Vision on the high seas: spatial resolution and optical sensitivity in two procellariiform seabirds with different foraging strategies

Abstract

Procellariiform or 'tubenosed' seabirds are challenged to find prey and orient over seemingly featureless oceans. Previous studies have found that life-history strategy (burrow versus surface nesting) was correlated to foraging strategy. Burrow nesters tended to track prey using dimethyl sulphide (DMS), a compound associated with phytoplankton, whereas surface-nesting species did not. Burrow nesters also tended to be smaller and more cryptic, whereas surface nesters were larger with contrasting plumage coloration. Together these results suggested that differences in life-history strategy might also be linked to differences in visual adaptations. Here, we used Leach's storm petrel, a DMSresponder, and northern fulmar, a non-responder, as model species to test this hypothesis on their sensory ecology. From the retinal ganglion cell density and photoreceptor dimensions, we determined that Leach's storm petrels have six times lower spatial resolution than the northern fulmars. However, the optical sensitivity of rod photoreceptors is similar between species. These results suggest that under similar atmospheric conditions, northern fulmars have six times the detection range for similarly sized objects. Both species have extended visual streaks with a central area of highest spatial resolution, but only the northern fulmar has a central fovea. The prediction that burrow-nesting DMSresponding procellariiforms should differ from non-responding species nesting in the open holds true for spatial resolution, but not for optical sensitivity. This result may reflect the fact that both species rely on olfaction for their nocturnal foraging activity, but northern fulmars might use vision more during daytime.

Eye Size, Fovea, and Foraging Ecology in Accipitriform Raptors

“…S3). Such intraspecific differences have previously been observed in common buzzards [Oehme, 1964] and northern fulmars [Mitkus et al, 2016]. In addition to this variation, we also found that individuals may differ by the presence or absence of a rim around the foveal pit.…”

Development of the Visual System in a Burrow-Nesting Seabird: Leach's Storm Petrel

“…Van Buskirk and Nevitt [2008] have postulated that burrow-nesting procellariform species are likely to rely more on odour than visual tracking to locate prey at sea. Consistent with this finding, Mitkus et al [2016] have found that these birds have relatively low anatomical spatial resolution.…”

Olfactory receptor subgenome and expression in a highly olfactory procellariiform seabird

“…The larger number of intact OR genes and smaller percentage of pseudogenized ORs 467 in Leach's storm-petrels than most waterbirds suggests enhanced olfactory capabilities, 468 consistent with the large olfactory bulb ratio in Procellariiformes (Corfield, et reliance on olfaction and good sense of smell may develop in Leach's storm-petrels being 488 raised in darkness, whereas Procellariiform species exposed to more light may depend less on 489 olfaction for homing and individual recognition (Mitkus, et al 2016;Mitkus, et al 2018). 490…”

“…The Leach's storm-petrel indeed has six times lower visual spatial resolution than the 491 northern fulmar (Mitkus, et al 2016), which rely more on using vision than olfaction for 492 foraging (van-Buskirk and Nevitt 2008). By investigating the OR subgenome in this study, 493 our genomic and transcriptomic evidence confirms that the Leach's storm-petrel has superior 494 olfactory capabilities among waterbirds and birds in general.…”