Day One

On the 16th I was able to spend some time with both pairs of Parasitic Jaegers. I located both nests in the same day, and based on their behavior previous visits, I can estimate within a week when the eggs should be hatching. I will from now on refer to them by their AOU code, PAJA. It makes writing a bit easier. 

I first spent some time with the second pair, which I previously said I probably would not get as much time to observe. However, I think discovering that one pair has a full clutch of two eggs (Pair 2) and the other only has one egg (Pair 1), that I will try (time permitting) to observe both equally. For this first observation though, I only spent enough time to find Pair 2's nest and observe them briefly. 

Behaviors are defined as below.

Defending – defending nest/brood from potential predators, including observers. It also defines the “broken-wing” display defense

Incubating – sitting on nest, incubating egg

Hunting/Foraging – actively flying in search for prey/food item, defined by bird in flight and scanning ground or hovering in one place above prey/food item. If one bird leaves area and is out of sight of observer, it is assumed they are hunting/foraging until they are seen again

Preening – preening feathers, bathing in water

Loafing – standing/sitting on tundra with no apparent purpose

In flight – in air flying with no apparent purpose

Brood – attending brood/young

Altercation – with other bird that is not explicitly due to defending of nest/brood

PAJA Pair 2            Date: 6/16/14            Time of observation: 9:50 - 10:25

Temperature: 34 F    Wind at 11-27 knots   Light fog

Type of Behavior	Total Time Dark Morph	Percent time spent doing behavior	Total Time Light Morph	Percent time spent doing behavior
Defending	15	42.86	9	25.71
Incubating	2	5.71	24	68.57
Hunting/Foraging	0	0	0	0
Preening	0	0	0	0
Loafing	15	42.86	2	5.71
In flight	0	0	0	0
Altercation	3	8.57	0	0

Total time spent observing: 35 minutes

I made this kind of chart for both pairs, although since my time was so brief with Pair 2, it really could not be used for much scientific analysis. This pair defended against me obviously. I think also because it was quite cold, that they went back to incubating when I was still within 40m of the nest. They also defended against a Common Raven and Glaucous Gull. The dark-morph of this pair chased away a pair of Canada Geese and Greater White-fronted Geese, apparently for no reason at all.

PAJA Pair 2 nest with two eggs

Dark morph of PAJA Pair 2

 

PAJA Pair 1              Date: 6/16/14                 Time of observation: 13:35 - 15:01

Temperature: 34  F    Wind at 11-27 knots    Sun shining

Type of Behavior	Total Time Dark Morph	Percent time spent doing behavior	Total Time Intermediate Morph	Percent time spent doing behavior
Defending	15	17.44	16	18.6
Incubating	50	58.14	20	23.26
Hunting/Foraging	4	4.65	8	9.3
Preening	8	9.3	18	20.93
Loafing	8	9.3	21	24.42
In flight	1	1.16	1	1.16
Altercation	0	0	2	2.33

Total time spent observing: 86 minutes

This pair has gotten even feistier; I didn't even try to get pictures of their nest because of their incessant dive-bombing. They only have one egg, and may be more defensive as a consequence. They defended against another PAJA, as well as a Pomarine Jaeger. I may not have mentioned this before, but the previous two years I was here, I only saw Pomarine Jaegers in the beginning of the summer. They are a species that is highly dependent on lemming populations as a food source. Although we have not seen many lemmings, they are sticking around, and we have even found a nest near some of our study plots. 

I also observed a Long-tailed Jaeger, a Glaucous Gull and a Short-eared Owl fly by the pair, but they did not defend against any. Again, begging the question, if they are capable of recognizing individuals of different species so that they do not invest time and energy in defending when the bird flying by is not a threat.  

I am hesitant to say that the dark morph in both pairs is the female based on what I have read about polymorphism being attributed to sexual selection in these jaegers. However, they also exhibit reversed sexual dimorphism, where the female is larger than the male, and I am positive that PAJA Pair 1's dark- morph is larger than the intermediate-morph. Plus, I would assume that the female incubates for a longer period of time, and the dark-morph was incubating for 50 minutes, 58% of the time that they were observed. Also, in previous year's the dark-morph has been the primary parent attending the brood. So, I guess I will see if there is more information on this, and try to have a better idea of which individual is which.