This interpretation is consistent with the observed timing and scale of reproductive loss in 2025. Following egg laying in May\u2013June, males incubate eggs through June\u2013July while females undertake extended foraging trips at sea (Fig.\u00a01a<\/a>). Given the timing of iceberg grounding in late July, incubation and hatching likely proceeded largely as normal. However, when females returned to relieve incubating males, iceberg-induced access constraints may have delayed or disrupted parental changeover. Likewise, males completing incubation may have experienced difficulty accessing viable routes to the sea, potentially compounding delays in coordinated foraging and return exchanges. Disruption of parental coordination during early chick rearing could reduce food delivery to newly hatched chicks, thereby increasing the risk of starvation20<\/a>,38<\/a>,39<\/a>. During the initial field survey in November 2025, multiple chick carcasses were observed within the colony area (Supplementary Fig.\u00a05<\/a>), consistent with elevated early-stage mortality.<\/p>\n Iceberg morphology and access constraints<\/p>\n Beyond the mere presence of a grounded iceberg, its particular morphology appears to have influenced the degree to which access to the Coulman Island breeding site was constrained. Photogrammetry-based elevation analysis (see Methods) reveals marked asymmetry in iceberg geometry along its grounding axis (Fig.\u00a04<\/a>). In the western sector (transects T1\u2013T2), the ocean-facing side forms a relatively gentle slope, whereas the colony-facing southern margin rises abruptly as a sub-vertical escarpment exceeding 20\u2009m in height, effectively limiting direct access to the breeding site. In the eastern sector (transects T3\u2013T4), steep ice faces are present on both the colony-facing southern side and the ocean-facing northern side, forming a more topographically confined configuration.<\/p>\n Fig. 4: Three-dimensional morphology and elevation profiles of the grounded iceberg at Coulman Island. a Regional topography derived from the Reference Elevation Model of Antarctica (REMA), overlaid with a high-resolution photogrammetric surface model of the grounded iceberg generated from aerial imagery (see Methods). The inset shows the iceberg surface colored by elevation, with the locations of four transects (T1\u2013T4) used for profile extraction. b Elevation profiles along transects T1\u2013T4, illustrating the strong morphological asymmetry of the iceberg. Elevations were calculated using the same geoid reference as REMA; therefore, the values do not represent absolute elevations and should be interpreted only in a relative sense.<\/p>\n Notably, a narrow passage of approximately 1\u2009km intermittently persisted along the eastern margin between the iceberg and Coulman Island (see Fig.\u00a01c<\/a>). This corridor was not fully obstructed and may have allowed limited movement between the colony and offshore waters. However, accessing this passage likely required substantial lateral movement along the iceberg margin, increasing travel distance and time. Given the asymmetric slope configuration, individuals approaching along the gently sloping western face may have been directed toward the impassable southern escarpment, thereby increasing travel time before locating the ~1\u2009km-wide eastern opening, as inferred from satellite imagery.<\/p>\n Even where access remained possible via the eastern corridor, the spatial configuration of the fast-ice edge suggests that commuting distances between the colony and open water were longer than in previous years, increasing from approximately 9.3\u2009km in 2024 to 14.9\u2009km in 2025 based on satellite-derived geometry (Fig.\u00a05a<\/a>). However, this represents a minimum estimate assuming direct access, and actual travel distances were likely substantially greater due to route-finding behavior. Although access was not entirely blocked, the combined configuration of the grounded iceberg and surrounding sea ice likely increased navigational complexity, potentially forcing individuals to follow indirect or suboptimal paths. Penguins rely on visual cues and learned spatial memory for navigation40<\/a>,41<\/a>, although the extent to which this applies under highly altered icescape conditions remains uncertain, and such cues may have been partially obscured or disrupted in this setting.<\/p>\n Fig. 5: Schematic of iceberg-induced obstruction and altered access pathways at the Coulman Island emperor penguin colony. a Sentinel-1 SAR imagery acquired on 21 August 2025 (WGS 1984 UTM Zone 59S) showing the spatial configuration of the fast-ice edge and inferred access routes. The blue line indicates the fast-ice edge in 2025, and the red line that of 2 August 2024. The colony is marked by a yellow circle, with concentric dashed circles indicating distances of 5, 10, and 15\u2009km. The green solid line represents the estimated commuting route to open water in 2025, while the green dashed line indicates the equivalent route in 2024. b Conceptual illustration of how a grounded iceberg modified terrestrial access routes between the Coulman Island emperor penguin colony and the adjacent sea. c Oblique view of the ocean-facing flank of the iceberg, where it sloped gently, enabling access for the penguins. d The colony-facing flank, showing a\u2009~\u200921.7\u2009m ice cliff that was impassable for the penguins.