[EBB Sightings] Back at Lake Merritt

For several years I led observation teams for SFBBO that monitored the
heron/egret/cormorant rookery at Lake Merritt each year. We definitely
observed double broods of chicks coming out of the same nest at times. The
only question is whether it was the same set of parents for both broods or,
as Hilary suggests, was the second brood raised by an opportunistic pair
that moved in when the first brood was fully fledged? I'd have to check back
through my records but I believe it's probable that the second batch of eggs
were being incubated while the first fledglings were still flapping around
on the adjacent branches, suggesting double clutching.

Bruce Mast
Oakland, CA
 
-----Original Message-----
From: sightings-bounces at diabloaudubon.com
[mailto:sightings-bounces at diabloaudubon.com] On Behalf Of Bob Power
Sent: Wednesday, August 29, 2007 1:35 PM
To: ebbsightings ebbsightings
Subject: Re: [EBB Sightings] Back at Lake Merritt

> Are the cormorants with young late breeders who lost
> out in the spring 
> land rush? Or multiple parents on their nth clutch
> of the season? Who 
> knows....

Hilary, Birds of North America on-line (worth it's
annual fee) thinks 2nd clutching is rare (for what
it's worth):

First brood per season
First eggs laid 2?4 wk after arrival: 2 wk in Alberta
(Vermeer 1969), 3 wk in Utah (Mitchell 1977), and 3?4
wk in Ontario (DVW). On Farallon Is., CA, egg-laying
generally starts late Mar (Ainley and Boekelheide
1990); occurs Apr?Sep in British Columbia (Campbell et
al. 1990); late Mar?late May in Utah (Mitchell 1977);
late Apr?Aug in Ontario (Peck and James 1983); from
about 10 May to Jul in St. Lawrence River estuary
(Lewis 1929). Most eggs in colony are laid within 2?3
wk of first clutch initiation, but timing is highly
variable among adjacent colonies (older colonies are
generally 2 or 3 wk ahead of new ones) and within
individual colonies. Will readily re-lay if first
clutch destroyed. Not unusual to have fresh eggs at
time of banding earliest young, mid- to late Jun on
Great Lakes (DVW).

Second brood per season
Second broods are rare. On Mandarte I., British
Columbia, 1 second clutch (containing 3 eggs) was
observed after first brood was raised (Drent et al.
1964); B?dard et al. (1995a) suggested that some pairs
raised 2 broods in Quebec. Not known if there are
double-brooded pairs in Florida, where cormorants
breed year-round (Kushlan and McEwan 1982).

Bob Power
Oakland, CA


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