Sexual dimorphism in morphology and plumage of endangered Yuma Ridgway’s Rails: a model for documenting sex

Many applications in wildlife management require knowledge of the sex of individual animals. The Yuma Ridgway’s Rail Rallus obsoletus yumanensis is an endangered marsh bird with monomorphic plumage and secretive behaviors, thereby complicating sex determination in field studies. We collected morphometric measurements from 270 adult Yuma Ridgway’s Rails and quantified the plumage and mandible color of 91 of those individuals throughout their geographic range to evaluate inter-sexual differences in morphology and coloration. We genetically sexed a subset of adult Yuma Ridgway’s Rails ( N =101) and used these individuals to determine the optimal combination of measurements (based on discriminant function analyses) to distinguish between sexes. Males averaged significantly larger than females in all measurements and the optimal discriminant function contained whole-leg, culmen, and tail measurements and classified correctly 97.8% (95% CI: 92.5-100.0%) of genetically sexed individuals. We used two additional functions that correctly classified ≥95.5% of genetically sexed Yuma Ridgway’s Rails to assign sex to individuals with missing measurements. These simple models provide managers and researchers with a practical tool to determine the sex of Yuma Ridgway’s Rails based on morphometric measurements. Although color measurements were not in the most accurate discriminant functions, we quantified subtle inter-sexual differences in the color of mandibles and greater coverts of Yuma Ridgway’s Rails. These results document sex-specific patterns in coloration that allow future researchers to test hypotheses to determine the mechanisms underlying sex-based differences in plumage coloration.

A Mycenaean pictorial vase from Midea

The Greek-Swedish excavations on the Mycenaean acropolis of Midea have brought to light a large amount of fine decorated pottery, which includes numerous fragmentary vases and sherds with pictorial decoration. This material has firmly established Midea as an important find-spot of figure-style pottery, like other great Mycenaean Argive centres, such as Mycenae, Tiryns and Berbati. This paper presents a remarkable pictorial vase recently found at Midea. It is a ring-based krater, almost completely restored from fragments, decorated with a row of six birds. The bird is a common motif in Mycenaean pictorial vase painting and also well attested on many other ceramic pieces at Midea, particularly the type of the folded-wing marsh bird. This type of bird is also popular at Tiryns, providing evidence that this category of pictorial pottery from the two citadels, dated to the LH IIIB2 period, was produced in the same workshop, which must have been situated at or near Tiryns. The abundant pictorial pottery from Midea and other significant discoveries at the site, such as monumental architectural remains and important finds, confirm the position of Midea as a great centre, alongside the other two Argive major citadels, Mycenae and Tiryns.

Habitat openness and edge avoidance predict Saltmarsh Sparrow abundance better than habitat area

The Saltmarsh Sparrow (Ammospiza caudacuta) is a tidal marsh bird facing rapid population decline throughout its range, largely caused by degradation and loss of breeding habitat. Thus, there is a need to preserve tidal marshes in the northeastern United States, but to do so requires an understanding of the habitat features that support robust populations. Previous studies have shown Saltmarsh Sparrow abundance increases with marsh size, but in similar bird species, area sensitivity is more directly linked to edge avoidance. Whether additional landscape features affect the abundance of Saltmarsh Sparrows is unknown. We explored how the height of objects on the horizon, an index of habitat openness, affected the abundance of Saltmarsh Sparrows. Our primary goal was to determine whether the angle to the highest point on the horizon (“angle to maximum horizon”) predicted abundance better than marsh area or distance to the marsh edge. We used N-mixture models to evaluate the combination of spatial factors that best predicted Saltmarsh Sparrow abundance while also accounting for survey-level variables that could influence detection probability. We found that the interaction between distance to edge and angle to maximum horizon best predicted abundance. Taller objects on the horizon were negatively correlated with bird abundance, and this effect was strongest within 50 m of the marsh edge. When we considered the predictive powers of patch area, distance to edge, and angle to maximum horizon individually, angle to maximum horizon was the best single predictor. We found the highest abundance of Saltmarsh Sparrows at point locations where the angle to maximum horizon was 0.0°, and at angles greater than 12° the predicted abundance fell below 1 bird per survey point. We propose that managers should prioritize marsh openness and experimentally test the effect of marsh edge manipulations when making conservation decisions for this rapidly declining species.