Social status is associated with open-water gap crossing in an endangered marsh bird

<jats:p>Movement across gaps of unsuitable habitat can constrain functional connectivity, but gap permeability may vary with movement context and social status. Most thamnophilids are forest-understory birds reluctant to cross open areas. In contrast, &lt;i&gt;Formicivora acutirostris&lt;/i&gt; is one of only two marsh-dwelling thamnophilids, and open water constitutes a habitat gap for this endangered salt-marsh endemic. Previous observations documented water crossings of no more than 15 m and continuous flights of up to 25 m. We compared records of unpaired satellite individuals from 2001–2026 with 20 years of mapping of paired birds from 638 annual home-range/territory cycles involving 252 individuals. Records of four satellite individuals indicated 10 inferred water-gap crossings longer than 25 m, ranging from 27.0 to 183.0 m. For paired birds we identified three home-range gap crossings, and six territory gap crossings, in nine cycles (1.4%). Paired individuals crossed gaps of 2.9–31.4 m, and one territorial male was directly observed completing a continuous 45.3-m flight. These patterns were consistent with our predictions that paired birds would generally exclude water bodies from routine space use, whereas satellite individuals would be associated with wider crossings. Our observations suggest that water-gap permeability may be context dependent and that rare long-distance crossings may contribute to connectivity among marsh patches. This distinction cautions against inferring dispersal capacity from resident movements alone and highlights the potential role of closely spaced habitat patches as stepping stones.</jats:p>