When Ducklings Fight Over a Fish: Urban Spot-billed Ducks, Cooperative Parenting, and Everyday Wildlife Along a Japanese River

 One Fish, Many Stories: Daily Field Notes from an Urban Spot-billed Duck Family

A single fish became the center of an unexpected family drama.

During this day's observation, several ducklings competed intensely over a captured fish—only for the mother duck to end the contest in the most efficient way possible. Alongside this memorable moment, the family demonstrated confident descents over a river weir, careful foraging in shallow water, resting behavior, interactions with other waterbirds, and the continued exploration of a highly modified urban river.

This article documents one day's observations of wild Eastern Spot-billed Ducks (Anas zonorhyncha) living in an urban environment in Japan. Rather than presenting scientific conclusions, these notes are intended as careful field observations made by a long-term wildlife observer. Any behavioral interpretations should therefore be considered personal hypotheses based on repeated observations rather than established scientific fact.

For more than one thousand consecutive days, I have continued filming nearly every day while preserving the original recording dates. Most videos are published with minimal editing so that each upload also serves as a chronological record of what actually occurred on that specific day. When discussing behavioral patterns, I often compare them with observations from previous or subsequent days, treating these continuous daily records as supporting contextual evidence rather than isolated events.

Detailed explanations of the filming date codes and duck family identification codes used throughout these observations can be found here:

https://okasinaikimono.blogspot.com/p/welcome-to-wild-duck-diaries.html

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Field Observation Summary

The morning survey began with an unexpected reunion with family Pf2-42, which had not been observed for some time. Based on previous observations, I had expected this family to have moved downstream. Instead, they had apparently shifted farther upstream, suggesting another adjustment of their home range. At the same time, another nearby family (Sf9) could not be located despite extensive searching, raising further questions about changing territory use during this stage of duckling development.

At approximately 42 days of age, the ducklings of Pf2 negotiated river structures that would have been significant obstacles only a few weeks earlier. Their improved balance and climbing ability illustrated how rapidly young Spot-billed Ducks develop physical competence during the latter half of the brood-rearing period.

One duckling repeatedly investigated dense vegetation with unusual persistence. Although the exact motivation remains unknown, exploratory behavior toward vegetation appears occasionally during prolonged observations and may relate to hidden prey, curiosity, or environmental assessment.

Elsewhere along the river, another family of approximately 55-day-old ducklings rested together without their mother being immediately visible. It is relatively uncommon to find this particular family temporarily separated from the female. Based on comparisons with previous years, one possible explanation is that older broods begin exploring potential future resting or feeding areas while the mother forages nearby. However, this remains only a personal interpretation.

Another family (Ef5-19) later passed the resting brood while continuing steadily downstream. Their movements throughout recent weeks have been especially variable compared with many other families observed in the same river system.

One particularly entertaining moment occurred when a single duckling became completely absorbed by examining a vertical concrete wall while the rest of the family continued moving. Similar episodes have occurred repeatedly within this family, whose members often display unusually curious or playful-looking behavior during foraging and exploration.

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The Fish That Nobody Won

The most memorable event occurred when one duckling located a relatively large fish.

Almost immediately, siblings gathered and began attempting to steal the catch from one another. The fish appeared large enough that it may have been difficult for a young duckling to swallow efficiently. Before the contest could continue, however, the mother duck simply took possession of the fish herself, ending the dispute instantly.

Whether this represented parental intervention, opportunistic feeding, or simply the fastest solution is impossible to determine from observation alone. Nevertheless, the sequence offered an interesting glimpse into feeding competition within a duck family.

Spot-billed Ducks are generally considered omnivorous, feeding primarily on aquatic plants, seeds, insects, mollusks, crustaceans, and various small aquatic organisms. Fish are not necessarily their primary prey, yet I have documented multiple occasions on which both adults and ducklings captured small fish. Such observations suggest that fish may represent an opportunistic food source when available.