<\/p>\n Field observations documenting adult penguins remaining in prolonged stasis along the southern ice walls (Fig.\u00a05b\u2013d<\/a>; Supplementary Fig.\u00a01<\/a>) are consistent with restricted, spatially heterogeneous access pathways at the time of observation. While rerouting through the eastern corridor cannot be excluded, the observed spatial concentration of individuals suggests that access constraints were non-uniform and likely imposed differential movement costs, particularly in terms of increased travel time and energetic expenditure, across the iceberg perimeter11<\/a>,29<\/a>.<\/p>\n Consequently, delays in locating or navigating limited-access corridors during early chick rearing could reduce provisioning frequency to newly hatched chicks42<\/a>,43<\/a>. Such topographically induced delays are particularly consequential during this period, when provisioning schedules are tightly constrained, and energetic margins are narrow. Following hatching, emperor penguin chicks can survive only for a limited period on esophageal secretions (penguin milk) provided by the incubating male44<\/a>,45<\/a>. Even modest increases in travel time may therefore translate into a disproportionate increase in chick mortality risk8<\/a>,11<\/a>.<\/p>\n Taken together, these results indicate that the impact of the grounded iceberg cannot be attributed to a single mechanism, but rather to the combined effects of increased commuting distance and navigation disruption. While access to open water was not entirely prevented, the asymmetric configuration and limited openings likely reduced the efficiency and predictability of movement between the colony and foraging areas. This interpretation highlights the importance of local geometric constraints in shaping ecological outcomes and provides a basis for comparison with previously documented iceberg-related disturbances.<\/p>\n Comparison with previous events and mechanisms<\/p>\n The 2025 reduction in breeding output at Coulman Island differs from previously documented declines at this colony and elsewhere16<\/a>,34<\/a>,36<\/a>. Long-term monitoring has recorded substantial interannual variability in chick numbers, including declines of approximately 46% in 1993 and over 50% in 2010 Fig.\u00a03<\/a>;34<\/a>,36<\/a>. The 2010 event was accompanied by reduced adult attendance and interpreted as reflecting adult decisions to forego breeding, attributed to insufficient energetic reserves16<\/a>. The rapid recovery of adult numbers by 2011 supports the view that this episode primarily reflected a temporary breeding suspension rather than large-scale mortality.<\/p>\n In contrast, the 2025 pattern suggests that many adults initiated breeding but experienced early-stage reproductive loss. Evidence includes continued adult presence at the colony alongside a relatively low chick-to-adult ratio (0.44). This pattern is more consistent with disrupted chick rearing than with pre-breeding abstention16<\/a>, indicating an extrinsic physical cause rather than intrinsic life-history trade-offs.<\/p>\n A comparison with previously documented iceberg-related events further clarifies this mechanism29<\/a>. At Cape Crozier, reduced output resulted from the destruction of fast-ice breeding habitat. At Beaufort Island, habitat remained intact, but access routes were obstructed, requiring extended detours that disrupted provisioning. The 2025 Coulman Island event most closely resembles the Beaufort Island mechanism, with one important difference: the semi-enclosed coastal geometry (see Fig.\u00a01<\/a>) likely restricted alternative access routes. Unlike multi-year iceberg systems such as B15-A and C16, which exerted prolonged and large-scale ecological impacts, the event described here was shorter-lived and spatially confined. Accordingly, its impact should be interpreted as a localized, event-driven disturbance rather than a persistent, system-scale forcing. The iceberg\u2019s asymmetric configuration, with a gently sloping ocean-facing surface, likely directed returning adults toward an impassable southern escarpment, compounding movement costs (Fig.\u00a05b\u2013d<\/a>).<\/p>\n Evidence collected during the 2025 field season suggests that the demographic consequences of the iceberg event were concentrated on chick productivity. Flipper length and body mass were measured in 37 surviving chicks during December and showed no significant differences relative to chicks at Cape Washington, consistent with adequate provisioning among individuals that survived the early post-hatching period. No adult carcasses were observed during ground visits, although adult mortality could not be directly assessed. Access to the colony, while severely constrained by the iceberg, was not entirely blocked. Taken together, these observations indicate that the most evident demographic consequence of the 2025 event was reduced chick productivity.