Loon Magic/Loon Magic - Wayzata Technology (8011) (1993).iso/mac/mac text/09 Home - Eggs⁄Incubation

Text File | 1993-07-20 | 7KB | 114 lines

   Eggs and Incubation

    If the nest is neither high and dry nor flooded, loons have a good
chance of hatching their eggs. Within a couple of days from the start
of nesting, the female will lay her first egg. Observing a common loon
lay her egg, McIntyre watched the loon's body rise up and down
nineteen times before the egg appeared. Six minutes of what
appeared to be voluntary expelling activity was required. After
laying the egg, the loon panted and repeatedly opened and closed her
eyes during a twenty-minute recovery period. Probably the degree
of effort relates to the size of the egg. Loon eggs are quite large.
Thirty loon eggs measured by Olson had an average length of 3 3/8"
inches and an average diameter of 2 1/4", about the size of the eggs
of the white pelican, a larger bird. While their color varies
tremendously, even within the same clutch, loon eggs are generally
olive-brown with dark brown or black splotches.

   Typically, there is a one-day delay before a second egg is laid.
Usually loons lay two eggs, but it's difficult to be definitive: a one-egg
nest might well be the leftover from a nest which had an unwanted
visitor, such as a gull, raven or raccoon. Looking at nests in northern
Minnesota, Jim Titus counted seventy-three two-egg nests and fifty-
six one-egg nests, roughly the sixty percent/forty percent split
suggested by several other biologists. While a few three-egg nests
have been documented, they are rare.

   The egg or eggs must be incubated for about a month. While most
bird books list the loon's incubation period at twenty-nine days,
actual incubation time varies greatly. Scott Sutcliffe observed the
incubation of several New Hampshire loons, finding an average
incubation period of twenty-eight days with a range from twenty-
five to thirty-three days. Recording the incubation periods of four
Minnesota loons, Judy McIntyre found an average of twenty-seven
days with a range of twenty-six to thirty-one days. (Knowing just
when incubation begins is often a judgment call by the observermit's
rare for anyone to actually watch a loon lay an egg.)

   While incubating, loons keep their eggs quite warm, around 95íF.
While some birds like the penguin have a featherless brood patch,
loons have a feathered area of their breast where blood vessels in
the skin increase in size during incubation, better transferring the
bird's body heat to the eggs. Like nest building, incubation is shared
by the pair, a behavior common in birds. A loon pair shares nesting
duties about equally. With stopwatch in hand, McIntyre estimated
the average incubation bouts for common loons at just over two
hours for the males and just under two hours for the females, who
typically covered the late evening and early morning shifts. The
length of each incubating session does not seem to follow a rigid
pattern. Owen Gromme, a wildlife artist, recalls a pair of common
loons which changed positions every half-hour; and others have
recorded incubation duty shifts at random intervals.

   One yellow-billed loon demonstrated an extreme devotion to
nesting duty. Sverre Sjolander and Greta Agren watched a yellow-
billed loon incubate a clutch for fourteen consecutive hours. They
never heard this or any other yellow-billed loon call while on the
nest, but common loons often prompt incubation duty changes with
vocalizations. Olson remembers one loon which regularly revealed its
fatigue or frustration by repeatedly broadcasting a long and
mournful wail. After entering the nest, loons usually rearrange
things slightly before settling in. On the nest they sit quietly, almost
always face open water, and watch alertly with the head and neck
extended.

   Incubation doesn't appear to be stressful work. All loons need to do
is turn their eggs occasionally. With awkward-looking but
surprisingly efficient movements, loons turn the eggs at irregular
intervals with partly open mandibles. Yellow-billed loons carry this
irregularity to its extreme. Sverre Sjolander and Greta Agren
recorded egg turnings at intervals ranging from twelve seconds to six
hours. The typical turning interval for common loons is about an
hour.

   When loons are not turning eggs, they are just sitting; as yet, no
one has reported a loon napping on the nest. Loons are faithful
incubators. In 1919, naturalist Arthur Cleveland Bent commented
that incubation "... is practically continuous; the eggs are never
allowed to cool." Judy McIntyre quantified "continuous" at ninety-
nine percent. For each hour of incubation, loons in her studies were
off the nest for only thirty seconds. Even in stressful circumstances,
loons stick to the nest. In her doctoral dissertation on the common
loon, McIntyre described a loon, "whose head could be seen crawling
with blackflies," patiently sitting on the nest for over nine hours
without relief. Trying to keep hordes of blackflies at bay, the loon
shook its head an average of once every ten seconds.

   The need for such stoic devotion to duty has been questioned by
some biologists, citing evidence that loons have successfully hatched
their eggs without a continuous incubation effort. During the 1984
nesting season, the common loons on Massachusetts' Quabbin
Reservoir were carefully monitored. Between July 1 and August 5,
two nesting loons were watched on six occasions with the total
observation time exceeding sixteen hours. A loon stayed on the nest
for the full observation period on only one of the six visits. On July
29, a day of heavy boat traffic, a loon was on the nest just seventeen
minutes during a three hour watch. Over the entire observation time,
the loons were incubating only fifty-five percent of the time, yet the
pair hatched two eggs and successfully raised two chicks.

   Wisconsin photographer Woody Hagge also watched a pair of
common loons break the incubation rules. On an unusually warm day
in May a loon pair, though undisturbed, left the nest for several
hours. Hagge presumes the departure was prompted by the
discomfort of sitting on the nest in the blazing noonday sun. While
loons are able to dissipate some excess heat by panting, sitting in
direct sunlight could possibly overload a bird's cooling systems. Could
it be these loons, with a wisdom acquired over millions of years,
knew the eggs were okay? With the air temperature at 80;ocF, it is
possible that the eggs were being incubated adequately by a
substitute parentmthe sun itself. Of course, the eggs were exposed to
potential predation and the same loon wisdom should have
encouraged the birds to at least stay near the nest. These loon eggs,
by the way, did turn into loon chicks. Many eggs do not.