Address: Øymælen 440, 7224 Melhus
Coordinates: 63.341°N, 10.215°E
Municipality: Melhus, Trøndelag, Norway
Habitat: Wetland nature reserve - marshes, shallow water, reedbeds
Significance: Stopover site along East Atlantic Flyway used by migrating waterfowl during study period
Recording Period: October 13-15, 2025 (48.8 hours)
Temperature: 7-11°C (44-52°F)
Conditions: Heavy rain and fog throughout recording period (80%+ of time)
Wind: Light to moderate
Visibility: Low due to fog
Impact on Data: Rain noise contamination in all recordings - required extensive audio enhancement (Wiener filtering + HPSS)
IMPORTANT: 80%+ of recording occurred during rain/fog conditions
Cannot claim: Species correlations with specific weather conditions
Can claim: These species are detectable during poor weather / Species present during autumn migration period
Great Bittern lesson: 129 false positives from rain drops hitting microphone - demonstrates challenges of wet-weather acoustic monitoring
87% of all detections came from social/flock species, revealing a highly gregarious avian community.
Graylag Goose: 59 flock events detected, 98.7% of calls occurred in flocks
Largest flock event: 620 calls over 91 minutes
Vocal intensity: 58.8 calls per hour
8,778 geese-crow co-occurrences - pattern consistent with sentinel mutualism hypothesis
Hypothesis: Crows may act as early-warning sentinels, potentially benefiting geese with enhanced predator detection
Evidence: Pattern resembles heterospecific eavesdropping documented in literature (Magrath et al. 2015, King & Rappole 2023)
Limitation: Acoustic co-occurrence alone cannot prove functional benefit - behavioral observations needed
37 migratory species detected (45% of verified species)
Nocturnal flight calls: 47 calls between 01:00-06:00 (peak 03:00-04:00)
Species: Pink-footed Goose, Common Crane, Greater White-fronted Goose
Significance: Documents active migration along established flyway routes
189 detections, 61% during crepuscular periods
Peak timing: 20:00-21:00 (82 calls at 20:00)
Interpretation: Dusk calling during autumn migration to Africa (October = migration season, not breeding)
Conservation: Declining species across Europe - stopover site documentation important for migration monitoring
Detection counts: Only best example per species manually verified, not all 4,023 detections
Weather bias: 80%+ recording during rain/fog - cannot make weather correlation claims
Rare species: Species with <10 detections have limited validation
Sampling period: Single location, single season (autumn migration)
BirdNET v2.4 Built-In Filtering:
Praven Pro 2.2 Biological Validation (This Study):
Key Distinction: BirdNET filters reduce the species list based on geography/season. Praven Pro validates detected species against behavioral ecology after BirdNET analysis. Both are complementary and necessary.
Detections: 2,871 (69.9% of all verified detections)
Behavior: Pronounced flock calling - 98.7% of calls in flocks
Vocal intensity: 58.8 calls/hour
Largest event: 620 calls over 91 minutes (16:00-17:26, Oct 13)
Significance: Dominates wetland soundscape, classic sentinel-nuclear species in mixed flocks
Detections: 189
Behavior: Dusk calling during autumn migration (61% crepuscular)
Peak activity: 20:00-21:00 (82 calls at 20:00)
Interpretation: Migration stopover calls (October = migration to Africa, not breeding season)
Conservation: Declining across Europe - stopover site monitoring valuable for population assessment
Original detections: 59 (now rejected)
Reason for rejection: Spectrogram analysis revealed rain noise misclassified by BirdNET
Seasonal implausibility: Species should have migrated to Africa by mid-September (October presence extremely unlikely)
Evidence: All 3 spectrograms showed broadband noise characteristic of rain, not bird vocalizations
See: GRASSHOPPER_WARBLER_REJECTION.md for detailed analysis