incubation

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LMG_4598 Feeding chick on nest

It was actually yesterday when Linda reported that her much-loved and -studied loon pair had hatched two chicks. May chicks are a very good sign! Even a better sign: 75 of 119 territories we observe are on nests, and only 8-10 pairs abandoned their first breeding attempts owing to black fly infestation. In short, we are off to a good start and hope for a bumper crop of chicks in 2015.

Linda’s stunning photo illustrates the exceptional efforts that loon parents make to care for their chicks. In the photo, the female offers a tiny minnow to one hatchling, while the male looks on, and the second hatchling scampers about the nest. In the coming weeks, the pair will offer steadily larger fish to their young. Both pair members — but especially the male — will guard the chicks closely. The male will yodel at any intruders that fly over or land in the territory. He will be particularly vocal this year, because he has two chicks, not just one. The female too will attend the chicks closely when they are young, but she will start to wander off a bit after they reach four weeks of age, leaving her family to forage apart within the territory and even visiting neighboring lakes.

Why do females seem to sherk their parental responsibilities, forcing their mates to take up the slack? We do not know. We suspect, however, that females desert their families and fly off to nearby lakes to draw attention away from their own lake and chicks. You see, intruders are attracted to adults in the water; the more adult loons they see on the water, the more likely intruders are to land. So females with chicks further two goals by “decoying” intruders away from their own lakes. First, they protect their chicks from intruders, which sometimes attack and even kill them. Second decamping females protect their own breeding position on the lake by reducing the likelihood that intruders will find their chicks and target the lake for takeover attempts the following year.

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black fly

Black flies have a terrible beauty. From a distance, they are merely pests, which we must tolerate for a few weeks each year. Up close, they are carefully crafted machines with specialized sensory capabilities and sharp tools sculpted to pierce the skin of mammals and birds and extract the blood they require to nourish their eggs. You have to respect them from the standpoint of evolutionary design.

Yet I spend little time admiring these creatures. Indeed, I dread the two-week period in early May when adult female black flies (Simulium annulus) emerge in vast numbers and descend upon loons. Black flies render each day a trial for loons, which are trying to locate nest sites, mate, build nests and prepare themselves for four weeks of joint incubation. Hounded by flies throughout daylight hours when they are above water, loons drop their normal routine and begin to dive incessantly to minimize blood lost to the flies. Breeding pairs that have completed nests and laid eggs are often forced to abandon efforts to incubate them owing to the relentless insects.

In the past several days, fly populations have spiked, and loon pairs are now suspending their breeding efforts for the moment and simply ditching the flies. We hope that loons’ nesting efforts are not so closely synchronized with fly emergence this year as they were last, when black flies reduced loon breeding success dramatically. If this is a typical year, a small percentage of loon pairs (say, 10-20%) will abandon their eggs on account of the flies, but many more pairs will persevere in spite of the pests. So our hopes for a banner year of chick production are, as yet, intact.

Although their travails pale in comparison to what loons face, even loon researchers are impacted by black flies. Eric, Joel, and Chris are in the final stages of covering the study lakes for the first time. Since they are trying to observe leg bands of loons that are diving constantly to avoid flies, the LP team will confront a steep challenge in the next few weeks. I hope they are up to it!

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After the black fly debacle in recent weeks, we were all ready for some good news. Indeed, most territorial pairs had shaken off the flies and gotten back to the business of reproduction. Good tidings seemed the order of the day. Yesterday, Al Schwoegler of West Horsehead Lake called with a thrilling and unexpected report: the eggs laid by the pair, which they had left unattended for many long hours on several days because of the torment of black flies, had begun to hatch! At first neither Al nor I could believe that the eggs were viable. As Al described the behavior of the female on the nest — who has reared a whopping 19 chicks to fledging since 1996, when she was first banded — we gradually let ourselves believe that the impossible had occurred.

But our positive feelings were dashed suddenly by the cruel realities of loon territorial behavior. You see, the last few weeks at West Horsehead have been marked by frequent territorial intrusion. At the very time that the pair was trying to recover from the onslaught of biting insects, the male owner was facing repeated challenges for his position. Finally, by yesterday, both Al and Sally Yannuzzi of my team confirmed that male ownership had passed from the 14 year-old male hatched on Alva Lake who had resided on the lake for most of the past decade to a 9 year-old upstart from Harrison Lake in Lincoln County. The new male, confident in his new position, spent much of the morning resting and foraging near the nest, while the female patiently sat on the eggs. Finally, the female slid off of the nest into the water, revealing a newly hatched chick and second egg, which was on the brink of hatching. Alas, the new male behaved as animals typically do when confronted with helpless young that are not their genetic offspring: he quickly pecked the chick to death as its mother looked on helplessly. The celebration of an unexpected hatch gave way to a wake for a young loon doomed by territorial usurpation. Al took this photo of the female, still mildly protective of her nest containing the dead and unhatched chicks. (Shortly after the photo was taken, the female left the nest to forage with her new mate, with whom she might still renest.) IMG_20140616_134217_724Sorry for the unpleasant photo and description. But there is a valuable lesson here. Loons, like lions and langurs and mice and water bugs, behave so as to promote their own reproduction. Despite the ugliness of this episode, we can hardly hold it against the 9 year-old that he is looking to produce his own biological offspring — before a new usurper comes along and shows him the exit.