Later in the day, the same family was also observed actively hunting underwater prey in shallow water, possibly freshwater shrimp or other aquatic invertebrates. Their rapid pecking motions beneath the surface differed noticeably from their typical dabbling behavior and appeared relatively uncommon during my daily observations.

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Learning to Navigate Human-Made Rivers

One encouraging observation involved the ducklings confidently jumping from a low weir into the water.

Earlier in the breeding season, another family repeatedly avoided similar drops by taking longer detours through fish passages. Seeing these older ducklings descend directly suggests increasing confidence and physical capability as they mature.

The family later crossed the river, although one duckling briefly remained behind after hesitating near a fishway. Rather than panicking, it calmly searched for an alternate route before successfully rejoining the others. Such moments highlight the gradual development of independent decision-making while still remaining closely connected to the family.

Another particularly charming moment occurred when a duckling unexpectedly climbed onto the riverbank directly in front of the camera while preening, providing an unusually close view of its developing plumage.

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A River Shared by Many Species

Throughout the survey, numerous other bird species and wildlife also occupied the same urban habitat.

A juvenile Grey Wagtail demonstrated excellent camouflage while preening among riverside stones.

A Common Kingfisher was observed bathing before switching to prolonged feather maintenance.

Tree Sparrows also bathed enthusiastically in shallow water later in the afternoon.

Several other Spot-billed Duck families were encountered at different stages of development, illustrating how multiple broods simultaneously utilize different sections of the same river while apparently adjusting their spacing as ducklings mature.

White flowers of Gaura and blooming Tiger Lilies added seasonal context to the midsummer riverside landscape.

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Continuing Questions

Not every family expected during this survey could be located.

Several broods recorded on previous days—including Sf9, Ef6, Gf7, Xf5, Uf1, アf3, and Tf8—were absent despite targeted searching. Daily monitoring often reveals that duck families temporarily disappear before reappearing several days later in entirely different sections of the river.

Likewise, I had hoped to relocate an adopted duckling previously associated with family Df5. Although the mother was eventually found, the fostered duckling could not be confidently identified. As ducklings mature and juvenile plumage becomes increasingly similar, distinguishing individuals becomes progressively more difficult without continuous observation.

These unanswered questions are an important part of long-term field observation. Wildlife rarely follows predictable patterns, and documenting both successful and unsuccessful searches provides a more accurate record of what actually occurred.

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Species Recorded

• カルガモ

  Eastern Spot-billed Duck

  Anas zonorhyncha

  The primary study species. An adaptable duck commonly inhabiting urban rivers throughout East Asia.

• コサギ

  Little Egret

  Egretta garzetta

  A small white heron that frequently forages alongside ducks in shallow freshwater habitats.

• キセキレイ

  Grey Wagtail

  Motacilla cinerea

  A river-associated wagtail whose juveniles often rely on subtle plumage for camouflage.

• カワセミ

  Common Kingfisher

  Alcedo atthis

  A specialized fish-eating bird well known for rapid plunge-diving and frequent feather maintenance.

• スズメ

  Eurasian Tree Sparrow

  Passer montanus

  A familiar urban bird that regularly bathes in shallow water during warm weather.

• コイ

  Common Carp

  Cyprinus carpio

  Large omnivorous freshwater fish commonly inhabiting Japanese rivers and often sharing habitat with ducks.

• オニユリ

  Tiger Lily

  Lilium lancifolium

  A striking native summer flower frequently growing along moist riverbanks.

• ハクチョウソウ

  Gaura (Beeblossom)

  Oenothera lindheimeri

  An ornamental flowering plant often naturalized along riversides, blooming throughout summer.

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Every day in an urban river presents countless small events that could easily go unnoticed. Yet when these observations are documented continuously over months and years, even ordinary moments—such as siblings competing over a single fish or a duckling learning to descend a concrete weir—become valuable pieces of a much larger story.

This ongoing record is not intended to provide definitive scientific conclusions, but rather to preserve the chronology of everyday wildlife behavior as faithfully as possible. Over time, these accumulated observations may offer useful context for understanding how wild Spot-billed Ducks adapt, raise young, and survive within highly modified urban environments.