Breeding

Gonadal activity can be different in different years, with a peak in October–December (37 Cikutovic, M. A., C. G. Guerra, and L. C. Fitzpatrick (1988). Gonadal cycle of Gray Gulls Larus modestus in northern Chile. Gerfaut 78:209-216. Close ). Adults copulate between August–February, and the egg-laying occurs between the end of November and mid-January (25 Aguilar R., M. Perucci, T. Cisternas, M. Torres, M. Silva, A. Marín, A. Silva, and P. Bolados (2013). La nidificación de la Gaviota Garuma y su vulnerabilidad a las actividades antrópicas en el Desierto de Atacama. CULTAM. Technical report. Close , 19 Medrano, F. (2018). Gaviota garuma. In Atlas de las Aves Nidificantes de Chile (F. Medrano, R. Barros, H. Norambuena, R. Matus, and F. Schmitt, Editors), Red de Observadores de Aves y Vida Silvestre de Chile, Santiago, Chile. pp. 234-235. Close ). In one colony visited over three different seasons, egg laying began at different times each season: mid- to late November, early December, and early January (21 Goodall, J. D., R. A. B. Philippi, and A. W. Johnson (1945). Nesting habits of the Peruvian Gray Gull. Auk 62(3):450-451. Close , 3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ). Howell et al. (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ) also noted that within a colony, egg-laying was not synchronous, and extended over about a three-week period.

Microhabitat

One way Gray Gull manages water loss and overheating of eggs and chicks is to choose breeding sites that have medium-sized rocks, where the small chicks look for shelter from the sun (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close , 38 Fitzpatrick, L. C., C. G. Guerra, and R. E. Aguilar (1989). Microclimatic features of Gray Gull Larus modestus nests in the Atacama Desert. Gerfaut 78:421-428. In German. Close ). Despite the importance of these rocks, nests do not seem to be placed directly besides rocks (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Site Characteristics

The species breeds in the Atacama Desert up to 115 km from the coastline (21 Goodall, J. D., R. A. B. Philippi, and A. W. Johnson (1945). Nesting habits of the Peruvian Gray Gull. Auk 62(3):450-451. Close , 39 Howell, T. R. (1982). Desert-nesting sea gulls. Natural History 91: 52-59. Close , 20 Aguilar-Pulido R., C. Catoni, G. Luna-Jorquera, M. Perucci, G. Dell'Omo, C. Zavalaga, and A. Simeone (2021). Distribución, características y situación actual de las colonias reproductivas de la Gaviota garuma (Leucophaeus modestus) en el desierto de Atacama, Norte de Chile. Revista Chilena de Ornitología 27:21-36 Close ). In these areas, the air temperatures usually reach over 30°C (30 Malinarich, V. (2016). Diagnóstico poblacional de la gaviota garuma Leucophaeus modestus (Tschudi, 1843), en la Zona Norte de Chile. Unidad de Recursos Naturales Renovables. Servicio Agrícola y Ganadero (SAG), Región de Tarapacá Report. 39 pp. Close ), and eventually up to 40°C (FM and RS, personal observation). The reasons for this behavior are unclear, but it has been proposed that this is to avoid predation (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ). The gull breeds either in aggregated colonies (with up to 20,000 breeding pairs) or in scattered isolated nests (20 Aguilar-Pulido R., C. Catoni, G. Luna-Jorquera, M. Perucci, G. Dell'Omo, C. Zavalaga, and A. Simeone (2021). Distribución, características y situación actual de las colonias reproductivas de la Gaviota garuma (Leucophaeus modestus) en el desierto de Atacama, Norte de Chile. Revista Chilena de Ornitología 27:21-36 Close ). The location of both the colonies and isolated nests is mobile (22 Devillers, P., and J. A. Terschuren (1976). Desertion of the Grey Gull (Larus modestus) colony of Pedro de Valdivia (Chile). Gerfaut 66:132-137. Close , 20 Aguilar-Pulido R., C. Catoni, G. Luna-Jorquera, M. Perucci, G. Dell'Omo, C. Zavalaga, and A. Simeone (2021). Distribución, características y situación actual de las colonias reproductivas de la Gaviota garuma (Leucophaeus modestus) en el desierto de Atacama, Norte de Chile. Revista Chilena de Ornitología 27:21-36 Close ). Colonies can move to completely new locations after just a few years, making it hard to plan their protection; this has been attributed to years with low-food availability (22 Devillers, P., and J. A. Terschuren (1976). Desertion of the Grey Gull (Larus modestus) colony of Pedro de Valdivia (Chile). Gerfaut 66:132-137. Close , 17 Aguilar, R., A. Simeone, J. Rottmann, M. Perucci, and G. Luna-Jorquera (2016). Unusual coastal breeding in the desert-nesting Gray Gull (Leucophaeus modestus) in northern Chile. Waterbirds 39(1):69–73. Close ).