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To be sure, 2014 is shaping up to be a dismal breeding season. Ice-out occurred weeks later than usual, owing to thick ice and cool weather in March and April, and delayed breeding for all loon pairs. The ensuing warmup in May caused the black fly population to explode to higher levels that we had ever seen. Pairs that had just laid eggs were blanketed by the relentless bloodsuckers and incubating males and females driven off their nests at rates never seen before. In short, almost all loons abandoned their first nests.

Although it is counterintuitive, loons are probably more vulnerable to nest abandonment than many other birds because males and females incubate the eggs equally. Consider the plight of loons trying to incubate their eggs to hatching for 27 days in the presence of black flies. Each pair member must incubate for stretches of several hours before being relieved by its mate. The rotation system must be efficient enough that eggs are incubated over 99% of the time. When not sitting on eggs, a breeder rests, preens and forages to replenish its energy reserves. If either pair member fails to incubate, the nest is doomed to failure, because its mate cannot compensate for missing incubation by remaining on the eggs at all times without long breaks for foraging. So we have a case where the weakest link breaks the chain. Even a tough, determined male incubator is destined to lose a clutch if his mate is less determined than he is and refuses to sit on the eggs and tolerate the torment of biting insects.

We have learned about the necessity of dual incubation from past observations. Nest abandonment commonly occurs following territorial eviction of a pair member during incubation. If its mate is evicted by an intruder, the remaining pair member usually continues to sit on the eggs for a time. With rare exceptions, though, its new mate (the usurper) does not incubate — why should it sit on eggs containing young to which it is unrelated? — the cycle of shared incubation duties breaks down, and the nest fails within a day. (If it is early enough in the season, such pairs will lay a new set of eggs that both will incubate.) A rarer cause of nest failure during incubation is death of a pair member. In 2005, the female on Alva Lake was killed by an eagle while sitting on the eggs. The male valiantly sat on the eggs, taking breaks to forage from time to time, even as female floaters competed in front of him to fill the breeding vacancy. Despite being within a week of hatching, this male could not complete incubation on his own, and the nest was lost.

Enough talk of failure! I will end on an up note by showing you the sweet photo that Linda Grenzer took of a breeding male sitting on a nest. This bird and his mate both tolerated the record outbreak of blackflies earlier in the season and were rewarded with a little fuzz-ball — a much-needed reminder that all is not lost this year. Let’s cross our fingers that other pairs, many of which are incubating a new clutch of eggs after abandoning the first, will be able to duplicate this effort.

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On Manson Lake, the long-time male breeder was displaced in May of this year by a younger male. After seizing control of the territory, the usurper proceeded to nest with the long-time resident female.

But the original territory owner did not give up on his territory easily. He remained in the vicinity and was a frequent intruder into his old domain. In fact, between the 13th and 19th of June, the old male drove off the usurper and regained ownership of his territory. At this point, incubation by the female and the usurper was well underway, and the eggs were within 10 days of hatching. The female continued to incubate the eggs, and the old male — though he had played no part in the reproductive effort and had not fertilized the eggs — defended the nest. (We did not observe him to incubate the eggs, however.) When the eggs hatched, he treated the chicks as his own.

Territorial usurpation creates some awkward reproductive decisions for loons. It is common for a breeder to lose ownership of the territory during a breeding attempt. In most cases, incubation ceases, and eggs are abandoned. If there are chicks present, they are often killed by the usurper, while the remaining pair member looks on helplessly. Manson is not the only lake where a usurper has seized control of a territory but continued to care for offspring that do not belong to him. In fact, we have observed at least 5 other cases of such behavior — all among males. That is, we now have 6 cases where a usurping male has wrested territorial ownership away from the male breeder but either permitted the young to survive and be reared by the female breeder (2 cases) or seamlessly stepped in to assume paternal responsibilities (4 cases). I am beginning to see a pattern!

Evolutionarily speaking, animals should behave so as to maximize the number of their own young they contribute to the next generation. It is generally unexpected to see animals care for young that are not their biological offspring.  I will continue to be on the lookout for more examples of such behavior in loons — and will puzzle over the apparent tendency of male usurpers, but not females, to be willing to adopt the offspring of their predecessors.

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It is still early, but I can already see that 2013 will be a good year for chick production in northern Wisconsin. Thirty-nine of about 120 pairs that we follow have hatched chicks already, and 24 other pairs still have active nests and might produce chicks. Since it is always a dicey proposition to incubate eggs for four weeks without a raccoon eating them or some other calamity befalling them, having almost half of all pairs rear chicks successfully is cause for celebration. We are feeling good about the population.

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In the past five days, the list of lakes with a chick or chicks has grown to five. The list is growing, but still small. We cover over 100 lakes in Oneida, Lincoln and Vilas Counties, so this constitutes less than 5% of our study lakes. It is still early! Don’t panic if your breeding pair has not even nested yet or has failed in a first attempt. There is still time for them to bring off a brood.

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We are happy to report the first hatch of the season. This one occurred on Jersey City Flowage, our southwestern-most lake, and was found by Jacki, my student from Chapman. JCF had the earliest hatch in the study area last year, as well, so they are staying true to form. We are hoping for many more chicks soon, but don’t hold your breath; this pair seems to be at least a week ahead of other early nesters.

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Great news! Our manuscript that describes natal site matching was just accepted for publication in a prestigious ecological journal. Very exciting to get the story out there that young loons have a strong statistical tendency to settle on breeding lakes that match their natal lake in both size and pH.

From the field….about half of our breeding pairs are now incubating eggs. Although blackflies are moderately bad, they do not seem to be terrorizing the loons enough to cause them to abandon their nests. I am anticipating a good year for reproduction in Oneida County. (Fingers crossed, as always.)