2017 Eagle Updates
April 06, 2017
Due to unknown circumstances, the second of the two eaglets born this year expired early April 1st. The loss of two eaglets (3/27 & 4/1) is a rare experience at this nest; complete nest failures are not regular occurrences. The 2ndhatchling, born Tues. March 28th, appeared to be sound; moving within the nest bowl and taking food from the parents within one day of hatching. Food was continuously provided over the next three days, and both adults took turns brooding the chick.
Biologists do not know what affected the recently hatched chicks, but possibilities include weather or disease. Weather-related factors such as heavy rainfall during the nesting period can influence the nesting success of birds including raptors. Studies show that inclement weather can drive avian parents to increase their energy outputs and time hunting. Heavy, consistent rainfall may have factored into the male's time away from the nest due to increases in time hunting food and the female’s need to mantle the eaglet to maintain optimal body temperatures. While such weather is not atypical for birds, these components along with any present biological challenges may lead to nest failure (McDonald et al. 2004). On Friday, March 31st, the amount of rain was significant, resulting in 0.8 inches of rain!
Microbes can be components of nests, egg laying, and hatching events. The last blog post (March 16, 2017) began a discussion of possible biological reasons for the death of the first hatchling. Research in trans-shell microbes (Cook et al. 2003) indicates that the probability of infections is high. They have shown that incubation temperatures, timing, green nesting material, and weather conditions play a role in limiting infections across the shell and inside eggs. We may never know if an infection impacted our eggs, but this is another factor in the nesting success equation.
Questions remain about the possibility of a second clutch. According to biologists at NCTC, the possibility of a second clutch is low. If they attempt another clutch, timing, weather, and food matches may pose new challenges for the pair. The amount of energy, stored fat is required to lay new eggs, and impending hot weather are major issues. Bald eagles lay and hatch before the steady summer weather arrives since they can only obtain moisture from the food they consume.
The NCTC Eagle Cam offers us a unique perspective: a ‘sneak peek” into the living room of an apex predator during a crucial time in its life cycle. Although this nesting season may not continue as expected and action in the nest may decline, we plan to keep the Eagle Cam up and running until mid-June or early July keeping an eye out for the adults who occasionally return to the nest.
We thank everyone who watch the live feed, reads the updates and corresponds with our team. We also send a special note of thanks to Terri Bayles, Debi Chiappini, Deb Stecyk, and Doreen Wermer who were integral to our 2016 research initiative to quantify prey deliveries to the nest. They along with so many others are essential to our mission and help us to maintain a watchful eye on the health and progress of this incredible species.
Thanks also to Outdoor Channel, the Friends of the NCTC, Hancock Wildlife Foundation, FWS eagle biologist Craig Koppie, NCTC staff, Lois Johnson-Mead, Clayton McBride, Rob Ball, and all of the long time followers of the cam.
Mar 30, 2017
Hatch day has finally arrived! The pair laid two eggs in late February, however this year, the hatch results were 50% successful. On March 25, 2017, first of two eggs began to show signs of pipping. A viable chick was expected based on the movements observed, and soft sounds heard. Due to circumstances unknown to us, the adults did not begin feeding the new chick. Over the next days (March 25-26), no feeding was observed despite a fish deliveries to the nest. The adults were observed feeding themselves but not the new hatchling.
On March 26th, no further evidence of the first hatchling was seen. Therefore, it is safe to assume based on a lack of feeding and no visual parenting behavior that the first chick did not survive. The parents continued to incubate the remaining egg. On the evening of March 27th, we did observe the 2nd egg moving, and the female was seen gazing down into the nest bowl, indicating that a second hatch was in process. When the pair switched incubation roles that morning, a small pip in the shell was evident! We are fortunate to report that the second hatch was successful and feeding began soon after final hatch March 28, 2017.
The process of pipping occurs when a hatching bird begins to emerge from inside the egg. The egg tooth starts an internal pip with breaking the membrane covering the chick. The shell is porous, allowing for air exchange, and the chick begins breaking inside the egg. Next, the external pip begins. Through internal movement, a special pipping muscle, and breaking the shell chip by chip, the emerging chick creates a larger window in the shell (Brooks & Garrett, 1970). According to raptor biologists at the Raptor Resource Project, it can take a hatchling between 24-48 hours to go from pip to hatch!
We will never know why the first chick did not survive. But a newly emerging chick goes through several significant changes before and during the hatch. Before it hatches, it needs to absorb the egg yolk inside for energy to push and pick at the egg shell. It has to start breathing inside the egg, and immediately after emerging, it has to inflate its lungs sufficiently enough to breathe on its own. With so many variables in the birthing equation, we can see how post-hatch chick survival is a significant feat and a marvel to observe.
March 15, 2017
On Monday, March 13, the eagle pair experienced a significant snowstorm for the first time during this nesting season! The storm continued into the next morning completely immersing the female in snow. She incubated the eggs throughout the night until the male returned to begin incubating the eggs.