Known colonies have an area, ranging from 0.01 km² to 9.2 km² (20 Aguilar-Pulido R., C. Catoni, G. Luna-Jorquera, M. Perucci, G. Dell'Omo, C. Zavalaga, and A. Simeone (2021). Distribución, características y situación actual de las colonias reproductivas de la Gaviota garuma (Leucophaeus modestus) en el desierto de Atacama, Norte de Chile. Revista Chilena de Ornitología 27:21-36 Close ), and the number of pairs consist of between 12–30,000 breeding pairs (20 Aguilar-Pulido R., C. Catoni, G. Luna-Jorquera, M. Perucci, G. Dell'Omo, C. Zavalaga, and A. Simeone (2021). Distribución, características y situación actual de las colonias reproductivas de la Gaviota garuma (Leucophaeus modestus) en el desierto de Atacama, Norte de Chile. Revista Chilena de Ornitología 27:21-36 Close ). Furthermore, there is no relationship between the distance from the coast and the colony size (20 Aguilar-Pulido R., C. Catoni, G. Luna-Jorquera, M. Perucci, G. Dell'Omo, C. Zavalaga, and A. Simeone (2021). Distribución, características y situación actual de las colonias reproductivas de la Gaviota garuma (Leucophaeus modestus) en el desierto de Atacama, Norte de Chile. Revista Chilena de Ornitología 27:21-36 Close ).

Construction Process

In one colony, both members of a pair would construct the nest, and was described as such: "scrapes were definitely being formed by rubbing the breast feathers in the sand and pushing posteriorly with the feet... both birds were involved in scrape-making, with each bird working on each of the scrapes at one or another time" (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ). Multiple nests may be constructed within the small territory before one is selected for egg-laying (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Structure and Composition

The nest is a little bowl in the sand of the desert, without additional material (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ). They are located in flat areas. In one colony, nests were constructed in a variety of substrates, including soft and powdery sand to loose small stones (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Dimensions

In one study, nests measured 200–230 mm in diameter and 35 mm deep (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Shape

The pores in the eggshells are smaller than expected for this size of gull, and this is understood as an adaptation to avoid the loss of water in the middle of the most arid desert in the world (40 Guerra, C. G., R. E. Aguilar, and L. C. Fitzpatrick (1988). Water vapor conductance in Gray Gulls (Larus modestus) eggs: adaptation to desert nesting. Colonial Waterbirds 11(1):107-109. Close ). As a handicap, this adaptation reduces the oxygen exchange with the environment, which produces a protracted incubation period (41 Monge, C. C., H. Ostojic, R. Aguilar, and V. Cifuentes (2000). Reduced oxygen diffusion across the shell of Gray gull (Larus modestus) eggs. Biological Research 33:209-214, Close ).

Size

Egg length, 58.3 ± 0.57 mm (n = 14; 21 Goodall, J. D., R. A. B. Philippi, and A. W. Johnson (1945). Nesting habits of the Peruvian Gray Gull. Auk 62(3):450-451. Close ); egg width, 41.3 ± 0.28 mm (n = 14; 21 Goodall, J. D., R. A. B. Philippi, and A. W. Johnson (1945). Nesting habits of the Peruvian Gray Gull. Auk 62(3):450-451. Close ).

Mass

Mean egg mass in one colony was 51.8 g (range 42–62 g, n = 89 eggs). In clutches with two eggs, one egg was almost always larger than the other, and the mean difference in mass was 5.2 g (n = 23 clutches) (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Color and Surface Texture

Eggs have been described as ivory-colored with reddish spots, especially near the base; in one study, eggs were described as sometimes approaching pale ochraceous salmon in base color (42 Johnson, A. W. (1967). The Birds of Chile and Adjacent Regions of Argentina, Bolivia and Peru. Volume 2. Platt Establecimientos Gráficos, Buenos Aires, Argentina. Close ). Some eggs have been described as being very faintly spotted (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Clutch Size

In one colony, most nests had 1 egg (39.2% of the nests) or 2 eggs (59.8% of the nests), but a small number can have 3 or 4 eggs (20 Aguilar-Pulido R., C. Catoni, G. Luna-Jorquera, M. Perucci, G. Dell'Omo, C. Zavalaga, and A. Simeone (2021). Distribución, características y situación actual de las colonias reproductivas de la Gaviota garuma (Leucophaeus modestus) en el desierto de Atacama, Norte de Chile. Revista Chilena de Ornitología 27:21-36 Close ). In another colony, 52% of nests had 1 egg, 47% had 2 eggs, and 1% had 3 eggs (n = 182 nests) (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Onset of Broodiness and Incubation in Relation to Laying

