Can birds count eggs in their nests?

Abstract

Sensory mechanisms controlling avian clutch size have diversified into distinct types, according to the nature of the input that is used to disrupt the growth of ovarian follicles and hence halt egg‐laying. In an article on brood parasitism, Lyon (2003) claimed that female American Coots Fulica americana can reduce their clutch size on the basis of visual cues in response to eggs laid in their nests by other females; in this species, therefore, egg counting would be used to control clutch size. After a close examination of the physiological determination of clutch size in American Coots, I show that seven of 17 parasitized clutches were smaller than the range controlled through the mechanism using an input to disrupt follicular growth (7–10 eggs per clutch). My reanalysis suggests that American Coots are incapable of adjusting clutch size via counting and re‐asserts that a species that can count eggs has yet to be found among birds that rely upon their own body heat for incubation.

Is it interspecific information use or aggression between putative competitors that steers the selection of nest‐site characteristics? A reply to Slagsvold and Wiebe

“…We suggest plausible mechanisms of assessment, which we acknowledge, requires further study. First, while the capacity for numerical estimation is most common in brood parasites (Haywood 2016), there is evidence for numerical ability in other birds too (Hunt et al 2008, Garland andLow 2014), even in this specific context of assessing clutch size to choose nest site (Odell and Eadie 2010). Male flycatchers may have capability to visually estimate egg number based on the size of the contrasting light area of pale eggs against dark nest linings or using tactile stimulation.…”

On the use of heterospecific information for nest site selection in birds

“…General assessments of clutch size in most birds is by tactile stimulation of the brood patch whereas the use of visual cues is documented only in a few obligate brood parasites (Haywood ). Unless flycatchers are unusual and have good visual counting ability, it will be the female, the sex that develops the brood patch in flycatchers, which will need to settle on, or physically contact, the tit eggs to ‘count’ them.…”

Cuckoos use host egg number to choose host nests for parasitism

“…That is whether female parasites know which nests are new and which nests have started incubation. Female cowbirds prefer a suitable number of eggs in their nests under lab condition (White et al 2007(White et al , 2009, and female American coots (Fulica americana) use visual cues to adjust clutch size and recognize foreign eggs suggesting that they can count eggs (Lyon 2003; but see Haywood 2016). In addition, evidence suggests that other bird species may have elaborate quantification skills (Hunt et al 2008;Odell and Eadie 2010;Bogale et al 2011;Scarf et al 2011;Nieder 2015, 2016).…”

“…Several bird species have elaborate quantification skills [14][15][16][17][18][19]. Female American coots (Fulica americana) use visual cues to adjust the clutch size and recognize foreign eggs, suggesting that they can count eggs ( [20]; but see [21]). Brood-parasitic female cowbirds, under laboratory conditions, prefer to lay eggs into host nests containing a suitable number of eggs [22,23], though a similar effect was not observed for great spotted cuckoos under field conditions [24,25].…”