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10 GREAT BLUE HERON
<br />Microclimate. No information.
<br />Maintenance or reuse of nests, alternate nests.
<br />Nests often reused for many years. Twigs gathered
<br />near nest (Pratt 1970) by male (mostly when eggs
<br />are laid and hatched) and placed by female
<br />(Brandman 1976). May build new nest if early
<br />attempt fails (Pratt 1970).
<br />EGGS
<br />Shape. Eggs of Great Blue and Great White
<br />herons similar (Bent 1926). Oval to long oval, long
<br />elliptical or subelliptical (Harrison 1978).
<br />Size. Length 50.7 to 76.5 mm; breadth 29.0 to
<br />50.5 mm (Bent 1926). Mean length 61.38 to 65.57
<br />mm, breadth 45.07 to 46.49 mm for 5 subspecies
<br />described by Palmer (1962). Similar dimensions (6
<br />subspecies) described by Butler (1989); volume 6.3
<br />to 7.0 cm3, estimated fresh weight 67.7 to 79.9 g.
<br />Fresh weight in Nova Scotia: 70.4 g in 1977 (SD =
<br />3.8, range 63.5 -79.5, n = 27) and 71.6 g in 1978 (SD
<br />= 4.1, range 61.0 -78.0, n = 34; Quinney and Smith
<br />1979). Miniature eggs rarely laid; one from British
<br />Columbia 35 x 45 mm (RWB).
<br />Eggshell composition. The average concen-
<br />tration of calcium in 8 eggshells from the Columbia
<br />River, WA, 37.3% (Rickard and Schuler 1990). The
<br />average concentration (ug /g) in the same 8 eggs
<br />was 6.7 Zn, 170 Sr, 190 Ba, 48 Fe and 9.0 Cu.
<br />Color. Dull pale blue; fades slightly with age.
<br />See Harrison (1978).
<br />Surface texture. Smooth or slightly rough.
<br />Egg laying. Eggs laid mostly at 2 d intervals,
<br />occasionally 3 d (Vermeer 1969; Pratt 1970,
<br />McAloney 1973).
<br />INCUBATION
<br />Onset of broodiness and incubation in relation
<br />to laying. Incubation by male and female (Pratt
<br />1970, Brandman 1976, Mock 1979) began after first
<br />egg was laid in California (Pratt 1970).
<br />Incubation patch. No information.
<br />Incubation period. About 27 d: Alberta, mean =
<br />26.7 d (range 26-27, n = 6 clutches, Vermeer 1969);
<br />California, 25, 28, 29, and 29 d (Pratt 1970); Nova
<br />Scotia, mean = 27.1 d (range 25-30 d, n =11 nests;
<br />McAloney 1973).
<br />Parental behaviour. Bouts long; male on nest
<br />an average of 10.4 h each day, females 3.5 h/d (n
<br />= 7 nests; Brandman 1976). Females generally
<br />incubate at night. Adults average 54 min / h sitting
<br />on eggs (Pratt 1970). Eggs rolled by parent an
<br />average of once every 2 h (Pratt 1970).
<br />Hardiness of eggs. No information.
<br />HATCHING
<br />Preliminary events and vocalizations. No
<br />information.
<br />A. Poole, P. Stettenheim, and F. Gill, Editors
<br />The Birds of North America, No. 25, 1992
<br />Shell breaking and emergence. Chicks take 48 h
<br />or less to become completely free from egg
<br />(Quinney 1982). Time between hatching of first
<br />and last eggs (when all eggs hatched) ranged from
<br />2 to 6 d (mean = 3 d; McAloney 1973) and 4 to 8 d
<br />(Quinney and Smith 1979) in Nova Scotia, 5 to 8 d
<br />in California (Pratt 1970, Brandman 1976). Some
<br />hatch on same day (Quinney 1982). In Texas, first
<br />egg hatches an average 1.6 d before second egg
<br />which hatches 1.7 d before third, which in turn
<br />hatches 1.9 d before fourth egg (Mock 1978a).
<br />Parental assistance and disposal of eggshells.
<br />Adults throw most eggshells from nests soon after
<br />hatching (Brandman 1976, Bayer 1982, Butler
<br />1989,1991).
<br />YOUNG BIRDS
<br />Condition at hatching. Semi - altricial; back,
<br />head, and sides of Great Blue chicks covered in
<br />pale gray down, especially bushy on crown
<br />(Harrison 1978). Wings, bill, and legs pinkish gray
<br />and mostly unfeathered. Eye bluish and open.
<br />Calling (sounds like tik- tik -tik) commences within
<br />minutes of leaving the egg. Mean weight at
<br />hatching in 2 Nova Scotia colonies: 49.3 g (SD = 3.2,
<br />n = 5) and 51.8 g (SD = 7.1, n = 39; Quinney and
<br />Smith 1979). Great White chicks covered in white
<br />down at hatching.
<br />Growth and development. Mass increase.
<br />Quinney (1982) weighed and measured growth of
<br />chicks up to 30 d of age. Last hatching chicks grew
<br />slower than earlier hatching nestmates. Mass
<br />increase was nearly linear in first 30 d of age. No
<br />measurable sexual dimorphism at least before
<br />28.5 d. Sixteen 45-d -old chicks weighed 86% of
<br />adult weight. Asymptote of growth curve of hand -
<br />reared chicks was 2.3 kg (D. Bennett pers. comm.).
<br />Growth of body parts. Culmen, tarsus, proximal
<br />wing length, wing chord and length of tenth
<br />primary increase linearly. However, growth over
<br />the entire nestling period is probably best explained
<br />by logistic growth curve (Quinney 1982). Control
<br />of body temperature: Little information. Gular
<br />pouch fluttering at 18 d (Pratt 1970) positively
<br />correlated with ambient temperature (Dowd and
<br />Flake 1985a). Sunbathe at 27 d (Pratt 1970). Behavior
<br />and locomotion. Described by Pratt (1970) and
<br />Dowd and Flake (1985a). Preening starts at 6 d of
<br />age, stagger to their feet at 14 d and walk steadily
<br />at 21 d. Brood reduction, prevalent in many nests,
<br />proposed to be the outcome of aggression
<br />precipitated by size of prey items delivered to
<br />chicks by parents (Mock 1985, 1986, 1987). Wing -
<br />flapping starts in fourth week and short hops
<br />made into branches near nest at 7 wk. Sustained
<br />flights begin at 60 d. Recognizes parents
<br />approaching colony at 9 wk. Depart nest at mean
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