. The calf was manually retrieved from the water by JG and transported to the Belize City and then on to Wildtracks for care and rehabilitation.

Case 5.

On 02 April 2020, a group of manatees (n = 11) and a group of foraging bottlenose dolphins (n > 4) were filmed by JG using a DJI Mavic Pro on a shallow seagrass bed in the Drowned Cayes (Fig 4; see S2 Video). A mother-calf calf manatee pair entered the area and began feeding, quickly followed by a single dolphin that repeatedly approached the manatee pair. In 4 min and 13 sec of drone video, the dolphin swam in counterclockwise circular paths around the pair 11 times. The two manatees made numerous attempts to depart the area, but the dolphin repeatedly cut off their path (Fig 4). The ability to observe the interaction was interrupted at 30 minutes as the drone had no charged batteries available.

Case 6.

At ∼16:00 on 5 July 2020, a bottlenose dolphin was seen interacting with a manatee calf in Haulover Creek in Belize City (J. Williams, pers. comm., 6 July 2020). The dolphin repeatedly surfaced near the manatee and appeared to swim over the manatee’s nares when the calf came up to the surface for a breath (Fig 1). The calf repeatedly surfaced swimming alongside the dolphin in echelon position. The interaction lasted for approximately 20 min before both animals were lost from sight.

Case 7.

At 13:48 on 19 July 2020, a resident of the Bella Vista area sighted a solitary manatee calf (< 150 cm) swimming rapidly behind and on the right side of an adult bottlenose dolphin in a narrow canal (Fig 1; Z. Reich, pers. comm., 21 July 2020). In an 18 sec video of the animals (see S1 Video), the calf remained in close proximity with the dolphin. Extensive searches of the canal and the adjoining canals via boat, drone, and on foot were unsuccessful for resighting both animals. On 24 July 2020, a dead calf was reported in advanced decomposition in a canal approximately 120 m from the location where the dolphin was seen with the calf, but it could not be confirmed if they were the same calf.

Case 4 (bite mark examination).

The calf (ID: MRP22) observed in the wild in Case 4, entered the rehabilitation facility weighing 20.3 kg with a total body length of 108 cm and was identified as a male. A section of the umbilical cord was still attached to the calf indicating it was a newborn. There were several clusters of tooth rakes on its right side and on the tip of its right pectoral fin, the distal end of its flukes, and oriented both parallel and perpendicular to each other likely representing several separate bites (Fig 2). Some tooth rakes were deep enough to be of concern for causing infection. The calf died 13 days later but it could not be determined if the cause of death was associated with the interaction with dolphins or another cause.

Case 8.

On 25 June 2009, a manatee calf (ID: MRP08) was observed from shore swimming alone in a depression north of Heusner Caye by the local caretaker of the caye (Fig 1; M. Lambey, pers. comm., 25 June 2009). The calf was observed for several hours to see if it would reunite with its mother or if it would need to be rescued. Several hours later it was still alone, and a rescue operation was organized by BMMSN. A gillnet was used to capture the calf. It was transported by small boat to Belize City and then transferred to Wildtracks.

Upon entry to the rehabilitation facility, the young female calf weighed 25.4 kg with a total body length of 118 cm. Health assessment revealed signs of dehydration and emaciation. Multiple deep skin lacerations were found on the head, right pectoral fin and tail that consisted of clusters of long, thin parallel lines consistent with bottlenose dolphin tooth rakes (Fig 2). The calf fully recovered from these wounds and was raised and rehabilitated at Wildtracks until her successful reintroduction in 2012.

Case 9.

In the morning of 15 August 2019, a local tour guide and fisherman found a lone manatee calf (ID: MRP24) in Haulover Creek near Belize Mills in Belize City (Fig 1) and reported it to the BMMSN. The animal was exhibiting difficulties to surface and breathe. The 93 cm-long female calf was retrieved but died before it could be transported for rehabilitation. The body was covered in brown algae and presented various circular wounds on the head and throughout the rest of the body. There were a series of tooth rakes at the anterior tip of the right pectoral fin consistent with the bites of an adult bottlenose dolphin (Fig 2). The necropsy revealed the calf was severely emaciated and dehydrated as indicated by the hard and dry fecal matter found in the large intestine. The yellow coloration in the lumen of the stomach was indicative of a lack of recent feeding and suggests the calf had either been unable to eat or was separated from the mother for days. The cause of death is unknown.

Case 10.

On 13 July 2020, a manatee calf was found swimming alone near Vista del Mar along the coast of Belize City (Fig 1). The calf (105 cm body length) was reported to the BMMSN, and it was successfully located and transported to Wildtracks for rehabilitation. Photographs of the calf (ID: MRP26) taken upon entry to Wildtracks revealed several clusters of lacerations (Fig 2) consistent with bottlenose dolphin tooth rakes. One day following rescue, several additional clusters of bite marks were detected on the abdomen. The calf had two distinct clusters of tooth rakes, one on the tip of each pectoral fin. The manatee recovered and was moved to subsequent stages of release in June 2021.