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Ecological Intelligence

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Ecological Intelligence / Subject

seasonality

Peer-reviewed North America

City bird-diversity gradients change with season and latitude

Evidence
Peer-reviewed
Geography
Roughly 452 North American cities and surrounding landscapes
System
Cities as habitats; bird richness; urban seasonality

WHAT THE EVIDENCE SAYS

Researchers analyzed approximately 17 million eBird observations spanning hundreds of North American cities. Winter native bird-richness gradients across latitude differed between urban and nearby nonurban landscapes; introduced birds showed weaker latitude effects, and some urban relationships changed direction under colder conditions.

WHY IT MATTERS / OUR READ

Treat a city as a seasonally shifting ecological landscape rather than a single point on a greener-is-better scale. Migratory dynamics, nonnative assemblages, heat, feeders and neighborhood vegetation can each alter what a city survey actually detects.

CAVEATS / UNCERTAINTY

eBird is opportunistically sampled, so participation and effort bias remain important. Associations do not prove urban refuges are improving population survival or that all cities share the same pattern; model and reporting choices influence city comparisons.

SOURCE

Nature Cities · North American city bird-diversity analysis
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A 17-million-record North American citizen-science analysis shows why an urban wildlife signal depends on winter, latitude and the mix of native and introduced birds.

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Six thousand recorder-days reveal overlapping but different whale seasons in the Mascarene waters

Evidence
Peer-reviewed passive-acoustic monitoring study
Geography
Mascarene waters, southwestern Indian Ocean
System
Open-ocean marine mammal habitat

WHAT THE EVIDENCE SAYS

Sixteen ocean-bottom recorders provided more than 6,000 days of recordings. Fin-whale 20-Hz songs occurred on an average 43% of recording days and could span up to roughly eight months at a site. Antarctic blue-whale songs were detected at all sites but on about 13% of recording days on average, concentrated mainly outside austral spring–summer, with geographic exceptions. Madagascar pygmy blue whales also showed strong seasonal occurrence.

WHY IT MATTERS / OUR READ

Sparse visual sightings can make a marine corridor look empty. Long-duration passive acoustics reveals when different large whales overlap the same broad seascape and can help time surveys, shipping-risk assessment or other monitoring around actual seasonal presence.

CAVEATS / UNCERTAINTY

Acoustic presence is not abundance, and calling behavior varies by species, sex, season and context. Recorder placement and detectability also shape apparent occurrence, so silence cannot be treated as confirmed absence.

SOURCE

ICES Journal of Marine Science — primary study
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Passive acoustics found fin, Antarctic blue and Madagascar pygmy blue whale songs across all sampled sites, with strong seasonality and much sparser Antarctic-blue occurrence.

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Peer-reviewed Africa

In Kakamega Forest, the season changed the butterfly community more than the habitat label did

Evidence
Peer-reviewed
Geography
Kakamega Forest ecosystem, Kenya
System
Tropical rainforest fragment / butterfly community

WHAT THE EVIDENCE SAYS

Weekly surveys from January through June 2024 recorded 10,334 butterflies representing 146 species across six cover types. Abundance, richness and Shannon diversity rose in the wet season, community composition separated by season, and one-month-lagged rainfall was the strongest abundance predictor. Natural and secondary forest still supported the highest abundance and diversity, but season explained more overall community variation than habitat type.

WHY IT MATTERS / OUR READ

Biodiversity monitoring can misread habitat differences when sampling windows do not span seasonal transitions. For tropical insects especially, timing is part of the survey design—not background noise.

CAVEATS / UNCERTAINTY

This is one six-month study in one rainforest fragment. It does not establish a long-term climate trend, and seasonal dominance in this system should not be generalized to other taxa, years or tropical forests.

SOURCE

Journal of Tropical Ecology
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Six months of weekly surveys across six forest-cover types found wet–dry transitions explaining more community variation than habitat type, with lagged rainfall the strongest abundance predictor.

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