page_title: White-tailed eagle
section_title: Eggs and incubation
hierarchical_section_title: White-tailed eagle / Breeding / Eggs and incubation
caption_attribution_description: English&#x3a;&#32; Eggs of Haliaeetus albicilla groenlandicus collection of Jacques Perrin de Brichambaut.Français&#x202f;&#x3a;&#32; Œufs de Pygargue à queue blanche collection Jacques Perrin de Brichambaut.
context_page_description: The white-tailed eagle is a very large species of sea eagle widely distributed across temperate Eurasia. As are all eagles, it is a member of the family Accipitridae which includes other diurnal raptors such as hawks, kites, and harriers. One of up to eleven members in the genus Haliaeetus, which are commonly called sea eagles, it is also referred to as the white-tailed sea-eagle. Sometimes, it is known as the ern or erne, gray sea eagle and Eurasian sea eagle
  While found across a very wide range, today breeding as far west as Greenland and Iceland across to as far east in Hokkaido, Japan, they are often scarce and very spottily distributed as a nesting species, mainly due to human activities. These have included habitat alterations and destruction of wetlands, about a hundred years of systematic persecution by humans followed by inadvertent poisonings and epidemics of nesting failures due to various manmade chemical pesticides and organic compounds, which have threatened eagles since roughly the 1950s and continue to be a potential concern. Due to this, the white-tailed eagle was considered endangered or extinct in several countries.
context_section_description: Individual white-tailed eagles tend to be remarkably consistent on egg-laying times from year to year, seemingly regardless of surrounding weather conditions. Egg laying does vary of course by latitude. Historic breeders from Israel and Iran (where they still usually breed) were reported to lay eggs in January, while in Greece and the lower Volga river it is during February, in Germany mostly during March and in the subarctic of Lapland and northern Russia, to as late as late April to early May. White-tailed eagles in Scotland seem to have average egg laying about 3 weeks later, late March to early April, than those in coastal Norway. Even near Arctic in Finland, eggs were found as early as March 5 despite ranging often to as late as May. Younger pairs may nest later on average than older ones. In white-tailed eagles, many (perhaps a majority) of clutches consist of 2 eggs, especially in Irish and Scottish nests, with 3 egg clutches being considered uncommon to rare there. 4 egg clutches have been recorded on the Isle of Skye, as well as in at least Poland, Romania and Norway. Clutch size in Scotland averages 1.56, while in Norway it is 2.16. The eggs are a broad oval shape and dull white in colour, sometimes with a glossy sheen and are usually unmarked but for occasional yellowish stain. Fresh egg weigh from 120 to 148 g (4.2 to 5.2 oz),  with an average of approximately 135 g (4.8 oz) for the 1st egg and 124 g (4.4 oz) for the 2nd. If replacement clutch is laid, usually a single egg is laid which may weigh as little as 112 g (4.0 oz). Average egg dimension seem to keep in accordance with the female body size, smallest mean size known were from Turkey where the average dimensions were 71.8 mm × 56.2 mm (2.83 in × 2.21 in) to the largest in 3 surveys from Greenland, where they were 78 mm × 59.3 mm (3.07 in × 2.33 in). In 54 eggs from Scotland they ranged from 67.5 to 84.2 mm (2.66 to 3.31 in), averaging 75.8 mm (2.98 in), in height by 53.4 to 64 mm (2.10 to 2.52 in), averaging 58.7 mm (2.31 in), in width. In comparison, 90 eggs from mainland Europe ranged from 66 to 88.2 mm (2.60 to 3.47 in), averaging 73.4 mm (2.89 in), by 54 to 63.5 mm (2.13 to 2.50 in), averaging 57.6 mm (2.27 in). Eggs may be compromised quickly by frost and snow in relatively early clutches. Incubation starts as soon as the 1st egg is laid. In the species, a 2 to 3 day interval between the first and 2nd egg being laid (as well as hatching) is recorded. The female does up to 80-90% of incubation and all known nighttime incubating. However, in Norway, the male of a pair could contribute up to about 27% of incubation to daylight hours. There may be as many as 11 changes of the incubating individual within a day. The longest period recorded the clutch was unguarded was 20 minutes, although 1 pair perched nearby the nest without incubating for 48 minutes. The clutches in Norway left alone only 2-4% of the time. In some cases female may do all the incubation alone, however. When the female is off the nest, she sometimes kills prey and returns with a full crop, but prey capture during incubation is often up to the male. Late into incubation, shift changes decreases and the female will sit tight and will crouch down at the approach of a human rather than leave the nest. Calling and displaying are reduced during incubation, but occasionally both may leave the clutch and display still. The time range for incubation can vary from 34 to 46 days, but usually are between 38 and 42 days. A calculated mean time range for incubation of 38.3 days.
caption: egg, Haliaeetus albicilla groenlandicus - MHNT
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