One might wonder how an eagle keeps itself and the eggs warm when heavy snow occurs. Bald eagles have unique body features and have also been shown to alter their behavior to modulate heat as temperatures decline (Stalmaster & Gessaman, 1984). Specifically, they retain body heat and minimize heat loss by a) sedentary behavior to slow metabolism, b) slowing blood flow away from the skin to the digestive system, and by having a body covered with over 7,000 feathers. To keep the eggs warm, the brood patch, a featherless area on the chest, is placed against the eggs to keep them at an optimal temperature (99oF), with occasional egg rolls to evenly distribute heat throughout the egg.
While most birds nest during the spring season, this time of the year is optimal for raptors in response to specific environmental cues such as photoperiods and food availability. Apex predators and their offspring need a significant amount of protein for energy and growth, which fish provides. So, egg incubation occurs midwinter, just before fish spawning cycles begin. Once air and water temperatures increase, fish move back to spawning grounds to lay eggs, and these areas are near the foraging regions of the nest.
If you follow the behavior of anglers, one of the first fish caught in the Potomac River each spring are carp. Interestingly, our survey of the 2016 nest revealed the eagle adults also sourced this fish mid to late March, and were immediately fed to the eaglets after hatching!
The success of the nesting pair seems possible despite the weather because this period aligns with the breeding patterns and distribution shifts of their preferred food source, and the animals possess a unique set of physiological characteristics. In essence, the breeding strategy is food related; that is as new food emerges within the habitat, the eagle adults are ensuring that an abundant food supply is available for the rapidly growing eaglets.
March 9, 2017
It’s been two weeks since two eggs were laid at the NCTC nest on Feb. 17th & Feb. 20th. The adults continue to trade incubation sessions throughout the day with the female typically taking the night shift. Once awake, she calls out to the male who returns the call or returns to the nest. As the male focuses on the eggs, turns them, and then settles in to warm the eggs, the female flies away to hunt for food.
During the first week of March, an unusual occurrence happened midday: an intruder came close to the nest. A dark, spotted, large bird was observed descending onto the nest as the male was incubating. The adult immediately flew up to defend the nest and the eggs, scaring off the intruder. This could have been a juvenile eagle as one was seen several times during November as nest building was in initial phases. Raptor researchers report that fledged juveniles rarely return to a nest but it is possible to observe juveniles in the vicinity of a nest, possibly investigating the nest for food.
Nest maintenance continues as the male generally bring large sticks to the nest and occasionally has delivered a small meal to the nest. Mild temperatures and low precipitation occurrences have shaped the early nesting season, but wind speeds up to 50 mph on several days are a concern for a nest that is approximately 12 years old. As the winter season winds to an end, variance in daily weather conditions is to be expected. We can expect spring weather patterns to drive the nesting birds to fine-tune their behavior so they can consistently keep the egg warm, rotated, protected, and alive.
February 22, 2017
Two asynchronous eggs were laid! The first delivery occurred on February 17, 2017, and the second was delivered early morning February 20, 2017. The male and female will now share the task of incubating the eggs, trading between remaining in the nest to protect and keep the eggs warm while the other hunts and forages. We can expect up to three eggs, with the first hatch scheduled to occur on or around March 24th. The second or third hatchings will occur in order of delivery, resulting in a nest of eaglets at different maturity levels.
Several factors are known to drive avian reproduction such as hormonal triggers, temperature, food availability, and most importantly, the photoperiod (changes in day length). In 2016, the female laid its first egg on Feb. 9th when the daylight hours were recorded at 10 hours and 30 minutes, according to the U.S. Naval Observatory. The daylight hours for the February 17, 2017 delivery were almost 11 hours (10 hours and 58 minutes)! Interestingly, the eagle’s 2017 deliveries occurred 2-6 days and 6-8 days later than the 2015 and 2016 dates.
We will continue to observe the adult pair working on the nest, exhibiting bonding behaviors, and assuming the vital role of incubation for the next 35 -38 days.
February 9, 2017
In anticipation of a delivery, the bald eagle pair continues to bring sticks and grass to the nest shoring up the edges and rearranging the nest bowl center. Mating was observed several times in late November, and expectations are that the female will lay within the next week. Predicting the date of an egg delivery can be challenging, and certain factors play a role in shifting dates by one or two weeks.
American bald eagles breed during the winter or early spring when temperatures range from 25 to 45 oF (-4 to 6 oC).Temperature patterns have fluctuated in our region. In January 2017 alone, temperatures readings above 50 oF (10 oC) were recorded for 10 days. Yet bald eagle experts in Alaska believe that food availability and habitat quality drive breeding behavior (mating, nest building, etc.) more than temperature shifts (Hansen, 1987). However, extreme weather and temperatures (heavy snows or rains; below-average temperatures) can make food foraging challenging, leading bald eagles to advance or postpone egg-laying.
Fortunately, the eagles at NCTC harvest excellent food sources from the Potomac River, and this river has a man-made dam just over 1 mile from the nest site. Predicting the exact day of egg delivery may be challenging but the habitat factors within the region are supporting the annual nest success of this raptor pair and keeping those dates fairly consistent from year to year.