Incubation begins with the laying of the first egg (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Incubation Period

Incubation usually takes 29–30 d (43 Aguilar R., L. C. Fitzpatrick, C. G. Guerra, and G. S. Luna (1994). Time and temperature of incubation and egg hatching success in Gray gull Larus modestus at Lealtad (northern Chile) nesting site. Estudios Oceanológicos 13: 1-11. Close ), but can take up to 32 d (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Parental Behavior

During incubation, one of the parents stays at the nest during the day to shade the eggs to avoiding overheating (36 Aguilar, R., C. G. Guerra , L. C. Fitzpatrick, and G.S. Luna-Jorquera (1998). Thermobiology of Gray Gull (Larus modestus) embryos and hatchlings: correlates of nesting in the Atacama Desert. Estudios Oceanológicos 17:7–12. Close ). The switch of incubation duties between parents happens during the night (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close , 43 Aguilar R., L. C. Fitzpatrick, C. G. Guerra, and G. S. Luna (1994). Time and temperature of incubation and egg hatching success in Gray gull Larus modestus at Lealtad (northern Chile) nesting site. Estudios Oceanológicos 13: 1-11. Close ). In a study of one colony, adults sat on eggs during the night, and would stand to shade the eggs by midday or early afternoon; during windy events, birds would sit on their eggs even during the day, as the wind would cool the eggs significantly (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Hardiness of Eggs Against Temperature Stress: Effect of Egg Neglect

Attended eggs were maintained at a temperature between 33–38°C (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ). Eggs that were left unattended and exposed to the sun during the day reached internal temperatures above 44°C, which has been shown to be lethal for chicken eggs (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Preliminary Events and Vocalizations

In one study, eggs hatched 2–3 d after the first pip appeared (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Shell Breaking and Emergence

Howell et al. (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ) found that in two egg clutches, hatching was not synchronous, and that the second chick would hatch 1–2 d after the first chick hatched.

Growth and Development

Chicks are pale gray (occasionally buffy), with obscure black spots on sides of their head, throat, back, and flanks. In one colony, at hatching, chicks had a mean mass of 34 g (range of 31–38 g, n = 8; 3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ). The chick's growth takes 60–70 d before fledging (44 Guerra, C. G., L. C. Fitzpatrick, and R. E. Aguilar (1988). Growth rates in Gray Gulls Larus modestus: influence of desert nesting and foraging distance. Auk 105:779-783. Close ). In one study, Guerra et al. (44 Guerra, C. G., L. C. Fitzpatrick, and R. E. Aguilar (1988). Growth rates in Gray Gulls Larus modestus: influence of desert nesting and foraging distance. Auk 105:779-783. Close ) found that tarsus length increased fastest, and reached an asymptote in growth rate after 50 d, while culmen length increased at a steady rate until it reached an asymptote at 100 d.

Brooding

After hatching, the parents stay on the nest during the day for the first ten days (44 Guerra, C. G., L. C. Fitzpatrick, and R. E. Aguilar (1988). Growth rates in Gray Gulls Larus modestus: influence of desert nesting and foraging distance. Auk 105:779-783. Close ). When at the nest, adults provide shade to chicks to keep them from overheating (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ). At one colony, adults were seen to attack chicks, including their own, that were close to but outside of the nest; chicks would respond by performing a submissive display, where they would crouch and point its bill down, after which point adults would usually stop attacking. Once a chick reached the nest and was under an adult, the adult would brood or provide shade to the chick. Any chick that reaches a nest under an adult would be brooded, not just the parent's chick (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Feeding

Chicks are primarily fed Peruvian anchovy (Engraulis ringens) and Pacific mole crab (Emerita analoga) (44 Guerra, C. G., L. C. Fitzpatrick, and R. E. Aguilar (1988). Growth rates in Gray Gulls Larus modestus: influence of desert nesting and foraging distance. Auk 105:779-783. Close ). Parents return to the nest at night to feed chicks. One adult returning to the colony was carrying about 40 g of food in the lower esophagus and proventriculus. In one study, adults were found to regurgitate at least some food immediately upon returning to the nest site, and may regurgitate food over the course of the entire night, sometimes even into the morning. Chicks would either eat food from the ground, or eat food that was passed directly to them by the adult (3 Howell, T. R., B. Araya, and W. R. Millie (1974). Breeding biology of the Gray Gull, Larus modestus. University of California Publications in Zoology 104:1-57. Close ).

Does not exhibit cooperative breeding.

Its nests are not parasitized by other birds.

When fledglings leave the nests, they fly on their own to the sea.

Information needed.