I'm not quite in the subject, but I've heard that the Norwegians have a database of Colonies

Hi, I think that dr. Stefano Volponi can give you information on this topic

Hi, this from Cornell Labs Birds of N America. in case you don't already have it. There is far more info there on these subjects. Needs an annual sub for full access but well worth it. You also get the excellent HBW Alive included. Best wishes Peter

First/Only Brood Per Season One brood/yr. Peak egg-laying in early to mid-Apr, with earliest 22 Mar, latest 28 Apr (Hand 1980a, Levalley 1975, Spear and Anderson 1989, Carmona and Zárate 1992, Tershy et al. 1992, Carmona 1993, Zárate 1995). Incubation probably begins with first egg; lasts 3.5–4 wk (±28 d on average; Carmona 1993), with hatching by early May (Carmona 1993). First fledglings appear by early Jun (Zárate 1995). Chicks cared for up to 6 mo after leaving territory.

Pair digs various scrapes, but female chooses ultimate nest site by where she lays eggs (Hand 1979b). Access to water critical (for thermoregulation). Predation pressure apparently selects for choice of nest site with greater-than-average visibility of surroundings; colonial nesting also likely a result of predation pressure (Hand et al. 1981, Spear and Anderson 1989; see Habitat: breeding range, above). Noncolonial breeders more susceptible to predation by Common Ravens, but less susceptible to predation by humans, suggesting a potential selective trade-off in nest-site selection (Spear and Anderson 1989).

Nests placed within 30 m of high-tide line in rows roughly paralleling shoreline, typically just below first line of vegetation; occasionally placed in rocky areas (Levalley 1975, Hand et al. 1981, Spear and Anderson 1989). Colonial pairs prefer beach-berm over talus-boulder, occasionally grass and boulder-beach; noncolonial pairs show no substrate preference (Hand et al. 1981, Spear and Anderson 1989). Because of heat stress (see Food habits: metabolism and temperature regulation, above), sites nearly always located near water and shaded; wind exposure less important. Colonial birds prefer good landward visibility and wide seaward angle; noncolonial birds more consistently choose southerly aspect (Spear and Anderson 1989; see Habitat: breeding range, above).

Modal clutch size 3 (mean = 2.5-2.75; Levalley 1975, Carmona and Zárate 1992, Carmona 1993, Zárate 1995). Many birds, 26% in one study, lay only 2 eggs, and more than 12% lay only 1 (Zárate 1995). Some birds lay 4 or even 5 eggs on rare occasion (perhaps 1% of nests); no evidence for 2 females sharing nest in this species, but this possibility could account for large clutches, particularly clutch of 8 eggs recorded by Hand (Hand 1980a). Only 1 successful brood/season because fledging takes between 15 and 20 wk. Replacement clutches laid if early clutches destroyed. Nest complete or nearly so before first egg laid. Eggs probably laid in morning. Clutches generally take 5–6 d to complete, but eggs laid 1–5 d apart, with 2–3 d separation on average (Zárate 1995). Male feeds female regularly throughout laying period. Female rarely leaves territory during this time, but male frequently absent obtaining food. Female resists forced copulation attempts. Replacement clutches likely have smaller or fewer eggs than originals. Intraspecific nest parasitism and egg-dumping not recorded; chick adoption common in Western Gull (Pierotti and Annett 1995) and occurs in Yellow-footed Gull.

Estimated 20,000 breeding pairs in Gulf of California (Anderson Anderson 1980, Anderson 1983a, Wilbur 1987); these estimates, however, based on qualitative assessments only. No formal population estimate published, although transect survey data have been gathered (but not analyzed) in Gulf of California (R. L. Pitman unpubl. data). No records in U.S. until mid-1960s. Postbreeding visitors to Salton Sea, CA, numbered nearly 50 individuals by 1970; now recorded annually there in hundreds, with maximum near 1,000 individuals. Numbers have increased steadily at Salton Sea in past decade (see Distribution: historical changes, above). Trends in Gulf of California unknown. Increased dispersal to Salton Sea may reflect (1) larger population size in Gulf, (2) decreased breeding success with concomitant increase in dispersal (i.e., changes in cost-benefit ratio with regard to food availability, weather conditions, etc.), (3) a learned behavior increasing in frequency, or (4) some combination of these factors.

For a more recent population estimate: 60 000 individuals in 2015, try

Wetlands International (2015). Waterbird Population Estimates. http://wpe.wetlands.org/.

best wishes for the new year

Peter

Hi guys, thanks for answer my cuestion, that has been so helpfully.

Roberto Pollo, I'll try to contact with Dr. Stefano Volponi.

Peter Flin, so many thanks for taking the time to senme that kind of information about the YFGU, is exactly what I needed. I'm gonna read the document that you send me about the recent population estimate.

Hi.

It's not a digital platform, but you can see different publications about such topics visiting the website of the journal SEABIRDS; see:

http://www.seabirdgroup.org.uk/publications

Best regards.