<\/p>\n One plausible explanation is that survival reflected heterogeneity in parental access and foraging success. Some adults may have located and repeatedly used alternative routes earlier than others, allowing them to continue provisioning their chicks despite the access constraints. Because surviving chicks did not differ markedly in body mass or flipper length from chicks at Cape Washington, the available data do not support a strong developmental-stage or body-condition bias among survivors.<\/p>\n Future perspectives: event-driven risks in a changing Ross Sea<\/p>\n The 2025 Coulman Island event is better interpreted as a localized, event-driven disturbance rather than as evidence of persistent risk to emperor penguins across the Ross Sea. While the Ross Sea region has historically exhibited relatively stable sea-ice conditions19<\/a>,21<\/a>, recent variability suggests caution in generalizing its role as a refuge. This event highlights a class of event-driven disturbances that may not be fully represented in demographic models focused on large-scale mean-state variables, such as regional sea-ice extent.<\/p>\n The drift and grounding pathway of the 2025 iceberg highlights the importance of timing and spatial configuration in shaping ecological outcomes. Unlike iceberg C-33, which transited the Coulman Island sector in October 2016 and did not ground46<\/a>, the 2025 iceberg remained in proximity to the island and subsequently became grounded (Supplementary Fig.\u00a06<\/a>). To our knowledge, this represents the first documented case, based on satellite-era observations, of an iceberg grounding immediately north of the colony, despite multiple icebergs transiting the region without grounding. The processes controlling this behavior are not fully resolved and may involve interactions among sea ice, ocean forcing, and local bathymetry.<\/p>\n Increasing instability of Antarctic ice shelves over recent decades has been linked to iceberg calving events47<\/a>,48<\/a>,49<\/a>, potentially associated with climate-driven change such as ocean warming30<\/a>,31<\/a>. Large icebergs that remain grounded near the coast for extended periods can disrupt access routes to foraging areas and influence breeding outcomes at the colony scale. However, individual iceberg events are inherently stochastic, and our findings should be interpreted as evidence of a potential mechanism rather than a dominant driver of population change.<\/p>\n Emperor penguin responses to environmental change are likely nonlinear, emerging from interactions among sea ice, prey availability, episodic disturbance, and colony-level movement responses18<\/a>,50<\/a>. Although inter-colony connectivity and behavioral flexibility may buffer populations at the metapopulation scale12<\/a>,51<\/a>,52<\/a>, this flexibility does not preclude severe local reproductive collapse when accessibility abruptly declines at critical stages of the breeding cycle.<\/p>\n Future assessments of emperor penguin breeding prospects would benefit from accounting for the potential influence of stochastic iceberg\u2013sea-ice interactions, including calving timing, drift pathways, grounding probability, and residence time near breeding sites11<\/a>,52<\/a>. These processes represent low-frequency but high-impact disturbances that may affect local breeding outcomes under otherwise favorable regional sea-ice conditions. Additional factors, including coastal configuration and variability in fast-ice conditions, may further modulate colony vulnerability, although their specific contributions to the 2025 event remain uncertain. Addressing these processes will likely require continued long-term, cross-disciplinary monitoring, rather than direct incorporation into existing modeling frameworks, given their complexity.<\/p>\n","protected":false},"excerpt":{"rendered":"Restricted accessibility and its potential role in reduced chick productivity We define this process as \u201crestricted accessibility,\u201d in…\n","protected":false},"author":2,"featured_media":570178,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[8732,6823,242,5563,3181,85,46,141,386],"class_list":["post-570177","post","type-post","status-publish","format-standard","has-post-thumbnail","category-wildlife","tag-earth-sciences","tag-ecosystem-ecology","tag-environment","tag-environmental-impact","tag-general","tag-il","tag-israel","tag-science","tag-wildlife"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/570177","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=570177"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/570177\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/570178"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=570177"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=570177"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=570177"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"Fig.](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2026\/08\/43247_2026_3764_Fig4_HTML.png\")
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